Contaminantvariabilityin asedimentationarea oftheriverrhine

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1 Cntaminantvariabilityin asedimentatinarea ftheriverrhine

2 Prmtren: Dr.S.B. Krnenberg, Hgleraar Gelgie Landbuwuniversiteit Wageningen Dr. L. Lijklema, Hgleraar Waterkwaliteitsbeheer Landbuwuniversiteit Wageningen

3 ,---> Herman Winkels Cntaminantvariability in asedimentatinarea ftheriverrhine Variabiliteitvanverntreinigingen ineen sedimentatiegebied vande Rijn PROEFSCHRIFT terverkrijging vandegraad van dctr pgezag vanderectr magnificus vande Landbuwuniversiteit Wageningen, Dr.C.M. Karssen, inhet penbaar te verdedigen p maandag 8 december 1997 des namiddags te vier uurin deaula. au\a2.'i<9

4 CIP-DATAKONINKLIJKE BIBLIOTHEEK, DEN HAAG Winkels, HJ. Cntaminant variability in asedimentatin areaf the river Rhine/ Hermannus Jhannes Winkels. - [S.l.:s.n.] Thesis Wageningen. -Withref. -With summary in Dutch. Van Zee tt Land nr.64 ISBN Subject headings: sediment variability / cntaminatin The research described in this thesis was carried ut at Rijkswaterstaat, Directrate IJsselmeergebied and at the Institute fr Inland Water Management and WasteWater Treatment (RIZA), Lelystad, The Netherlands ' BIBLIOTHEEK LANDBOUWUNIVERSITEIT WAGENINGEN

5 Stellingen /J ÎJ n 3 cp 1. Bij het kiezen vr een bemnsteringsstrategie van waterbdems dient alle ruimtelijke infrmatie ver het ntstaan en de verntreiniging van de sedimenten te wrden gebruikt. (dit prefschrift) 2. Een bemnsteringsprgramma vr waterbdems wrdt vaak gebaseerd p een equi-distant rster f er wrdt gebruik gemaakt van geneste bemnstering. Waterbdems meten echter bemnsterd wrden in een fijnmazig grid in cmbinatie met enkele ruimtelijk verspreide waarnemingen. (Warrick and Myers, 1987; Webster and Oliver, 1992) De diepte tt welke verntreinigd slib dient te wrden verwijderd in het Ketelmeer verschilt per te saneren deelgebied. De nauwkeurigheid waarmee de sanering per deel-gebied uitgeverd kan wrden is afhankelijk van de extra diepte die als veiligheidsmarge vr de sanering van elk deelgebied wrdt aangehuden. Daar waar de verntreinigde laag dikker is, zals te Ketelhaven, zullen de ksten per m 2 hger zijn m dezelfde nauwkeurigheid te halen als elders in het Ketelmeer. (dit prefschrift) De stuwmeren in het strmgebied van devlga vrmen een chemische tijdbm. (dit prefschrift) 5. Oude ldingskaarten geven niet meer dan een indicatie van de waterdiepten en zijn nderling niet vergelijkbaar, daar ze met nnauwkeurige en verschillende methden zijn bepaald. (dit prefschrift) 6. De Nrdzee en dewaddenzee zijn in hge mate afgeschermd van verntreiniging dr het afdammen van de riviermndingen van de Rijn dr de aanleg van grte waterstaatskundige werken. Naties die de verantwrdelijkheid p zichhebben genmen vr deze zeeën, meten daarm meebetalen aan de sanering van de hierdr verntreinigde waterbdems in Nederland.

6 7. Hydrlgische mdellen meten altijd getetst wrden aan de uitkmst van veldnderzek. 8. Gedheid is veel belangrijker dan verstand. (Edith Stein) 9. Het is ngerijmd dat verkeersdrempels, rtndes en stplichten wrden aangelegd p nageneg elke kruising in Nederland m de verkeersveiligheid te vergrten, terwijl tegelijk verkeerslessen uit het basisnderwijs verdwijnen. 10. Natuurntwikkeling in Nederland is vergelijkbaar met het werk van een filatelist; de verzameling begint pas ergens p te lijken als deze nageneg cmpleet is. 11. Succes hebben wil niet altijd zeggen dat het ged gaat. 12. Blijf daar wnen waar uw geluk is, want geluk is uiterst gevelig vr verhuizing. (Carpl Wageningen-Lelystad) Stellingen behrend bij het prefschrift van H.J. Winkels: Cntaminant variability in a sedimentatin area f the river Rhine Wageningen, 8 december 1997.

7 ne small step fr science sake, I did it.. Fr Mara

8 mslag: Fiel v.d. Veen figuren: Fiel v.d. Veen/RWS DTP en drukwerk: Evers Lith & Druk cördinatie prductie: Henk Bs

9 CONTENTS Page Summary 9 Chapter 1 General intrductin 13 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Chapter 8 Gechrnlgy f pririty pllutants inlake Ketelmeer, a sedimentatin area f the river Rhine 25 Distributin and gechrnlgy f pririty pllutants in alarge sedimentatin area, river Rhine,the Netherlands 43 Gechrnlgy f pririty pllutants in sedimentatin znes f the Vlgaand Danube delta incmparisn with therhine delta 55 Optimal cst-effective sampling fr mnitring and dredging f cntaminated sediments 73 In-situcnslidatin f lake depsits:an empirical mdel t recnstruct pllutin histry 95 Dilutin f riverineheavy metalinput byresuspensin and algal grwthin Lake IJsselmeer, thenetherlands 107 Mdelling diagenesis f aquatic sediments and dispersin f cntaminants in LakeIJsselmeer (thenetherlands) 125 References 145 Samenvatting 151 Dankwrd 157 Listfpublicatins 159 Curriculum Vitae 161

10 Summary Aquatic sediments in sedimentatin znesfmajr riversarein general sinksfr pllutants.thesedimentatin zne Ketelmeer/IJsselmeer isan imprtant sinkfrcntaminantsf the river Rhine (i.e. river IJssel).Recent and histrical pllutin interact here.redistributin f suspended slids and ersinf depsited sediment in theshallw Dutch lakes (duetwaveactin) arelikely t change cntaminatin levels f sediments in these lakes, which is the subject f this thesis. The aim f this research was t study and explain the variability f cntaminants in the sedimentatin area Ketelmeer/IJsselmeer in rder tpredict thefate f thecntaminants in thefuture. Fr thispurpse anumberf methdlgies and mdels weredevelped and/r adapted. Chapter 2 describes the cllectin and analysis f sediment cres, tp-layer sediments and gelgically different layers in Lake Ketelmeer. Sediment cres were sectined int thin slices and the yearf depsitin f each layerwasdetermined usingradi-chemical analyses. Thecntaminant cncentratins were pltted versus the year f depsitin f each sediment layer t (re-)cnstruct the histry f cntaminatin. Similar vertical changes in cntaminant cncentratins were fund as in a numberf sedimentcressampledinsandpitsin LakeKetelmeer.Further,differences in cncentratin between the tp-layer sediments and the degree f cntaminatin in the entire recent IJsselmeer depsits (IJm-depsits) f Lake Ketelmeer were fund. The lder Zuiderzee depsits (Zu-depsits) underlying the IJm-depsitshavelwbackgrund valuesfr heavy metals,pahsand PCBs. This indicates that dwnward transprt f these cntaminants with infiltrating water is negligible in this lake. The cncentratins f metals and PAHs in the sediment cres reflect, withut any serius alteratins, the histricalinputf the pastfive decades. Thepllutin histryis characterizedby,in the early 1940s, lw cncentratins f metals and already elevated levels f PAHs; a pssible reductin f these cntaminants during the Secnd Wrld War and attaining, their highest levels between 1955 and Rather lw levels ccur in recently depsited sediments, sme f which are the lwest ever bserved verthelast five decades (Pb,As,and all studied PAHs). Almst allchlrinated cmpunds shwed a certain decline in cncentratin in anaerbic sediments as cmpared t samples f the tp-layer cllected in 1972 and stred in the labratry, which still reflect the riginal pllutin input. Fr several PCBs thisdeclineprved tbesignificant; itmay have been caused by micrbial dechlrinatin reactins in the anaerbic sediment.cnsequently, the cncentratinprfiles fthe chlrinated cmpunds dnt reflect the riginal pllutin histry directly.despite the attenuatin f cncentratin, peaksin PCB cncentratinprfiles werestillbserved.thefllwing trendsincncentratins fpcbs can be currently bserved inlake Ketelmeer sediment: - Almst allpcbs studied hadrather lw cncentratins intheearly 1940s. - The highest levels f PCBs ccurred between 1960and Recently depsited sediments alshaveelevatedlevelsf PCBs ascmpared t thelevelsin layers frm theearly 1940s. Overall, recently depsited material is far less-plluted than sediment depsited in the 1960s and 1970s. These findings prve that in this lake lder, highly plluted sediments are buried under a yunger,less-plluted layer.hwever,atsmelcatins,suchasindredgedpartsrersiveznes, the

11 SUMMARY highlyplluted layersmayremain uncvered, saquaticrganismsmay still beexpsed t highlyplluted sediments frm the 1960sand 1970s thrugh thebenthic fd chain. In Chapter 3 attentin isfcused n the distributin and gechrnlgy f the sediments f Lakes Ketelmeer and IJsselmeer. The cncentratins f metals, PCBs, PAHs and varius sediment characteristicsweredetermined in 77samplesfthesurface sediments andne 3 m crefbthlakes. Abslute cncentratins f these pllutants were nrmalized fr sediment cmpsitin (e.g. clay fractin andrganicmattercntents).inlakeijsselmeer theyungest gelgical layer (Um-depsit)ismainly fund in deep sedimentatin areas (25%). This depsit is severely plluted in Lake Ketelmeer (Chapter 2).Cncentratins f all plluting cmpunds in the IJm-depsit f Lake Ketelmeer prved t be times higher than in Lake IJsselmeer. Cncentratins in the same depsit in Lake IJsselmeer were 2-4 times higher than thse in the lder sandy sediments f the lake. Cncentratins f heavy metals, As and PCBs initially increase with depth, but then decrease t lwer r even backgrund levels.thiscrrespnds with theinputsf the riverijsselduring thepast five decades.as the distance frm the river muth (i.e. Lake Ketelmeer) t Lake IJsselmeer increases, there is a decrease in the degree f pllutin in this IJm-depsit. The hypthesis is develped that primary prductin (with related calcite frmatin) and mixing with erded sediment frm elswhere in Lake IJsselmeer are tgether respnsible fr this dilutin. Chapter 4 describes the cre sampling and analysis fr tw similar sedimentatin znes f tw majr river deltas. Unifrmly sft anxic sediments in the Vlga and Danube deltas were cllected, using satelliteimages,whichreflect thecncentratin f suspended slids.cesium-istpe datingand measurement f the cncentratin prfiles f heavy metals and PAHs,which reflect (withut serius alteratins) thehistric pllutin input int theserivers,wereused inthe cmparisn. The cntentsf the 7 PCBs investigated and f cadmium were belw the detectin limits fr all sediment samples in thevlgaanddanubedeltas.lw,mrer lesscnstantcncentratins f arsenic, cpper,zincandall studied PAHswere bserved in sedimentsf the last five decades inthevlgariver.nickel cncentratins in Vlga delta sediments were rather high, and recently depsited sediments seemed t shw slightly increasing levels fr zinc, chrmium and arsenic. The pllutin histry f the Danube is characterized by lw cncentratins f metals but elevated PAH levels in the early 1940s; increasing levels f metals and PAHs between 1950 and 1987;and decreasing levels in mre recently depsited sediments. When cmparing the cncentratins f heavy metals, PAHs and PCBs in the aquatic sediments f the rivers Rhine, Danube and Vlga deltas fr the past fivedecades it is evident that the Vlga delta was, and still is,the cleanest f the three. A cmbinatin f natural (backgrund) inputs, industrial inputs and man made technical changes in the river systems (like the building f strage lakes)canexplain mstdifferences inthe histricalcntaminantprfiles fthe three deltas.nwadays the cncentratins f heavy metals (except cpper and nickel), PAHs and PCBs in sediments f the river Rhine are still higher than in the ther twrivers,butthe sediment lading rate fr heavy metals (except cadmium and zinc)f thedanube ishigher thanfr the ther tw rivers. In Chapter 5 the gestatistical sampling apprach chsen fr Lake Ketelmeer is explained. When mnitring cntaminants and related sediment characteristics in an aquatic envirnment, their spatial variability needst betaken int accunt.the sampling strategy cvered shrt-distance variability (65 m) and lng-distance variability (500 m) f the investigated variables. In Lake Ketelmeer we chse three sub-areas. The distances between sampling pints takes int accunt the size f each sub-area. With this apprach the number f sampling pints needed t mnitr trends f cntaminants in sediments can beminimized, taking int accunt the necessary accuracy. Thechice f sampling strategy fr mnitring sub-areas, characterised by either water depth, sedimentatin/ersin behaviur r sediment type,willresult indifferent sampling spacings.fr example,inlake Ketelmeer the ptimal samplingdistancefr mnitringbenz( A)pyrene (BAP)in the centralpartf the lake was largerthan 10

12 SUMMARY near the harbur and shre,where gradients in water depth are steeper. Thus,when designing a dredgingprgramme tremve seriusly cntaminated sediments, theidentificatin f sub-areas is essential tensurethe adequate dredging f the sediments.if spatialvariability isnttaken int accunt fr dredging cntaminated layers, seriusly cntaminated spts may be verlked r rather clean sediments may be dredged needless. Thrugh (althugh expensive) spatial investigatins f the cntaminated layer befre dredging starts, identifying critical sub-areas, is therefre recmmended. Practical,cst-effective, gestatistical methds allw anefficient usef limited financial resurces fr mnitring aquatic sediments. Anther imprtant prcess affecting sediment cncentratin prfiles is cnslidatin. Chapter 6 deals with this physical prcess f settling f suspended slids and the lss f water after depsitin. Cnslidatin in principle can be described by mathematical mdels, but because f lcal circumstances in the Lake IJsselmeer area an empirical apprach seemed mre reliable. Five representative cresf theurn-depsit weretakenfrm deepznesfthe lakes. Peridicwaterdepth surveysat these lcatins ver the last sixty years prvided infrmatin n the net sedimentatin rate and ttal thicknessf theijm-depsit atknwn time intervals.t calculate a time-equivalent f thedepth scale,crrectin factrs fr sediment cnslidatin were needed. These factrs were based n a simplificatin f thevarius stagesf cmpressin (i.e. 0%, 30%and 45%). Afactr n, whichrepresents changesf water cntent f the sediment as adependent variable f clay cntent, wasderived fr each layer, makingit pssiblet determinetheinitial, uncmpressed thicknessfeachlayer byaninversecalculatin prcedure. Hence, a fairly reliable time-scale fr depth culd be recnstructed. This time-scale was cmpared with radi-istpe-dated layers andtheresults shwed clse cnsistency. Annual variability f cntaminants in theijsselmeer area isdescribed in Chapter 7. Measurements f the cncentratins f six heavy metals in suspended slids, discharged by the river IJssel, and settling slids attw lcatins in LakeIJsselmeer shwed a typical spatial gradient. Theheavy metals cncentratins decreased withincreasing distancefrm theriver IJssel inlet. This spatial gradient crrespndswithgradientsbservedin the bttmsediment (Chapter 3). Measurementsinsediment cres frm Lake Ketelmeer, i.e. the river muth, and the central part f Lake IJsselmeer shwed that the heavy metals cncentratin in sediments, depsited during the same perids, is 2 t 3 times higher in Lake Ketelmeer than in Lake IJsselmeer. The cncentratin gradient in the settling slids is still significant when changes in the clay and rganic matter cntent are accunted fr by using nrmalized metal cncentratins. Arugh sediment mass balance fr heavy metals,based n riverinput data and bserved sedimentatin fluxes, indicates thatthettalinternal sedimentatin fluxes fheavy metalsin Lake IJsselmeer far exceed the external aereal lading by the river. Due t thecmplexity f therelatinships between the measured variables, theheavy metal cncentratins and variablesrelated t primary prductin and ersin, single crrelatin analysis did nt reveal clear relatins and prcesses that culd explain this dilutin. Principal cmpnent analysis and stepwise multiple regressin hwever shwed that the variatin in the heavy metals cncentratin in settling slids is related t wind velcity and clay cntent, bth f which are related tresuspensin/ersin f sediments; r alternatively, t ph, chlrphyll and CaC0 3, which arein turn related t algal grwth in the lake. Resuspensin/ersin-related variables are the dminant factrs explaining the variatin in heavy metals cncentratin in the suthern part f Lake IJsselmeer, whereas algal-grwth-related variables explain mstf thevariatin inthemetal cncentratins in settling slidsinthe central part f the lake.inthis central part, where algal cncentratins are high, the negative relatin between the cncentratin f mst f theheavy metals in settling slids andthechlrphyll and rganic matter cncentratin in the watercmpartment justifies the cnclusin thatdilutin fcntaminated suspended slids by primary prductin is activethere.inthe suthern partf the lake, theheavy metals cncentratin is psitively related t wind velcity and clay cntent. This indicates that resuspensin f recent depsits cn- 11

13 General intrductin Intrductin In the aquatic envirnment chemical substances, including heavy metals, arsenic, plychlrinated biphenyls (PCBs) and plychlrinated armatic hydrcarbns (PAHs), riginating frm natural and cultural (industrial) pint surces andfrm diffuse surces, have beendetected during thelast decades (Annymus, 1992; Beurskens, 1995). These cntaminants tend t cncentrate n slids, either suspended r settling and in sediments. The fate f these cntaminants in lakes r rivers depends n physical transprt, physic-chemical distributin, and transfrmatin prcesses (Kelmans, 1994). Characteristicsf the aquaticsystemas wellas the prpertiesf the cntaminantinquestin determine therate and extent f prcesses liketransprt by waterflw, sedimentatin, resuspensin, ersin and (pht)-(bi-)chemical degradatin (Baughman and Burns, 1980; Burns and Baughman, 1987). In sedimentatin znes,where streamvelcities decrease, thesuspended slids settlewiththe assciated cntaminants.themain sedimentatin znesfmajr riversaretheir deltas.here accumulatin f cntaminated suspended slids is likely t ccur. The flw f water and the depsitin f particles in deltas is different fr each river.it depends e.g. n the rigin and discharge f the river, the sizef the catchment area, the slpe f the riverbed between catchment area and delta, stream velcities in branches, marine prcesses such as surf and tide (tidal interactins) andtheanthrpgenic influences, like canalizatin and riverbed cntrl (Summerfield, 1991; Reading, 1996).The anthrpgenic influences respnsible fr cntaminatin in the entire catchment area will therefre result in spatial and tempral cntaminant variability inthe deltas. The river Rhine enters the Nrth Sea in the Netherlands; it drains a highly industrialized part f nrthwestern Eurpe. The river has a cntrlled (endiked)riverbed, is partlycanalized and hasitsmain sedimentatin znes in frnt f the Dutch castline, due t castal prtectin wrks. Sedimentatin ccurs further in majr lakes in central (Lake Ketelmeer/Lake IJsselmeer) and western parts (Hllandsdiep/Haringvliet)f thenetherlands.during thelastdecades water quality mnitring prgrams have prvided infrmatin n the pllutin histry f this river. Als sampling f sediments in the sedimentatin znesf this river started during the last decade, as a preparatin fr future dredgingf cntaminated sediments intheselakes. Aquatic sediments in sedimentatin znes f majr rivers are in general sinks f pllutants (Salmns and Förstner, 1984; Van der Weijden and Middelburg, 1989). The sedimentatin zne Ketelmeer/IJsselmeer isanimprtant sinkf cntaminants f theriverrhine (i.e. river IJssel).Recent and histrical pllutin interact here. Redistributin f suspended slids and ersin f depsited sediment in the shallw Dutch lakes (due t wave actin) is likely t change cntaminatin levels f sediments inthese lakes,which isthe subject f this thesis. Theaimfthisresearch iststudy andexplain thevariability fcntaminants inthe sedimentatin area Ketelmeer/IJsselmeer in rder t predict the fate f the cntaminants in the future. Therefre methdlgies and mdels are develped and/r adapted in this study. Belw general infrmatin is presented n the studied IJsselmeer area and its cntaminant levels in the central part f the Netherlands.The utline f this thesis ispresented inthe last sectin. 15

14 CHAPTER 1 Fig TheIJsselmeer area. 16

15 INTRODUCTION Usselmeer area Befre 1932the Zuiderzee in the centre f the Netherlands had an pen cnnectin with the Wadden Sea (Fig. 1.1), which is cnnected t the Nrth Sea. Hence the water was saline. In this envirnment during theperid ,the Zuiderzee sediments (Zu-depsits; Fig. 1.2), were depsited in this area. These sand r clay depsits can be visually identified by the presence f shell fragments (Mya arenaria). The Zuiderzee Prject invlved the damming f the Zuiderzee, the creatin f a large freshwater lake, named the Usselmeer, and the creatin f ver 2000 km 2 f new land (Van Duin and De Kaste, 1985; Van Duin, 1992).With the reclamatin f the plders f Flevland als brder lakes were develped between theseplders and themain land ntheeast and Suth sides (Fig. 1.1;numbers 1-8). When theinfluence f tidal waves with their strng ersive ptential was excluded frm this area, the riginal waterdepthsreadjusted t thenew cnditins.in theseshallwfreshwater lakestheimprtance f water mvement, hrizntal transprt f slids by advectin and dispersin, resuspensin f bttm sediment due twind-induced wave actin, sedimentatin and ersin became dminant (Van Duin, 1992). Ente (1981) shwedthatdeeper znesinlake Usselmeerand Markermeer became mre shallw due t depsitinffreshwater sediment. Hedefined thesefreshwater mstly lamy sediments depsited during theperid 1932 till nwadays astheijsselmeer-depsit (Um-depsits).Um-depsits arethught t be partly erded Zu-depsits mixed with settling sediment entering the areathrugh the river IJssel. Table 1.1. Cmparisn f sizes,water depths and range f cntaminatin in the tp layer sediments f all interlinked lakesin theusselmeer area. Lake Ketelmeer (n = 36) Lake Usselmeer (n-= 54) Lake Markermeer (n = 35) BrderLakesFlevland' (n = 86) Size (km 2 ) Aver,waterdepth (m) L Rangef cntamin. (mg/kg) Aver, (stand,dev.) As 20- Cd 4- Cr 67- Cu 84- Hg 1.1- Pb 91- Ni 44- Zn 918- E7PCBs SlOPAHs (3) 27 10(6) (62) (26) (0.5) (43) (4) (342) (0.16) 12.1 (2.9) (7) 2(2) 38 (29) 22 (18) 0.4 (0.4) 36 (33) 17 (13) 30 (233) 0.03 (0.03) 2.0 (1.7) (5) 0.7 (0.3) 55 (15) 18(7) 0.2 (0.1) 28 (16) 20(5) 126 (78) 0.03 (0.01) 1.7 (0.8) (5) 0.9 (0.7) 27 (21) 14 (14) 0.1 (0.2) 19 (24) 17(11) 136 (138) 0.05 (0.06) 4.6 (10.8) Brder Lakes Flevland: Lake Gimeer, Lake Eemmeer, LakeNijkerkernauw, Lake Nuldemauw, Lake Wlderwijd, Lake Veluwemeer, Lake Drntermeerand LakeVssemeer (numbers 1-8 in Fig. 1.1) PCB-cngeners (IUPAC n.): 28, 52, 101,118, 138, 153and 180 PAHs: fluranthene, benz[k]fluranthene, benz[a]pyrene, flurene, benz[b]fluranthene, anthracene, phenanthrene, benz[ghi]perylene, indenpyrene and chrysene 17

16 CHAPTER 1 Fig The sediments f the Zuiderzeebefre the enclsure f the barrier dam in 1932.

17 INTRODUCTION During theperid all interlinked lakesinthis areawereinvestigated fr their gelgical structure, tplayer cmpsitin and the degree f cntaminatin f this tplayer at 211 lcatins. Present sediment types fr all interlinked lakes are given in Figure 1.3. Present lake sizes, average water depths and range f cntaminatin fr heavy metals and the grups f 7 plychlrinated biphenyls (PCBs)and 10 plycyclic armatic hydrcarbns (PAHs) arepresented in Table 1.1. Tstudy these spatial variatins f cntaminant cntents intplayer sediment, differences in srptin affinity f theparticles shuld be accunted fr. This can bedneby standardizatin with respect t the cntents f the different absrbing cmpnents in sediments. In this chapter nrmalized cntaminant cntents (crrected amunts) are calculated using clay and rganic matter cntents at each lcatin (Dutch standards, seefr calculatin methdlgy Chapter 3).Inmstchapters f thisthesis, except Chapter 2, 5and 8,nrmalized cntaminant cntents are presented. Lake Ketelmeer (38 km 2 ) wascreated as awide river muthbetween twcnstructed plders.the dike at its present nrthern bundary was cnstructed in 1938 and the suthern ne in 1953.It is the first sedimentatin basin f the river IJssel, anrthern branch f therhine.enrichment with nutrients and cntaminatin with heavy metals and rganic pllutants, is mainly caused by this river. It has slightly cntaminated sandy sedimentsin theeasternpartand severely cntaminated lamy sediments inthecentral andwestern part (WinkelsandVan Diem, 1990). Dredging fthis cntaminated material isfreseen fr thelamy sediments (IJm-depsits)inthenear future. Lake Ketelmeer has an pen cnnectin with Lake IJsselmeer, a large (1136 km 2 ), shallw eutrphic lake, with mainly sandy sediments and with high net sedimentatin rates f fine settling slids in its deeper parts (Vink and Winkels, 1991). The IJm-depsits cverthe deepest part, which is 25% f the IJsselmeer lake bed. Only these IJm-depsits in this lake are slightly cntaminated with mainly heavy metals.during the summer inlake IJsselmeer an internal prductin prcess is clearly reflected in an enhanced cncentratin f rganic matter and in the ccurrence f algal blms (Hgeveen, 1995).Nutrient cncentratins in the area are usually exceeding 0.1 g P m~ 3 and 2.2 g N m 3. These are typical Dutch standards which shuld be met, t have acceptable nutrient cncentratins in this lake (derijk, 1990).In general green algae make up mre than half f the bimass in Lake IJsselmeer (>100 mg m 3 chlrphyll-a), mainly Scenedesmus species. Mst ften blms f Micrcystis aeruginsaccur (Berger and Sweers, 1988). The Hutribdijk, separating Lake Markermeer frm Lake IJsselmeer, was cnstructed in Nwadays Lake Markermeer (680 km 2 ) is a shallw eutrphic lake with mainly lamy and clayey depsitsat the bttm. The IJm-depsitsarefund in thedeeper easternpartf this lake. Thesediments areingeneral ntcntaminated with heavy metals,pcbs rpahs (Winkels, 1994). Thewater quality f the lake, with respect t cntaminatin, phytplanktn blms and eutrphicatin, is gd, cmpared ttherlakesin the area (VanDuin, 1992). Prcesses inthe lake aredminated by the intensive resuspensin and subsequent settlingf sediment.this resultsin a highly fluctuating suspended slids cntent in the water, which isheldrespnsible fr the absence f blms suchasthsef Oscillatria agardhii inthis lake (Berger et al., 1986). Thes calledbrderlakesf Flevland (nrs. 1 t 8 in Figure1.1 ) are rathershallwandvaryin their physical characteristics frm ne lake t the ther. All kinds f sediments are fund here and annual nutrient input fluxes are mstly high, up t 30 g P m 2 and 90 g N nr 2 in Lake Eemmeer and Lake Gimeer (Berger, 1987). The sediments in these lakes are in general nt cntaminated with heavy metals, PCBs r PAHs (Vink and Winkels, 1996). Higher PAH-levels in the sediments are mainly fund inharbrs. Figures1.4and1.5 givean impressinfspatial variabilityf cntaminantsin this area.the figures are based upn the analysis f the tplayer (211 lcatins) in this area. Is-lines f nrmalized sediment cncentratins havebeen drawn inthesefigures, taking int accunt thelcatin f different 19

18 CHAPTER 1 Fig. 13. Thepresent-day tplayer sediments ( m)in thelakesf theijsselmeer area. 20

19 INTRODUCTION Legend Crrected amunt in mg/kg dm 11 < 2.0 IH > 12.0 ËB3 Sandpit r dredged parts shipping rute Fig.1.4. Thevariability f cadmium cncentratins in thetplayer sediments f thelakesinthe IJsselmeer area. 21

20 CHAPTER 1 Fig The variability in cncentratins f the sum f ten individual PAHs in the tplayer sediments f the lakes in theljsselmeer area. 22

21 INTRODUCTION sediment types in the area (Fig. 1.3). Figure 1.4 indicates that the river IJssel is the direct surce f heavy metal cntaminatin fr this area, as can be seen in the present spatial variability f cadmium cntaminatin. Figure 1.5 shwsthat besidesthe river IJsselalsthersurces (likeatmspheric depsitin and pint surces) are respnsible fr the cntaminant variability f XlOPAHs in this area. In Appendix 1 a gechemical characterizatin f the IJm-depsits in Lake Ketelmeer, Lake Usselmeer and LakeMarkermeer ispresented. Itshws that within this depsit the spatial chemical and cntaminantvariability inthe area ishigh. Outlinef thisthesis Chapter 2 describes theresults f sampling and analysis f aquatic sediments in Lake Ketelmeer, and the recnstructin f the histrical inputfcntaminants by theriverrhine.thelevelsf pririty pllutants (heavy metals, arsenic,pcbs andpahs)indated sediment cresfrm this lakeareused in this analysis. Area-specific gelgical time markers and radinuclide time tracers are used t establish present-day and histrical levels f pllutin since the late 1930s. Pstdepsitinal redistributin f pllutants and pssible transfrmatins areevaluated as well. In Chapter 3 the distributin and gechrnlgy f the pririty pllutants is described fr a larger sedimentatin zne, Lake Ketelmeer and Lake Usselmeer. The cntents f these cntaminants in the tp layerdiffer substantially due tdifferences in typefsediment betweenbthlakes. Therefre abslute cntentsare crrected hereaccrdingt a Dutchnrmalizatin prcedure. Furthermredilutinf theplluted suspended slids with lcal sediments inlakeusselmeer isdemnstrated. Frthis previus (frmer) sampling results and astudy f deeper cres in bth lakes isused. The infrmatin n the present cntents f pririty pllutants f depsits in the Rhine delta has increased during the last decades, but a cmparisn with ther majr Eurpean rivers has nt been madesfar. Chapter 4 presentssuch a cmparisn. Thesame gechrnlgical apprachf sampling, analysisanddatingcresamplesisapplied (Chapter2) here t recnstructhistric inputprfiles f pririty pllutantsin the deltasf the DanubeandVlgariver. Alsdifferences in cntaminant levelsduringthelast five decades between the Rhine,theDanube and thevlgadelta are discussed. In Chapter 5spatialstatisticsis usedtstudythe variability withincntaminated sedimentsf three znesin LakeKetelmeer. Applicatin fthisgestatistical apprach inanaquaticenvirnment is relatively new. These three znes are selected fr sampling, using prir knwledge f sediment type, sedimentatin/ersin znes,water depth and shipping rutes.optimal sampling distances fr assessment f the cntaminatin levels and f the thickness f the cntaminated layer in the sediments are estimated taking spatial variability in these znes int accunt. A new ptimal, cst-effective methd fr accurate aquatic mnitring is investigated as a preparatus step t the decisin making n the remval f cntaminants inthe future. Anther apprach fr recnstructin f pllutin histry is shwn in Chapter 6. Here als the insitucnslidatin f aquaticlakedepsits during severaldecadesinlakeusselmeer areais described. The subsequent lssfwater vlumein theseaquatic sediments due tcnslidatin isinvestigated t quantify this prcess. Measurements in sediment cres shwed that the heavy metal cncentratins in depsits frm the riverusselare 2t 3 timeslwerinlakeusselmeer thanneartherivermuth. Chapter 7 evaluates the effects f sedimentersin andprimary prductin n the tempéraiandspatialvariabilityftheheavy metals cncentratin in settling slids in Lake Usselmeer. It fcusses n the annual differences between histric inputf the river IJssel in theregin and the annual amunt f metals n settling slids attw lcatins inlakeusselmeer. Furthermre wind speed and directin and the suspended slids,rganic 23

22 Gechrnlgyf pririty pllutants inlake Ketelmeer, a sedimentatin areaf the river Rhine Abstract - Tplayer samples and subsequently three and eight sediment cres were taken frm Lake Ketelmeer, a sedimentatin area f the Rhine River, lcated in the central partf the Netherlands. Pririty pllutants (8 metals, 6 planar and mn-rth plychlrinated biphenyls and 8plycyclic armatic hydrcarbns) were determined in all r in a selected number f samples and cres. Present-day and histrical levels f pllutants since the late 1930s were established thrugh the use f radinuclide time tracers ( 137 Cs, 134 Cs) and areaspecific gelgical time markers. Pstdepsitinal redistributin f pllutants and pssible transfrmatins were evaluated by analyzing sediment tplayer samples that were taken in Disappearance in the anaerbic sediment was bserved fr several chlrinated biphenyls. Fr the metals and plycyclic armatic hydrcarbns trends in the cncentratin prfiles during the last five decades are described. Rather lw cncentratins f almst all studied chlrinated cmpunds were bserved in the early 1940s. These lw levels were in cntrast tthe metal and PAHcncentratins, which were already high in the late 1930sbut decreasedduring thesecndwrldwar. Frallstudiedcmpunds, maximum cncentratins were fund between 1955 and 1975.Cadmium and nickel levels remained high until Recently depsited sediments shwed lwer pllutant levels. The levels f lead, arsenic,and all studied PAHswere thelwest bserved in thepast five decades. Intrductin A wide range f chemical substances, including heavy metals, radinuclides, plychlrinated biphenyls (PCBs) and plycyclic armatic hydrcarbns (PAHs)can bedetected in natural aquatic envirnments.thesepllutantsriginatefrm avarietyf directandindirectsurces.thehigh affinity fthesepllutantsfrparticleswithinthewaterclumnresultsinrelativelyhighpllutinlevelsfthe suspended slids.wherestreamvelcities decrease,fr exampleinthelwerstretchesfrivers,the suspendedslidssettlewiththeassciatedpllutants.oncedeliveredtthebttmsediments,particle andpllutantburialwillbeaffected byresuspensinandbiturbatin.sedimentmixingbyzbenths atthesediment-waterinterfacemaylwerpllutantcncentratinpeaksanddistributepllutantsvertically,ascanbebservedinsedimentcresfrmareaswithhighbilgicalactivityandrelativelylw sedimentatinrates (Rbbins,1982). Otherprcessessuchasmleculardiffusin, transprtwithinfiltrating water, and bitransfrmatin f the rganic pllutants, may als alter the pllutant prfile recrdedinthesediment. Dated sediment creshavetheptentialfr prviding detailed chrnlgiesf pllutant inputas lngasbiturbatin, mleculardiffusin, transprtwithwaterandbitransfrmatin are (rmaybe cnsideredtbe)negligible.basedndatedsedimentcres,thedepsitinalhistryfmetals, PCBs, PCDDs,PCDFs,andPAHshasbeendcumentedfrtheNrthAmericanGreatLakes (Förstnerand 27

23 CHAPTER 2 (Um) depsit, is defined as the silty sediment depsited since The underlying Zuiderzee (Zu) depsit, a saltwater clay depsit, can be identified by the presence f shellfragments (Mya arenaria). The average thickness f the IJm-depsit is 0.45 m. The net sedimentatin rate (presently apprximately 0.01 m per year) has dubled since 1953 and accelerated depsitin ccurs in deeper znes (Winkels et ai, 1990). Tplayer samples, samples f the ttal IJm-depsit and samples f the Zudepsitwere takenevenly spreadver the centraland western partfthe lake. Thesedimentcreswere taken at lcatins knwn fr their thick IJm-depsits. The majrity f Lake Ketelmeer sediment is anaerbic;nlythetplayer (1-3 cm)attheinterface with thewater isaerbic.chemical characterizatin f the IJm-depsit indicates that illite is the dminant clay mineral (60% w/w),with smaller cntributins f mntmrillnite (20%w/w) andkalinite (20%w/w) (Rijniersce, 1983). Sample cllectin and treatment In 1987 attwenty different lcatins tplayer (0.15 min diameter and average length 0.1 m) and ttal samples (0.15 m in diameter and average length 0.45 m) f the IJm-depsit were taken with an pen auger (Fig. 2.1).Atfive ftheselcatins alstheunderlying Zu-depsit was sampled (0.15 min diameterand length 0.05 m).in certain areasflakeketelmeer thegelgical,chrnlgical sedimentatin sequence isdisturbed by sandpits, which were dug t gain sand fr rad and dike cnstructin in the plders. Here accelerated depsitin f the IJm-depsit ccurs, since the mment these pits were created. In three f these sandpits, created in 1960, 1966and 1986 (Fig. 2.1),respectively, cres were takenwithanpen auger.these cres, cntaining IJm-depsits nly,were sectined intfur, fiveand twdepth intervals,respectively. Subsequently, in 1988and 1990 eightundisturbed sediment cres (0.15 min diameter and average length f apprximately 1 m) were taken with an pen auger (Fig. 2.1). These cres, als cntaining mainly the IJm-depsit, were sectined int0.05 t0.10 mintervals. Onef these cres,taken frm a frmer sandpit (created in 1938),was sectined int0.25 mintervals.atthis lcatin thethicknessf theijm-depsit was abut 4.2m. All sampleswere putin glass jars with screw caps, refrigerated at 4 Candtransprted. Befre subsamples were taken fr thedifferent chemical analyses, samples were freeze dried and hmgenized. Finally sediment tplayer samples (0.05m)frm 1972were cllected by the Institute fr SilFertilityResearch, Haren, the Netherlands.The 10 samplestakenin 1972 riginatefrm thesameareasas theeight sediment cres takenfr thisstudy.after cllectin in 1972, thetplayer samplesweredried vernightat 40 C andstredin jarswithscrewcapsat rmtemperaturein thedark. Lssesf rganic pllutantsduringthedryingprcedurewere negligible (Japenga et al.,1990).in these tplayer samples nly sme heavy metals were determined sn after cllectin. Tgether with all ther samples the rganic pllutants weremeasured in thesetplayer samples frm Sediment dating The age f the twenty tplayer samples and f the twenty samples frm the ttal IJm-depsit are nt knwn a priri,but tplayer samples arethught trepresent recent depsitin f cntaminatin. The age f the different layers in the sediment cres was estimated by several methds. First, the well knwn gelgical histry f this area ffers sme valuable recgnitin pints in the cres. The interface between Zu-depsit and IJm-depsit is visually recgnizable and indicates the early 1930s. Until 1953, when the suthern dikef Lake Ketelmeer wascmpleted, sedimentatin ccurred ver a muchlargerarea. As a result,nly a thinsedimentlayer representsthe peridf 1930 t Thecre samples frm the frmer sandpits, represent sediment depsited after the mment they were created. These sandpits act as sediment traps with high sedimentatin rates (apprximately 0.15 m per year). Secnd, l37 Cs and 134 Cs gamma activities were determined n 25 t 250 cm 3 f freeze dried cre 30

24 GEOCHRONOLOGY OF PRIORITY POLLUTANTS IN LAKE KETELMEER sedimentbycunting up t 1000min with a caxial G detectr (P-type)cupled t a multichannel analyzer.thecanberra S340 DOS/SPECTRAN-AT applicatin sftware packagewas usedfr peratin f the system and analysis f the recrded gamma spectra. Third, heavy metal cncentratins in sediment layers were related tthe well knwn metal pllutin histry f therhine River.Theusef the 210 Pb-dating technique (Rbbins and Edgingtn, 1975) prved t be prblematic in these cres, prbably due t high and variable discharges f 210 Pb rmther nuclides ( 226 Ra) in therhineriver. Analysis f rganic carbn and heavy metals Therganiccarbn cntentf thesediment sampleswasmeasured byanelement analyser (CarlElba NA 1500, Milan,Italy) after remval f carbnates with phsphric acid. Heavy metal cntents f the freeze-dried sediment cre samples were determined after sample treatmentwith strng acids: hydrchlric acidfr Cdand Pb, a mixturef sulfuric acid, nitricacidand hydrgen perxidefr As,Cr, Cu, Ni,and Zn;and a mixturef sulfuric acid,nitricacid,andptassium persulfate fr Hg.Cadmium, Cr, Cu, Ni and Pb were analyzed by graphite furnace atmic absrptin spectrmetry (Perkin Elmer5000, Nrwalk, CT). Zincwasanalyzedbyflame atmic absrptin spectrmetry (Perkin Elmer 5000). Arsenic was analyzed using the hydride technique (Perkin Elmer MHS1) and Hgby amercury mnitr (Miltn Ry,HGM 2300,Rchester, NY).Tplayer samples and samples f the ttal IJm-depsit were analyzed fr heavy metals using a similar apprach as described byhfstee (1983). Zinc,Cu, Cd,Pband Cr cntentsinthe tplayer samplesfrm 1972 were determined at the Institute fr Sil Fertility Research by similar analytical methds (Japenga et al., 1990). Analysis fpcbs Seven PCBs,i.e.PCB 28,PCB 52,PCB 101,PCB 118,PCB 138, PCB 153andPCB 180 were determined in alltplayer and ttal IJm-depsit samples and in thethree sandpit cres (all sampled 1987). These PCBswere analysed accrdingthemethdlgy describedbyvan ZestenVan Eck (1990).Six mnandplanar PCBs (sampled in ), i.e.pcb 77, PCB 105, PCB 118, PCB 126, PCB 156, andpcb 169wereanalysedinall layersfthreeselectedcresand infivetplayersamplesfrm Latter analyses were perfrmed in cmbinatin with analyses f PCDDs and PCDFs. Sediment sample clean-up and analytical prcedures were adpted frm the literature (Smith et al., 1984; Rappe, 1984),hwever, smeminr mdificatins were applied asdescribed by Beurskens et al. (1993). The extractswereanalyzed bygc/ms (Hewlett Packard ,Avndale,PA)perating in the selectivein mnitring (SIM) mde. Theplanar and mn-rth PCBs were analyzed with a 60 m capillary clumn (SE 30,0.25 mmi.d., film thickness 0.25 ftm). Analysis fpahs ThePAH cmpundsevaluated in this studyincluded fluranthene (Flu), benz[k]fluranthene (BkF), benz[a]pyrene (BaP), flurene (Fie), benz[b]fluranthene (BbF), anthracene (Ant), phenanthrene (Phen), benz[ghi]perylene (Bghi) and indenpyrene (Ind). Sediment samples were extracted twice with acetne fr 15 min. Acetne was remved by mixing the extracts with petrleum ether and washing them with water. After separatin, the aqueus phase was extracted with a secnd prtin f petrleum ether.the cmbined petrleum ether extract wasdried with Na 2 S0 4 and cncentrated with akuderna-danish cndensr (Technglas,Vrhut,the Netherlands) t a vlumef 5 ml. Theextract vlume was further reduced with agentle stream f clean nitrgen t 1 ml.extract cleanup cnsisted fpassing the extractthrugh aclumn f 2 g 11% (w/w)deactivated alumina (alumina W200, Super IWelm, ICN, Enschwede,Germany)andthrugh a clumnf 2 g6% (w/w)deactivated silica (Merck 7754, Darmstadt, Germany).After sample cleanup a slvent exchange t acetnitrile was carried ut. 31

25 CHAPTER 2 The sample extracts were injected int an HPLC (Perkin Elmer pump 250 and Spark Marathn autsampler,emmen,the Netherlands) fitted with a25cmvydac201 TP-5clumn (4.6 mmi.d.). The extracts wereeluted iscratically fr 5min with 50% (v/v)acetnitrileinwaterand subsequently with a linear gradient t 100%acetnitrile in 15 min. The mbile-phase flw was 1.5 ml/min. The clumn effluent was mnitred with a flurescence detectr (Perkin Elmer LS40) and a UV-detectr (Krats 783, Krats Analytical, thenetherlands). All cncentratins f radinuclides and pllutants are reprted n a per-dry-weight-f-sediment basis.cncentratins f pllutants have ntbeen crrected accrding t a Dutch nrmalizatin prcedure as described in Chapter 3f this thesis.nrmalized results wuld give similar results t theraw data presented here, because Urn-depsits in Lake Ketelmeer have arather cnstant clay and rganic matter cntent. Frthisreasn and tcmpare the results f thischapter with Chapter 4, wechset present nly abslute cntents f cntaminants in these tw chapters. Fr purpses f numerical calculatin and graphical display, all cncentratins belw detectin levels were assumed t be ne-half the detectin level. Resultsand discussin A.Sampling in 1987 Cntaminatin Urn- and Zu-depsits Table 2.1 givesaveragevalues, rangesand standard deviatinsfr heavymetals, PCB s andpahsinthe IJm-and Zu-depsits. Zu-depsits cntainsignificantly lessheavymetalsand PCBsandPAHs thanthe IJm-depsitinthislake (Mest P <0.05).In thezu-depsits themetal cncentratins were inthe same range as natural backgrund levels (Salmns, 1989).This indicates that during the depsitin f the IJm-depsit (last 60 years) dwnward transprt f heavy metals, PCBs and PAHs with infiltrating water is insignificant. Table 2.1. Cncentratin levels f pririty pllutants in tplayer and ttal IJsselmeer-depsit (Um lp, Um 101 )and in the underlying Zuiderzee-depsit (Zu). Um tp Um, 0l Zu Natural 1 Range Av. Sd Range Av. Sd Range Arsenic (mg/kg) Cadmium (mg/kg) Chrmium (mg/kg) Cpper (mg/kg) Mercury (mg/kg) < Lead (mg/kg) Nickel (mg/kg) Zinc (mg/kg) l7pcbs 2 (Mg/kg) <50 I6PAHs 3 (mg/kg) <0.2 1 Natural backgrund levels;surce Salmns (1989) 2 PCB-cngeners (IUPAC n.): 28, 52, 101,118, 138, 153 and PAHs:fluranthene, benz[k]fluranthene, benz[a]pyrene, benz[b]fluranthene, benz[ghi]perylene and Indenpyrene 32

26 GEOCHRONOLOGYOFPRIORITYPOLLUTANTSINLAKEKETELMEER Table2.2. Cncentratins f heavy metals, PCBs andpahsinthe IJsselmeer-depsitf three sandpits atdifferent depths. As Cd Cr Cu Hg Pb Ni Zn PCB28 PCB118PCB180 Hu BaP Bghi Sandpit m m Sandpit m m m m m Sandpit m m m m m Thetplayer f thedm-depsit (IJm tp )cntains significantly lessheavy metals, PCBs,andPAHs than the ttal IJm-depsit (IJm tt ) at the same lcatin in Lake Ketelmeer (Mest P < 0.05). The bservedpriritypllutantcntentsin IJm tp are inagreementwithcncentratinsfund infld plain tplayer samples (Japenga et al.,1990)andrecentmnitring results (Heymen, 1990).Cncentratins in IJm tt indicate thatcncentratins fr thesepriritypllutants werecnsiderably higherbefre than they arenwadays. Cntaminatin changes in three sandpits InTable2.2 cncentratins f heavy metals,threepcbs and threepahsin theijm-depsitsaregiven atdifferent depths in the sandpits created inlake Ketelmeer in 1986, 1966and 1960,respectively. Theyungest sandpit cntains thelwest cncentratins f allcntaminants.cntaminatin levels f allpririty pllutants increase with depth in sandpit 1966.Inthe deeper parts f the sandpit created in 1960 cncentratins stablizer decreasefr cadmium, chrmium, cpper, mercury, lead andinvestigated PCBs.Frevery cntaminant thecncentratin inall sandpitscanbe cmbined anddrawn int negraph; this crrespnds with acncentratin prfile fr thiscntaminant during the last 30 years. Figure 2.2 shws nef thesecncentratin prfiles fr PCB 118.The degree f cntaminatin inthe IJm-depsit isclearly decreasing during the lastdecade and was substantially higher in the sixties and seventies, which is in agreement with recent mnitring results (Heymen, 1990) and with cncentratinsfund inriverfld plain samples ver thelastthree decades (Japenga et al., 1990).Hence,high vertical cntaminant variability ccurs intheijm-depsits flake Ketelmeer. B. Cresampling in Radicesium activities Inall cres,activityf 137 Cs (t ]/2 = years)shwedtw maxima.one 137 Csmaximum,in the sam- 33

27 CHAPTER Depth (m 1! I. ' I, l I i i i PCB 118 cntent fg/kg dry mat.) Figure 2.2. Plychlrinebiphenyl (nr. 118) cncentratin atvariusdepths intheijm-depsitf threesandpits (different ages) inlake Ketelmeer. piesfrm near the surface, always crrelated with elevated activities f 134 Cs (t 1/2 =2.06 y),indicating the fallut frm the nuclear pwer plant accident inchernbyl inapril The secnd 137 Csmaximum, fund in the deeper layers, was related t the fallut frm nuclear weapn testing in the early 1960s.Besides the radicesium activities, several ther markers were used t estimate the age f the different layers. The visually recgnizable interface between the Urn- and Zu-depsits indicated the year 1932.In the cre taken frm the frmer sandpit, this interface represented the year 1938.Heavy metal cncentratins in sediment layers were cmpared tpllutin levels in dated sediment samples frm ther lcatins in the Rhine (Salmns and de Grt, 1977). Based n this infrmatin, the sediment cre layers were dated int perids that varied between tw and ten years.the depth f the IJm-depsit in the varius sediment cres varied between 25 and 420 cm, indicating highly variable sedimentatin rates. If sedimentatin rates are nt identical, graphic presentatin f radinuclide activities r pllutant cncentratins pltted against depth is pssible nly fr the individual cres. Hwever, after age estimatin f the different layers, data frm all cres can be cmbined int ne graph pltted t the estimated year f depsitin instead f depth. This methd f data handling can intrduce sme inaccuracy.biturbatin rtransprt withinfiltrating water will have lesseffect n sedimentcre pllutantprfiles at a lcatinwith high sedimentatin rates than at lcatinswithlwsedimentatin rates (Eisenreich et al.,1989). 34

28 GEOCHRONOLOGY OFPRIORITY POLLUTANTS INLAKEKETELMEER Activity ( in Bq/kg) Year f dépsitin Figure 2.3. Cesium activities in sediment layers frm 8 cres vs.the estimated years f depsitin. Average activities areindicated by visually fitted curves. In Figure 2.3, Cs activities are pltted against estimated year f depsitin. A certain amunt f variatin in activities can be bserved, especially in the 137 Cs activity f the near surface samples. Nevertheless, a clear pattern in Cs activities during the last five decades can be distinguished and is indicated by the visually fitted curves. Organic carbn The rganic carbn (OC) cntent f suspended slids and sediment plays an essential rle in the behavir and fate f pllutants in the aquatic envirnment (Capel and Eisenreich, 1990). Mineralizatinprcessesaffect therganicmatterinsediments.if a cnstant inputfoc hasccurred in the past, a decreasing OCcntent may be expected at increasing depth in the sediment. In Lake Ketelmeer the OC cntent in the layers f the sediment cres varied widely (Fig. 2.4A). Surprisingly, the recently depsited layershave thelwestoc cntent.the highest levelsarefund in layersthatweredepsited between 1950 and TheOC cntentfthe tplayer samplestaken in 1972 isalsshwninfigure 2.4A. Because these 5 cm tplayer samples prbably reflect an average sediment cmpsitin fr a fur t six year perid, they are put in the graph at 1969.The average OC cntent f these samples is smewhat higherthan theoccntentin the crelayers datedarund Thisdifference indicates a small decrease in the carbn cntent f the sediment, which is prbably the result f mineralizatin. Benthic prcesses in the sediment samples frm 1972 have been interupted (by drying the samples). Hwever, theinfluence fther prcesses like resuspensin, internalprductin andbiturbatin can- 35

29 CHAPTER 2 10 Percentage A: Organic Carbn Cncentratin (in mg/kg) Year f depsitin Year f depsitin Cncentratin (in mg/kg) 1000 ; D Cncentratin - Chrmium D/ in mg/kg) sy 1 ^Sf- 0 D id D \ \ D \H D D Nickel O Oy 'O O Q^e % e O O BO O A O Year f depsitin i I i I i, i 1, 1, Year f depsitin Figure 2.4. Organic carbn cntent (A) and metalcncentratins (B,C,D) in sediment cre samples (O, G, A) and in tplayer samples frm 1972 (,, ) vs. the estimated years f depsitin. The average cncentratins in sediment cre samples are indicated by visually fittedcurves. 36

30 GEOCHRONOLOGY OF PRIORITY POLLUTANTS IN LAKE KETELMEER nt be excluded. The internal OC prductin in Lake Ketelmeer (apprx. 1 gc/m 2 jaar) is abut 0.25% f theoclad f the river (Pers. Cmm. Rijkswaterstaat). The steady decrease in the OCcntentsince 1960 is directlyrelated t a decreasefthe ttalocladinthe RhineandIJsselrivers (Internatinal Cmmissin n Prtectin f Pllutin f the River Rhine, 1989). This decline prbably resultsfrm the cnstructin fwastewatertreatmentplantsin the drainage basinf the Rhinesince the 1960s. Heavy metals The cncentratin prfiles f eight heavy metals are als shwn in Figure 2.4.Under the anxic cnditins prevailing in Lake Ketelmeer sediments, heavy metals are relatively immbile and, therefre, heavy metal prfiles are likely t reflect the histric inputs. The 1972 tplayer samples ffered an pprtunity t test this assumptin. The cncentratins f sme metals in these ld tplayer samples are shwn in Figure 2.4. The levels in the tplayer samples frm 1972 were smewhat higher, especially fr Cd and Cr, than the levels fund in the cre layers dated arund This difference may have been caused by deviatins in the analytical methds, as heavy metal cncentratins in sediment cres and in tplayer samples frm 1972 were nt determined by the same labratry. In additin, the decrease in metal cncentratins in the sediment cres may have been caused by resuspensin and biturbatin. The 1972 tplayer samplesreflected levelsthatmayhavebeen lwered afterwards by these prcesses.basednthe limitedchangesbservedbetweenheavymetalcntentsin thecre samples andtplayer samplesfrm 1972 the impactf these prcesses seemslw,and,therefre, theprfiles reflect thehistric inputs withut serius alteratins. Allheavy metallevels werevery lw between 1940 and Thecncentratins at the endf the 1930s appeared t be higher than the cncentratins in the early 1940s (Secnd Wrld War). Frm 1950 t 1965 all the studied heavy metals shwed a steady increase in cncentratin. Fr all metals except Cd and Ni, a clear decrease frm abut 1965was bserved. Cadmium and Ni levels started t decrease sincetheearly 1980s.Intherecently depsited sediment heavy metal levels wereeither similar (Zn, Cu, Hg, and Ni) r belw (Pb and As) the levels bserved in the 1940 t 1950 perid. Presently, Cd and Cr levels are still smewhat higher than the levels in the 1940 t 1950 perid. The bserved patterns in metal cncentratins arein agreement with cncentratins fund in Rhine River fld plain samples verthe last threedecades (Japenga et al.,1990). Thedatafrm thenndegradable,relatively immbile metalsindicate that resuspensin andbiturbatin havehad nly limited effects nthepllutant prfiles. Cnsequently, cmbinatin f data frm all dated cres int ne graph appeared t be a feasible and elegant methd t interpret the results. Hwever,ther prcesses,suchasdiffusin and transprt withinfiltrating water,mayhaveaffected the cncentratin prfiles f sme mbile rganic pllutants, like di- and tri-chlrbenzenes (Zwlsman, 1992).Hwever, thecncentratins f the selected PCBs (Table2.2) wereall belw thedetectin limit (10ng/kg) inthezu-depsit, indicating that ndwnward transprt had ccurred. Plychlrinated biphenyls The cncentratinsffur PCBsareshwnin Figure 2.5. The cncentratinprfile frpcb 118 (Fig. 2.5 C) is similar tfigure 2.2 fr the perid The average PCB 77 and PCB 118levels in the samples frm 1972 are smewhat higher than the levels fund in the sediment cres. This difference between thestred 1972samplesand sediment cresiseven mre prnunced fr PCB 105 and PCB 156.The difference in cncentratins between tplayer samples frm 1972 and cre layers that had been depsited arund 1970 weretested fr the six studied PCB cngeners (Table2.3). The differences prved t be significant at a0.05 level fr all tested cngeners, exceptfr PCB 77 and PCB 118. Significant reductins varied between 70 and 88%. These reductins indicated that 37

31 CHAPTER 2 Cncentratin ( 7000 A.PCB77 n ng/kg) Cncentratin (in ng/kg) S: PCB : : / / c K '""-~ I %^sé. W,.,., N \> 0 i.. baqft l i, i Year f depsitin Year f depsitin Cncentratin (in ng/kg) C: PCB Cncentratin (in ng/kg) D: PCB s/ *\ O ç, -^fi>t\, i, i, ' \ Year f depsitin Year f depsitin Figure 2.5. Cncentratins f 3,3',4,4'-tetrachlrbiphenyl (A), 2,3,3',4,4'-pentachlrbiphenyl (B), 2,3',4,4',5-pentachlrbiphenyl (C)and2,3,3'.4,4',5-hexachlrbiphenyl (D) j n sediment cre samples (O) andintplayer samples frm 1972 ( ) vs. theestimated years f depsitin. Theaverage cncentratins in sediment cre samples areindicated by visually fitted curves. 38

32 GEOCHRONOLOGY OF PRIORITY POLLUTANTS IN LAKE KETELMEER Table 2.3. Cmparisn f mean PCB cncentratins in tplayer samples (n =5) cllected in 1972 and mean cncentratins in recently sampled cre layers (n =5)depsited arund Cncentratin (ng/kg) PCB (1UPAC n.) Tplayers cllecte 3, , , , Sediment crelayers frm ±1970 Reductin (%) ' 1,540 33, , , Numerical values aregiven fr decreases that are significant by thef-test at the0.05 cnfidence level. PCBs have disappeared frm the anaerbic lake sediment, which may be the result f micrbial dechlrinatin prcesses in theanxic sediment. Ithas been established that disappearance f higher chlrinated biphenyls in the Hudsn sediment (Brwn et al., 1987a and 1987b) is a result f micrbially mediated reductive dechlrinatin reactins (Quensen et al.,1988and 1990). Unlikethe studies inthehudsn, wewereunabletdemnstrate an accumulatin freactin prducts like lwerchlrinated biphenylsin Lake Ketelmeer sediment, due tthe limited numberf cngeners analyzed. If thefindings in Lake Ketelmeer can be attributed t micrbial prcesses, this typef dechlrinatin seems t alter the cncentratins f the individual cngeners at different rates;pcb 77 and PCB 118 seem t be the mst recalcitrant cngeners. The ther fur PCBs shw an average reductin f 80% during 20 years f "envirnmental incubatin". Assuming first-rder kinetics fr the micrbial prcesses, ahalf-life f nine years can be estimated fr these PCBs in the anaerbic Lake Ketelmeer sediment. Althugh the rigin f the bserved reductin remains uncertain, it hasbeen demnstrated clearly that the cnstructed cncentratin prfiles f the planar and mn-rfh PCBs in Lake Ketelmeer sediment underestimated the histric inputs.despite the substantial reductins, peaks inpcb prfiles culd still be recgnized. The present pllutin levels in the sediment layers are characterized as fllws (shwn partly in Fig.2.5).Thecncentratins f the planar PCBs (77, 126,and 169)werebelw r just abvethedetectin limit (10 ng/kg)insediment layersfrm theearly 1940s.Onthetherhand, themn-rth PCBs (105,118, and 156)hadelevated levelsin theselayers.ingeneral,pcbcncentratins shwed arapid increasefrm sediment layers dated arund 1950and reached maximum cncentratins inlayersfrm the 1960sand 1970s. Asimilarpatternhasbeenreprted fr PCBs in stred Rhine Riverfldplain samples,withhighest cncentratins intheearly 1970s (Japenga et al, 1990). Inrecently depsited sediments,cncentratins fpcb 126andPCB 169 wereagainbelw the detectin limit. Recent pllutin levelsf PCB 77 were still elevated, ascmpared t thepllutin levelsin layers frm the 1940s. The recent cncentratins f the mn-rth PCBs (105, 118, and 156) were relatively lw and similar t the cncentratins in layers frm the early 1940s.Cncentratins started t decreaseafter abut This decrease startedbefre anfficial PCBban wasintrduced in Eurpean cuntries.theprductin f PCBs in therhine area stpped in 1983, and usageingerman cal mineshasbeen prhibited since 1985 (Friege et al, 1989)

33 CHAPTER 2 alteratins, the histric inputs during the past five decades. The pllutin histry is characterized as fllws: - Lw cncentratinsfmetalswerebserved intheearly 1940s,PAHs levelswere already elevated. Fr bth metals and PAHs, sediment cres presumably reflect a reductin in emissins during the Secnd WrldWar. - Highestlevelsf metalsandpahs werefund between 1955and Cadmium andnickellevels remained high until Recently depsited sediments had rather lw levels,smef which werethe lwest ever bserved during thelast five decades (Pb,As,all studiedpahs). Almst all chlrinated cmpunds shwed smedisappearance inthe anaerbic sediment, as cmpared t the levels in stred 1972 tplayer samples that reflected the riginal pllutin input. Fr several PCBs this disappearance prved t be significant and may have been caused by micrbial dechlrinatin reactins in the anaerbic sediment. Cnsequently the cncentratin prfiles f the chlrinated cmpunds d nt reflect the riginal pllutin histry. Despite these disappearances, peaksinpcb cncentratinprfiles arestillbserved.presently, the fllwing trendsincncentratins f PCBscan be bserved inlake Ketelmeer sediment: - Almst all studied PCBshad rather lwcncentratins intheearly 1940s. - Highest levelsf PCBs werefund between 1960and Recently depsited sediment has elevated levels f PCBs, as cmpared t the levels in the layers frm theearly 1940s. The verall picture indicates that the recently depsited material is far less plluted than the sedimentdepsitedinthe 1960s and 1970s. These findings suggest that highly plluted sediments frm thepast areburied under aless plluted layer. Hwever, the lcatins selected in this study have high sedimentatin rates and may differ frm ther lcatins. Altered sedimentatin rates ccur near shipping rutes where resuspensin is high, r in harbrs, where frequent dredging activities remve recently depsited material. At these lcatins the highly plluted sediment layers may remain uncvered and theaquaticrganismsmaystillbe expsedt thehighlyplluted sedimentfrm the 1960s and 1970s. Acknwledgements We thank G.A.J. Ml, H.L.Barreveld and B. vanmunster (allfrm the Institute f InlandWaterManagement and Waste Water Treatment, RIZA) fr their cntributins t the riginal manuscript f this paper. We thank Mr. H. Wijkstra (Institute fr Sil Fertility Research, Haren, the Netherlands), wh kindly prvided the Lake Ketelmeer tplayer samples frm 1972, and Drs. D.H. Meijer and Mr. P.W.M. Wijers (TAUW Infra Cnsult, Deventer, The Netherlands) fr the analyses f PCBs in the sediment samples. 42

34 Chapter 3 Distributinandgechrnlgy fpririty pllutantsin alargesedimentatinarea,riverrhine, thenetherlands HJ. Winkels,J.P.M. Vink,J.E.M. Beurskens and S.B. Krnenberg based n: Winkels, H.J., J.P.M.Vink, J.E.M. Beurskens and S.B. Krnenberg Distributin and gechrnlgy f pririty pllutants in a largesedimentatin area,riverrhine,thenetherlands. Appl. Gechem. Sup. 2:

35 CHAPTER 3 Nrmalizing the metal cntents accrding t this methd seems adequate. The absrptin (capacity) due t cntent f clay minerals, rganic matter and Fe-Mn-(xy)-hydrxides is taken int accunt. Irn- and Mn-(xy)-hydrxides are thught t be assciated with the clay fractin (Kelmans andlijklema, 1992). If therganic matter cntentf asample is > 30% r < 2%,these tw percentages havet beused inthecrrectin prcedure. Organicpllutants werecrrected accrding t: With: Y = Crrected rganicpllutant cntent (mg/kgdry matter) X = Abslute rganic pllutant cntent (mg/kg dry matter) O = Organic matter cntent (%) 10 Y = X- - (2) Nrmalizing abslute cntents in the IJm-depsit generally result in 15% higher values, as a cnsequencef alwaverageclaycntentin bthlakes.frthemainly sandy sedimentsflake IJsselmeer the crrected values are in general 60% higher due t lw rganic matter and clay cntents. Values lwerthan the detectin limits can ntbenrmalized with this methd. Results and discussin Recent surficial sediments The thickness f the IJm-depsit was determined at every sample site using an pen auger (s called Vrij-Wit-auger). In LakeIJsselmeer, thick layers (> 3m)f this depsit were fund in thedeeper central zne. In Lake Ketelmeer this depsit is absent in the east, where a nn-cntaminated sandy delta ccurs.atthemuthf the river IJssel,thicklayersfthis depsit (> 1 m)arefund. In the entirecentral and western part f thelake smaller amunts f theijm-depsit arepresent. The surface samples f the IJm-depsit, including wrm burrws and munds, appear t remain undisturbed with the Jenkins mudsampler. In Fig.3.2 the IJm-depsit isindicated by agrey tne. Table3.2gives thenrmalizedmeancncentratins (includingstandarddeviatin)frall priritypllutantsandthercmpundsin the recent (previus5-10a) IJm-depsitin bthlakesand theldersandy surficial layer in Lake IJsselmeer. These mean values and standard deviatins are based n data f apprximately 25 t 30different samplesites, exceptfr thepahs wherenly 15 samplesites were used. Clay and rganic matter cntents in the IJm-depsit are similar in bth lakes. The rganic matter cntentfthe IJm-depsit is highlyvariable in Lake IJsselmeer,whichmight berelated t the highcarbnate cntents in the sediment f this lake. In general, high carbnate cntents are cnsidered t be theresult f increased prductin due talgaeblms inthiseutrphic lakein the summer (Salmns and De Grt, 1978).Algae cnsumptin f C0 2 enhances theph f the water and results inprecipitatinfcalcite (DelCastilhand Salmns, 1986). Algaeblms are cmmn inlakeijsselmeerbut haveneverbeen encuntered inlake Ketelmeer. The distributin pattern f nrmalized Pb in surficial sediment f bth lakes is shwn in Fig Resultsindicate that Pbis distributedfairly unifrmly ver LakeKetelmeer.InLake IJsselmeerPb cntentsf the surficial sediments are timeslwer.here theamuntf Pbfllws the pattern f the IJm-depsit inthis lake. Thesepatterns areindicativefr all studied pllutants. Heavy metal andas cntentsfthe IJm-depsit arein Lake Ketelmeer timeshigher thanin Lake IJsselmeer. There is als a significant difference (factr 2-4) between the cntents in the lder 48

36 DISTRIBUTION AND GEOCHRONOLOGY OFPRIORITY POLLUTANTS IN ALARGESEDIMENTATIONAREA scale 1: '"J"», V / Lake Ketelmeer Fig Nrmalized Pb cntents (mg/kgdry matter)insurficial sedimentsflakeketelmeerandlake IJsselmeerin theperid

37 CHAPTER 3 Table 3.2. Mean nrmalized cntent(x) and standard deviatins (a) fr several pririty pllutants and ther cmpunds inthe recent ( ) surficial sediments (IJm-depsit andlder sandy sediments)in Lake Usselmeer and Lake Ketelmeer. Lake Usselmeer IJm-depsit Sand Lake Ketelmeer IJm-depsit X X a X a Clay frac, cntent (%) Org.matter cntent (%) CaC0 3 cntent (%) ± ± ± 4.1 ± 1.5 ± 1.7 Metals (mg/kg dry matter) As Cd Cr Cu Hg Pb Ni Zn ± + ± ± + + ± ± ± + + ± + + ± ± 3 ± 7 ± 58 ± 34 ± 0.5 ± 52 ± 5 ± 406 Plychlrinated biphenyls (ag/kg dry matter) PCB 28 PCB 52 PCB 101 PCB 118 PCB 138 PCB 153 PCB 180 Sum 7 PCBs ± ± ± ± ± ± ± ± * 2.8* 2.8* 2.8* 2.8* 2.8* 2.8* 19.3 ± ± ± ± ± ± ± ± ± 24 ± 20 ± 15 ± 4 ± 16 ± 12 ± 6 ± 63.7 Plynuclear armatic hydrcarbns (mg/kg dry matter) Fluranthene Benz(k)fluranthene Benz(b)fluranthene Benz(a)pyrene Benz(ghi)perylene Inden( 1,2,3-cd)pyrene Sum 6PAHs ± + + ± + ± ± ± ± ± ± ± ± ± ± ± * based n values belw thedetectin limits sandy sediments and theijm-depsit in LakeUsselmeer. The cntents f thelwerchlrinated PCBs in the IJm-depsit are eight times higher and the ther PCBs are just five times higher in Lake KetelmeercmparedtLakeUsselmeer, whereaspahsare2-9times as high. The cntents f rganic pllutants differ significantly (factr 1.5-3) between the IJm-depsit and the lder sandy depsits f Lake Usselmeer. The degreef pllutin decreasesin the Um-sediment depsitedfurther frm the river muth. 50

38 DISTRIBUTIONAND CEOCHRONOLOGY OFPRIORITY POLLUTANTS IN A LARGESEDIMENTATIONAREA scale 1: Lake Ketelmeer Plder Flevland Fig Nrmalized Pb cntents (mg/kgdrymatter)insurficial sedimentsflakeketelmeerand Lake IJsselmeer in theperid

39 CHAPTER 3 Older surficial sediments In Ente (1984) sampled surficial sediments inbth lakes fr afew heavy metals and ther cmpunds.thenrmalized meancncentratins (including standard deviatins)frtheheavy metals Cd, Hg and Pb in the IJm-depsit f Lake IJsselmeer are 5.2 (3.0), 1.5 (0.8) and 99 (35). Fr Lake Ketelmeer these cncentratins and standard deviatins are 25.6 (12.5),5.6 (2.8) and 305 (53).These values arebased n ~ 30sample sitesinlake IJsselmeer and 18 inlake Ketelmeer. The distributinpatternfnrmalized Pbinsurficial sedimentf bthlakesin isshwn in Fig.3.3. Absluteleadcntentsf Ente (1984)have beennrmalized anddrawninthisfigure, which cannw becmpared withfig.3.2. Resultsindicatethat Pbwasdistributedfairly unifrmly verlake Ketelmeer and the cntents in the surficial sediments were 1.9 times higher 10years befre. In Lake IJsselmeer Pb cntentsf thesurficial sediments were 1.7 timeshigherin HeretheamuntfPb alsfllwed thepattern f theijm-depsit inthe lake. In LakeKetelmeertheclayfractin, rganic matter andcarbnate cntentshaventchanged much ver the last 10a. Cmparing data f Ente (1984) t thse in Table 3.2, a slight decrease f the clay fractin cntent and an increase f thecarbnate cntent intime can benticed in Lake IJsselmeer. In the sandy part f LakeIJsselmeer, neither theheavy metal cntents nrthecntents f the ther cmpundshave changed ver the last 10a. Theheavymetal cntentsin the IJm-depsitf bthlakeswere tw times as high as they are tday. This phenmena crrespnds t the decreasing pllutin f the river Rhine,e.g. IJssel, during the last 10 a (VanGgh, 1988;Salmns and Eysink, 1981). The depsitin f the IJm-sediment in Lake IJsselmeer is still ccuring in the deeper parts f this lake. The physical cnditinsf bthlakes d ntseem t have changedmuch during the last 10a; bth are well-mixed freshwater lakes wherewind-induced resuspensin andsedimentatin (Ten Hulscher et al,, 1992; Lijklema et al., 1994) is fund in a clckwise flw pattern in Lake Ketelmeer (Tet and Blm, 1989)and reverse inlake IJsselmeer (Verhagen, 1988).Due thigh lads f N and P ver the last 10 ain Lake IJsselmeer, algaeblms have becme cmmn phenmena in the summer (Berger, 1987). Deeper cres Vink and Winkels (1991) givetheresults frm the cre sampled in eleven intervals at a deep lcatin (see *in Fig. 3.2) in Lake IJsselmeer. This area was anersive tidal sandy gully befre the enclsure Table 3.3. Water depths,changes in thickness f the IJm-depsit and calculated actual credepths and net sedimentatin rates during thelast60 ain a deeper znef Lake IJsselmeer. Year Water depth (m*) Increase IJm-depsit** (m) Net sedimentatin rate** (cm/a) Actual a depth cre (m) b * m:metersbelw mean sea level ** Theseclumns give theresultfcmparing theactual waterdepth, e.g. increaseijm-depsit f thenextrw with thisrw a Actual depthcre withut cnslidatin b Indicatin actual depth crewith rugh assumptin f cnslidatin factr (see als Chapter6) 52

40 DISTRIBUTION AND GEOCHRONOLOGY OFPRIORITY POLLUTANTS IN A LARGESEDIMENTATIONAREA f the barrier dam in 1932.Afterward, rapid sedimentatin f the IJm-depsit ccurred in this deep zne (Ente, 1981). Allpririty pllutants havebeen nrmalized and cntents seem t change radically during the last 60 a. This phenmenn is als evident fr the ther analysed cmpunds. In the cre, cncentratins f heavy metals, As and PCBs increase in depth t a maximum and then decrease t lwerlevels r backgrund. Water depths atthis gully during theperid give a gd impressin fthenet sedimentatin rate and give arugh indicatin f atime scale (Table 3.3). Changes in dry matter cntent with depth indicate cnslidatin f the IJm-depsit. The actual thickness f the IJm-depsit was 3.2 m. This ttallayerhas beendevided vertheyears ( ) based nfrmer water depths, dry matter cntents, net sedimentatin rateandcnslidatin. Cmbining thismethd with 137 Cs- (Cmans et al., 1989) and/r 210 Pb-dating (Eakins and Mrrisn, 1978)culd imprve the accuracy f the results. Beurskens et al. (1993) presented thegechrnlgy f pririty pllutants,based neightcresin LakeKetelmeer and wereablet derivecnsistent cncentratin prfiles (based n sedimentdatingin the IJm-depsit f this lake). One f these cres is presented with a crrespnding time axis (n the right)in Fig. 3.4 fr the Pb cntents during the last 50 a. The left axis f the figure shws the depth intervals and the derived time scale fr the cre f the IJm-depsit in Lake Usselmeer. The tw nrmalized Pbcncentratin prfiles have asimilar shape. Furthermre,if theleft axis isused tinterpret recent Pb cntentsandcntentsat 1978 inthe IJm-depsit flakeusselmeer,thesevalues crrespnd with the average Pb cntents aspresented befre. Als,the mean Pb cntent f the surficial sediment in LakeKetelmeer at 1978 crrespnds withthepbcncentratin prfile flakeketelmeer (Fig.3.4). depth (in cm.) n time (year ?"S ^ 1975! Lake Ketelmeer fMWl 1975 Lake Usselrr eer V) ys j 1940 f"! ;! nnn () 100 r _i J I 400 Leac nt H 500 ent ( n ng/kg 6( )0 dm ) Fig.3.4. Nrmalized Pb cntents in deeper znes (based n tw cres) f the IJsselmeer-depsit in Lake Usselmeer and Lake Ketelmeer frm 1932t

41 CHAPTER 3 Using the nrmalized values frm Vink and Winkels (1991) fr all ther pririty pllutants, similar cncentratin prfiles can bederived. The decreasefcntentsfpriritypllutantsin the IJm-depsit,gingfrm LakeKetelmeert the deeper znes in LakeIJsselmeer, can be characterized as adiluting factr. Bth therecent increasef carbnates in Lake IJsselmeer and a change f clay fractin cntent in time seem t be respnsible. Winnwing, ersin, resuspensin and transprt f ther fine sediment (clay fractin) in the entire LakeIJsselmeer,prirt the reclamatin wrks (befre 1975),seem respnsiblefrthe fine,lder IJmdepsit in the deeper znes f thepresent Lake IJsselmeer. This fine sediment and ther erded sediment is thught t be mixed and transprted tgether with the fine particulate lad f the river IJssel and depsited in the deeper znes f Lake IJsselmeer. Apart frm authigenic carbnate precipitatin, chemicalprcesses areassumed t belessimprtantfrthedilutinf pllutin thanthe physical prcesses mentined previusly. It is remarkable that fr each cntaminant a different diluting factr is fund. 54

42 Chapter 4 Gechrnlgyfpriritypllutantsin sedimentatinznesfthevlgaanddanubedelta incmparisnwiththerhinedelta HJ. Winkels,S.B. Krnenberg,M.Y. Lychagin, G. Marin, G.V.Rusakv and N.S.Kasimv based n: Winkels, HJ., S.B. Krnenberg,M.Y.Lychagin, G. Marin,G.V.Rusakv and N.S. Kasimv Gechrnlgy fpririty pllutants insedimentatin znes f the Vlgaand Danube delta,incmparisn withtherhine delta. Submitted t Appl. Gechem. 55

43 CHAPTER 4 Activity ( in Bq/kg) Vlga 150 Activity ( in Bq/kg) 8, Danube 100 l + \ XI \ 50 n i V A \ ^*^N., ( Organic Carbn (%) Organic Carbn (%) c Vlga Danube , + ++,,!' *,r^*t** 0! A A * x * x A Year f depsitin i Cre A Cre B À Cre C x Cre D + Cre E x Cre F Year f depsitin i Cre a Cre b A Cre c x Cre d + Cre e x Cre f Fig Cesium activities (A, B)and rganic carbn cntents (C, D) in sediment cre samples frm the Vlga (cres A, B,C, D, E and F) and Danube delta (cres a, b,c, d, eandf) vs. theestimated years f depsitin. Average activities and cntents in sediment cre samples are indicated by visually fitted curves. high sedimentatin rates than lcatins with lw sedimentatin rates (Eisenreich et al, 1989). In Figure 4.2A and 4.2B, Cs activities are pltted against estimated year f depsitin fr bth deltas. A certain amuntfvariatininactivitiescan bebserved,especially inthe 137 Csactivity fthe near surface samples in the Danube delta. Nevertheless, a clear pattern in Cs activities during the last five decades canbe distinguished and isindicated by visually fitted curves. Organic Carbn The rganic carbn (OC) cntent f suspended slids and sediment plays an essential rle in the behavir and fate f pllutants in the aquatic envirnment (Capel and Eisenreich, 1990). Mineraliza- 64

44 GEOCHRONOLOGYOFPRIORITY POLLUTANTS INSEDIMENTATION ZONESOFTHE VOLGA AND DANUBEDELTA tin prcesses affect the rganic matter in sediments. Based n the climatic differences between bth deltas, the impact f mineralizatin (related t higher temperatures and higher bilgical activity) in thevlgadelta is thught tbe higherthan inthedanube delta.if a cnstant input fochas ccurred inthepast, a decreasing OCcntent may beexpected atincreasing depthinthe sediment. In thevlga delta (Fig.4.2.C) a cnstant lw rganic input by the rivercan be bserved and these mineralizatin prcesses prbably ccured here. Hwever, in the Danube delta the OC cntent in the layers f the sediment cres werehigher and varied widely (Fig. 4.2.D). Surprisingly, therecently depsited layers have the lwestoc cntent. The highestlevels arefund inthe deepest layersinthe Danube delta. This can be explained by the fact that these yung clayey depsits are fund n tp f detritus and peat. Lcal rganic material in these lakes is prbably mixed with the clayey material during depsitin in thepast. The steady decrease inthe OCcntent inthe Danube deltais alspartly related t a decrease f the ttal OC lad in the Danube river upstream (Gherghisan and Osterberg, 1995). This decline prbably results frm the cnstructin f wastewater treatment plants in the drainage basin f the Danube sincethe 1960s. Heavy metals The cncentratin prfiles f three heavymetals (abslutevalues)fall cresareshwnfrbthdeltas infigure 4.3. Althugh nly three metals areshwn in Figure 4.3, similar cncentratin prfiles have beenmadefr all thermetals (Winkels et al, 1995;1996). Nevertheless,all metal resultsarediscussed belw fr bth deltas. Under the anxic cnditins prevailingin thesedimentsfdeltas, heavymetalsare relativelyimmbile and therefre, heavy metal prfiles are likely t reflect the histric inputs withut serius alteratins (Beurskens et al.,1993). Surprisingly lw, cnstant cncentratins f arsenic, chrmium, cpper and zinc are fund during thelast five decades in thesedimentsfthevlga delta. Thelwestcncentratins ftheheavy metals Ni, Zn, Cu and Cr were bserved in the early 1940 in this delta. Recently depsited sediments in the Vlga delta seem t shw slightly increasing levels fr the metals zinc and arsenic. These lw metal cncentratins in the sediment cres in the Vlgadelta are in agreement with cncentratins fund in the sediments sampled evenly spread vertheentiredelta (Lychagin et al.,1995). Theheavy metalsin the sediments f thevlgadelta seem thave natural backgrund values. The heavy metal prfiles in the Danube delta all have a typical pattern. The recent decrease f all heavymetalinputsint the river Danube since 1987 indicate the recent failure f industrial prductin due t pliticalchangesineasterneurpe. Theheavy metals zinc,mercury andcpperhaveincreasing cntents till 1987, prbably crrespnding with increasing industrializatin in central and eastern Eurpeinthe peridbefre Thehighest nickel cntent isfund inthe perid arund After thisperid the nickel cntents are slwly decreasing. Therecently depsited sediments inthe Danube delta have the lwest arsenic, nickel, lead and chrmium cntents ever bserved during the last five decades. The heavy metal cntents, except cadmium and chrmium, are in general higher in the Danube deltathan inthevlga deltaduring thelast five decades. Thedatafrm thenndegradable,relatively immbile metalsindicatethat resuspensin and biturbatin havehad nly limited effects n thepllutant prfiles. Cnsequently, cmbinatin f data frm all dated cres int ne graph appeared t be a feasible and elegant methd t interpret the results. Hwever, therprcesses,suchasdiffusin andtransprt withinfiltrating water,may haveaffected the cncentratin prfiles f smerganicpllutants (Beurskens et al, 1993). T illustrate thatvisually fitted curvesdnt changedue tchangingclayfractin andrganicmattercntents,figure4.4 has been drawn.in this figure nrmalized chrmiumcntentshave been drawn 65

45 CHAPTER 4 Cr-cntent (mg/kg) Cr-cntent (mg/kg) S Danube w 50 / *«x Y LL i... i Cu-cntent (mg/kg) Cu-cntent (mg/kg) Danube Zn-cntent (mg/kg) Zn-cntent (mg/kg) Danube l/j. * * A * * Year f depsitin Cre A Cre B A Cre C x Cre D + Cre E x Cre F Year f depsitin i Cre a Cre b A Cre c x Cre d + Cre e x Cre f Fig Cncentratins f chrmium (A, B), cpper (C, D) and zinc (E,F) in sediment cre samplesfrm the Vlga (cresa, B, C, D, Eand F)and Danubedelta (cresa, b, c,d, eandf) vs. theestimated yearsfdepsitin. Average cntents in sediment cre samples areindicated by visually fittedcurves. 66

46 GEOCHRONOLOCY OF PRIORITY POLLUTANTS IN SEDIMENTATION ZONES OF THE VOLGA AND DANUBE DELTA 150 Nrmalized Cr-cntent (mg/kg) Vlga 150 Nrmalized Cr-cntent (mg/kg) S Danube 'j^r 50 it * + I$P Year f depsitin 0 I I > i.. i Year f depsitin Cre A Cre B, Cre C Cre a Cre b A Cre c x Cre D + Cre E Cre F : Cre d + Cre e x Cre f" Fig Nrmalized cncentratinsfchrmium (A,B)in sediment samplesfrm thevlga (Cres A, B, C, D, E andf) and Danube delta (cres a, b, c,d, eandf) vs.theestimated yearsf depsitin. Averagecntents in sediment cre samples isindicated by avisually fitted curve. fr allcresin bth deltas. The nrmalizedchrmium cntentshave thesame histricpllutin pattern by the Vlga and Danube river as that in Figure 4.3A and B. Because the differences in physical characteristics between the cres in the sediments f the Vlga delta are higher than in the Danube delta, thedifferences between absluteandnrmalized cntents arealshigher here. Nevertheless, the nrmalized results dntdiffer in away that theresults f this study are substantially affected. PCBsandPAHs The cncentratins f seven investigated PCB-cngeners in the sediments f the Vlga and Danube delta werefr all samples in every crebelw detectin limit (<0.005 mg/kg). The absence f rlw prductinratesf PCBsin middleandeasterneurpean cuntries, might be respnsible.furthermre micrbial dechlratin prcesses in the anxic sediment in these deltas might have had influence, as has been shwn in ther anxic sediments in the field and in the labratry (Brwn et al., 1987a,b; Quensen et ai, 1988, 1990; Beurskens et ai, 1993). Ten different PAHs were determined in all layers f the twelve cres frm bth deltas. Recently, McFarland and Sims (1991) presented a thermdynamic evaluatin f the bidegradability f PAHs under anaerbic cnditins. They indicated that micrbially mediated transfrmatin f PAHs in anaerbic envirnments may ccur under denitrificatin cnditins, but is unlikely t ccur under sulfate-reducing andmethangenic cnditins.inlabratry experiments, micrbialtransfrmatin f the bicyclic naphthalene and acenaphthene hasbeen shwn under denitrificatin cnditins (Mihelcic andluthy, 1988). Because methangenic cnditins prevailin sediment frm bth deltas, pstdepsitinal bidégradatin f PAHs can be excluded. Cnsequently the cncentratin prfiles f PAHs in bthdeltaswillpresumably reflect theunchanged histricinputs. Thesedimentsf thevlga deltaare ntcntaminated withpahsandhavelwnatural backgrund values. In Figure 4.5 the cncentratin prfile is shwn fr the sum f ten individual PAHs in the 67

47 CHAPTER 4 Sum lopahs (mg/kg) Danube Year f depsitin Cre a Cre b A Cre c x Cre d + Cre e x Cre f Fig Cncentratins f sum 10PAHsin sediment cre samples frm the Danube delta (cres a, b, c,d, eandf) vs. the estimated years f depsitin. The averagecntent in sediment cre samples is indicated by avisually fitted curve. Danube delta.inthis figure there is aslw increase inthepah cntents during theperid The recent decrease f all PAH cntents in the sediment f the Danube delta crrespnds with the decrease f PAH inputs int theriver since 1987, presumably reflecting therecent failure f industrial prductin due tplitical changes in eastern Eurpe. The higher PAHlevels in the deepest layers in the Danube delta might be due t higher natural backgrund levels in the underlying peaty layers. Lcal rganicmaterial withhighernaturalpahlevelsintheselakesis prbably mixedwith theclayey material during depsitin in thepast. B. Cmparisn withthe Rhine delta Radicesium activities and rganic carbn If ne cmpares theradicesium curves with thse frm the Rhine delta (Chapter 2), the 137 Cs maximum f the early 1960s has similar activities in all deltas. The fallut frm the nuclear pwer plant accident in Chernbyl is respnsible fr n measurable activities in the Vlga delta and twice higher activities inthe Danube deltathan intherhine delta.this can be explained based ntheir gegraphicallcatin and the mainly suth-western winds during and after the accident. Therganicmatter cntentsinthe aquatic sedimentsf thevlgaand Danubedeltaarerespectively threetimes and twiceaslwas thseintherhinedelta (Chapter 2).Theimpact fmineralizatin prcesses, due t climatic differences, and the carbn input int the rivers during the years can explain mst differences inrganic carbn inthehistric carbn prfiles f the three deltas. Pririty pllutants Asan example,in Figure4.6theabslutecntentsf arsenic,nickelandsum 6PAHsare presented fr all three river deltas during the last five decades. The visually fitted curves fr each cntaminant are given, based n thecncentratin prfiles derived inthis paper, by Winkels et al., 1995 and 1996and in Chapter 2. Thehighest arsenic cntents have been fund inthe deltaf the river Rhine. The lwest cntentsarefund inthedeltaf the rivervlga. The Danubedeltahasarseniccntentsin betweenthe 68

48 CEOCHRONOLOGY OF PRIORITY POLLUTANTS IN SEDIMENTATION ZONES OF THE VOLGA AND DANUBE DELTA 1000 Cntent (mg/kg) Arsenic Cntent (mg/kg) 100 Nickel 80' 60 I _ I_LX Cntent (mg/kg) Sum 6PAHs Year f depsitin Rhine Danube Vlga Fig Average cntents f arsenic (A), nickel (B) and sum 6 PAHs (C) in sediments frm the deltas f the rivers Rhine, Danube andvlgavstheestimated yearsf depsitin. 69

49 CHAPTER 4 Table 4.3. Average cntents f heavy metals, PAHs and PCBs in the sediments in the deltas f three majr Eurpean rivers during threetime perids (in mg/kg) Rhine delta Danube delta Vlgadelta Arsenic Cadmium Chrmium Cpper Mercury Lead Nickel Zinc X7PCBs' SóPAHs < < < < < < < < < < < < < < < < PCB-cngeners (IUPAC n.): 28, 52, 101,118, 138, 153 and 180 PAHs:fluranthene, benz[k]fluranthene, benz[a]pyrene, benz[b]fluranthene, benz[ghi]perylene and Indenpyrene ther deltas during the last five decades. Fr the sum f six individual PAHs similar differences have been fund between the three deltas. Cntents f nickel are similar in all deltas during the last five decades.similar figures can bederivedfr alltherheavy metals, individualpahsand PCBs. InTable 4.3 the resultshavebeen summarized fr three specific years during the last five decades. The Rhine delta is the mst cntaminated delta, it has the highest levels f heavy metals (except nickel),pcbs and PAHsduring thelast five decades. The deltaf the river Danube has elevated cntentsfheavy metals andpahs,but islesscntaminated than therhine delta. The Vlga delta is nt cntaminated, it has mainly backgrund levels f heavy metals, PAHs and PCBs.If theactual (1990) heavy metal cntents nthe suspended slidsinall rivers arecmpared the cntents in the riverrhine are thehighest (except fr nickel) and lwer levels are fund in the rivers VlgaandDanube. The natural (backgrund) input, due t gelgic differences in each catchment area, and pllutin inputby industrial activity int therivers during theyears can explain mst differences in the histric cntaminant prfiles f the Danube and Rhine delta. Fr thevlga delta nly the first reasn (natural backgrund input) can explain the lw and cnstant histrical cntaminatin. The sediments in the Vlga deltareflect analmstnatural unplluted river system. Nevertheless industrializatin in the Russian Federatin has undubtfully resulted in cntaminatin f the Vlga river. Presumably the sediments f the Vlgadelta are nt cntaminated, because cntaminatin is trapped by the sediments in artificial strage lakes upstream f Vlggrad (Batyan and Zajtsev, 1985). Pssibly, the recently increasing levelsf zinc and arsenic in this delta are a first result f the nt permanent trapping f the cntaminatin in these strage lakes.if s,the stragef thesecntaminated sediments culd be cnsidered a chemical time bmb fr the delta in the near future (Gerasimva and Hekstra, 1994). Furthermre the natural meandering f the river Vlga in its large fldplain and high bilgical activity due t higher temperatures in this regin might have had a purifying effect n the cncentratins f cntaminants here. Basedn the average dischargein each river and their average cntentsfsuspendedslids, als the lad f pllutants can be calculated fr each delta. The results f these calculatins are presented in Table

50 GEOCHRONOLOGY OF PRIORITY POLLUTANTS INSEDIMENTATIONZONESOFTHEVOLGA AND DANUBEDELTA Table 4.4. Estimated heavy metal-, PAH- and PCB-lads depsited in the deltas f three majr Eurpean rivers during three perids (in tns a year). Rhinedelta Danubedelta Vlgadelta Arsenic Cadmium Chrmium Cpper Mercury Lead Nickel Zinc 27PCBS' E6PAHs PCB-cngeners (IUPAC n.): 28, 52, 101,118, 138, 153 and 180 PAHs:fluranthene, benz[k]fluranthene, benz[a]pyrene, benz[b]fluranthene, benz[ghi]perylene and Indenpyrene Arund 1940and 1990 the lad f mst pllutants (except Hg, Cd and PCBs) is the highest in the river Danube.Arund 1970 theladf all pllutants is the highest fr theriver Rhine. TheVlga river has the lwest lads during thelast five decades. Cnclusins - Sampling unifrmely sft anxic aquatic sediments in the Vlga and Danube delta, using Cs-istpe-dating and satellite images (with intensity f suspended slids) resulted int cncentratin prfiles f heavy metals and PAHs that reflect, withut serius alteratins, the histric pllutin input intthese rivers. - The cntentsf 7 investigatedpcbs (<0.005mg/kg)and cadmium (<0.5mg/kg) werebelw detectin limitfr all sediment samples in thevlgaand Danube delta. - Lw and hardly changing cncentratins f arsenic, cpper, zinc and all studied PAHs were bserved during thelast five decades intheaquatic sediments f the Vlga river. Nickel cncentratins in the aquatic sediments in the Vlga delta are rather high. Recently depsited sediments seemed t shw slightly increasinglevelsfr the heavy metalszinc, chrmium andarsenic. - The pllutin histry f thedanube ischaracterized as fllws: * Lw cncentratins f metals were bserved in the early 1940s. PAHs levels were already elevated. * Increasing levels f metals and PAHs were fund between 1950 and Arund 1987 the highest levels everbserved in this deltawere fund fr bth metals andpahs. * Recently depsited sediments had ratherlw cncentratins f metals andpahs. - If thecntents fheavy metals,pahsand PCBsinthe aquatic sediments inthe deltasf the rivers Rhine,DanubeandVlgaare cmpared, itis clearthat thevlgadelta isand wasthecleanest delta duringthe lastfive decades. Nwadays thecntents fheavy metals (exceptcpper and nickel),pahsand PCBs inthe aquatic sediments f the river Rhine are still highest cmpared tthe ther tw rivers. 71

51 CHAPTER 5 defined ashalf thec-variancebetween pair differences f thetw variables Z(x)and Y(x). Thecrssvarigram y zy (h) is estimated as half f the average prduct f /ï-increments relative t tw different attributes Zand Y (Deutsch andjurnel, 1992): 1 N Z y(h) 2N zy (h) i = \ where {z(x,), z(x i+h )} and {v(x,-), y(x i+h )} dente the rth pair f bservatins n Z(x) and Y(x), respectively, separated by distance h; and Njiji) isthe ttalnumbers f such pairs. Thevarigrams between current andfuture bservatin pintscan beused tcalculate the ptimal grid spacingfr sampling (OGS, necessary tmnitr eachvariablein a regular grid) tacheive a predetermined levelf accuracy (PA). ThePA, inthe same units as thevariables,isdefined as the highest uncertainty that exists n an interplated map.it isequal tthekriging standard deviatin in themst islatedlcatinfpredictin,i.e.the centre pintf a squaregrid cellwithbservatinsineachfthe crners f thiscell. Thekriging standard deviatin is Stdev. = ^g' 0 G- l g 0 -x a Vx a (3) where g 0 isthevectrwith varigram valuesbetween bservatin lcatin and thepredictin lcatin, G is the n x n matrix with varigram values amng the bservatin lcatin, 1 isthe vectr f n elements all equal t 1, x a = 1 - g' 0 G~' l n and V- (l' n G A 7 )~'.One may ntice that equatin (3) des nt depend upnthevectrf bservatins. Because it desdepend upnthevarigramandupnthe cnfiguratinf the data pints, it may be used t ptimize the cnfiguratin f the sampling scheme as fllws. Given thevarigram, themaximum ccurringuncertainty fr e.g. asquaregrid withmesh bis determined. If this uncertainty is belw the specific level b 0, b is dubled, therwise b is halved until the value b 0 is reached. Inthisstudy,theiterativecmputerprgram OPTIMwasusedtcalculatethe ptimal grid spacing (OGS),based npredetermined accuracies (PA)feach variablein a triangular and squaregrid. Starting with the largest spacing, grid spacing is reduced untilpais reached. Minimizing predictin errrs is nly useful if the riginal data set is nt severely clustered (Isaaks and Srivastava, 1989). In this study, the ptimalspacingfr a square gridwas calculatedfrtheselectedvariables (CF, OM, Cu, BAP and TC) using their specific varigrams with fitted mdels. OPTIM was nt used fr the variables which havedeclustered means thatdiffer mrethan 15% frm their rdinary meanvalues. Predetermined accuracy can be based n gvernmental regulatins, but ther practical values can be chsen as well.weptimized grid spacing with the (individual) standard deviatin f the variable ineachgrupaspa l5 yielding OGS^ Varigramswith a nugget valuehave a minimum predetermined accuracy (MPA). A PA lwer than the square rt f the nugget value fr these variables cannt be achieved. Frmnitring purpses, itisinteresting tcmpare ptimal grid sizesf the same variable between the sample dmains. Fr example, we chse apa 2 just abve the highest MPA f each variable and calculated OGS 2. Resultsanddiscussin Summary statistics and crrelatins Summary statisticsfr 10 parametersfallsamples (n = 138),and separatelyfr sub-areasg] (n =55), G 2 (n =53) and G 3 (n - 40) aregiven intable 5.1. Standard deviatins arerather highfr all samples, 80

52 OPTIMAL COST-EFFECTIVE SAMPLING FOR MONITORING AND DREDGING OF CONTAMINATED SEDIMENTS O Ü 1 g c il s 2 2 CO CM CS in Ö O ON S in O CS in ni ^f O O s in NO es es es NO CN q NO c NO ** CM ^_, CO NO ON CN CJO ON es r- c Os c Zn* es es NO in Os es es in O in 00 NO O O CO O CO Ö CO d CO NO es «n es NO 00 Os O 00 ^1-00 CO es CO in in 00 NO O 00 VC CO CO es r--^ m <S a e e «3 O I e s 2 CO u 2 in ON»n Vi es c ~~i O Os in c in in ~ i n ^ - O O O O O O Ö Ö Ö Ö Ö Ö Ö Ö O r- - H O O O O O O O N O (N m in ^ (N T) NO in es Tf 1 1 NO NO ^t r~- in ^i t-- O S " c ON O (S) t> in ^ ^ s 3 rt es ' (N 00 iti CN ^ q ^ f p p p p p p r ^ i n c N Ö Ö Ö Ö Ö Ö es es es Cd «; ^t- <*- Ö 3 O. rù ca >< ca a S a- <L» tu Q CO c n < N ^ O O O O O O O N ( N ^H Tfr V,. - r-~ in Ö Ö Ö Ö Ö Ö T - t ^ es n \ N in m \ô \d U xi ea us 2 Q OO ON iri ^ O ^; ^ 0Ô -^ Ö vi ^ Ö Ö -H in <n m r- r- ^ ö < ^ Ö Ö Ö Ö O Ö r- in ON en m ^ D f N Ö Ö Ö Ö Ö Ö ON O O»n en' O z eu O I *0 ON in ON en O ö ^ ö ö ö c~ in t^ g) ) 1^ tf tj)"^"^ c aa m â E S E u u te,' tu M 2 u U- Ä X= N C XI 2 C 2 u c 2 81

53 CHAPTER 5 duetlargedifferences indegreefcntaminatin between G 2 and thether sub-areas. G 2 cntainsall the sandy samples,in the eastern part f Lake Ketelmeer, with lessclay and rganic matter, and lwer cntaminant levels. Lw levels (clse t detectin limits) f plycyclic armatic hydrcarbns and rganic matter within G 2 are mainly respnsible fr the rather high standard deviatins fr thse variables. Psitively skewed distributins are fund fr the same parameters at G 2, again with high standard deviatins. Except fr TC,samples f G { and G 3 have cmparable variables accrding ttheir averagevalues, distributins and standard deviatins. Average cntents give a gd indicatin f the degree f cntaminatin in the tp layer f Lake Ketelmeer. These values crrespnd t and underline the recent imprvement f water and sediment quality reprted in ther studies (Winkels et al., 1990;Beurskens et ai, 1993; Beurskens étal., 1994). A Mest shws that all values f parameters and cntaminants are significantly lwer in G 2 than in G! r G 3. Basednthesummary statistics,allpredefined grupschsenwiththissampling strategyare significantly different frm each therfr atleast ne variable. Declustering weights arelessthan 1 fr thesamplepintsinthecrsses,leading tlw declustered means fr the selected variables inall grups (Table5.1).Thechsen sampling schemewith crssesis therefre respnsible fr declustered means 11.5% lwerthan calculated meansfr each variable. The declusteredmeansf especiallythe clayfractin cntent and the cpper cntent in sub-area G 2 are very lw,prbably because the crss is incidentically lcated in a regin f lw clay cntent. Crrelatins between parameters (Table 5.2) are in general high (ne tailed significance = 0.001) fr all variables and cntaminants, excepting Cd, which nly relates t OM and Cu. All ther cmpunds crrelate significantly with each ther and with rganic matter. Significant crrelatins have been fund between rganic matter and metals in this lake (Ente, 1981).Winkels et al. (1990) prved that plychlrinated biphenylsare als relatedt the rganic mattercntentin sediments. Inthe present study, crrelatins are als significant between the PAHs and rganic matter and between each f the PAH variables.theserelatins indicate thattheinvestigated PAHs riginate mainly frm atmspheric depsitn, related t the cmbustin f fssil fuels (Beurskens et al., 1993). These crrelatins als supprt the chice f BAPas a selected variable. Table 5.2. Crrelatin cefficients f sediment characteristics and cntaminants in Lake Ketelmeer (all 138 samples). One tailed significance: * = CF' OM 1 BBF 1 BKF' BGP' IND' FLU 1 BAP 1 Cu' Cd 1 CF 1.00 OM BBF BKF BGP IND FLU BAP Cu Cd 0.88* * * 0.92* * 0.84* 0.82* * 0.96* 0.90* 0.81* * 0.98* 0.93* 0.79* 0.95* * 0.82* 0.81* 0.87* 0.78* 0.78* * 0.93* 0.70* 0.67* 0.63* 0.65* 0.66* 0.63* * * CF,OM,BBF, BKF,BGP, IND, FLU,BAP, Cu,Cd areclay fractin, rganic matter, benz(b)fluranthene, benz(k)fluranthene, benz(ghi)perylene, idenpyrene, fluranthene, benz(a)pyrene, cpper and cadmium cntents, respectively. 82

54 OPTIMALCOST-EFFECTIVESAMPLINGFOR MONITORING AND DREDGINGOFCONTAMINATEDSEDIMENTS Table 5.3. Estimated parameters f spherical r linear varigram mdels fr selected variables in tp layer sediments f three grups inlake Ketelmeer. Grup Variables 1 mdel type 2 nugget sill range (m) rss 3 R 23 G, TC (cm) CF (%) OM (%) BAP(mg/kg) Cu (mg/kg) S S L S S G 2 CF OM BAP Cu S S S S G, TC CF OM BAP Cu S L L S s TC,CF, OM,BAP,Cu arethickness fcntaminated layer, clay fractin, rganicmatter, benz(a)pyrene and cpper cntents, respectively. Spherical mdel (S)defined as: y(h) = N 0 + c( 3h/2a - l/2(h/af ) frh<a y(h) = c fr h>a Linear mdel (L)defined as: y(h) = N 0 + bh frh>0 where N, aand crepresent thenugget, therangeand the sill value, respectively. rss = theresidual sum f squaresfr spherical mdels; R 2 =squared crrelatin cefficient fr linearmdels. Spatial variability Estimated varigram parameters aregiven in Table 5.3.Varigrams were calculated using 8, 10r 15 lags, with lag length varying frm 185 m t 350 m.varigrams f CF and OM are shwn in Fig. 5.3; varigrams f Cu and BAP in Fig. 5.4; and varigrams f TC in Fig Sme distance classes cntainlessthan30 pairsf pints, but theyaregivenas well. Thsevarigram valuesare likelyt beverestimated, sthey were given less attentin when fitting the mdels.in general, the spatial variability f theinvestigated variables in the sediments fthislakecan be succesfully described by varigrams. Three ut f six varigrams f the sediment characteristics d nt reach a sill value, yielding a linear mdel. The sill value fr CF is reached at a shrter range in G!than in G 2,whereas the range almst dubles in G 2 cmpared t G,. Frbth cntaminants, spherical mdels were fitted,the gdness-ffit expressed intable5.3by theresidual sumf squares (rss). Alwrssvalueindicates anadequate fit f the spherical mdels.frthe linear mdels,the gdness-f-fit is indicated by the squared crrelatincefficient (R 2 ). Themeasurement errrsexpressed asnugget valuesfr Cu and BAP are clse t zer. The sillvaluefrthese cntaminantsis reacheding[at a larger rangethaninthethersub-areas, whereas the rssvalue indicates a less adequate fit. The nugget valuesfrtcare ratherhighin bth sub- 83

55 CHAPTER 5 5 Varigram (% 2 ) Qf Varigram (% 2 ) " - Of ^ ^ s^ 93 V 86 87,35 S S^~ SÏ1Ï2 iey* '' + ^274 j 2 7 OM CF 7*106, / ~ -, """ /, ' 220^<r^ 169 ' j>^302 CF OM i i i ? <V [ r ~39^ i 115 i + 96 ) Distance (km) 36 i 23 i CF i i i i OM i i i Distance (km) Fig Varigrams fclay fractin (CF) and rganicmatter (OM)fr sub-areas G G 2 and G 3. 84

56 OPTIMAL COST-EFFECTIVESAMPLING FOR MONITORING AND DREDGINGOFCONTAMINATED SEDIMENTS Varigram (10 3 mg 2 /kg 2 ) Varigram (mg 2 /kg 2 ) 102 / / 4 jt 3 / "-S3 F/2741^7 /l47 / Cu G, r / ' Cu /" 1 f^ js + S 56 6 t i BAP r - G Cu Distance (km) - - ^144 iys $ BAP % Distance (km) Fig Varigrams fcpper (Cu) and benz(a)pyrene (BAP)fr sub-areas G G 2 and G 3. 85

57 CHAPTER 5 Varigram (m 2 ) Varigram (m 2 ) <67 G f 144 'J?/ iiy "7 8/ 77 JH^I^ 861U 135 TC a 32 i i i Distance (km) + 39 TC Distance (km) Fig Varigramsf thickness cntaminated layer (TC)fr sub-areas G, and G 3. areas. Sill valuesfr TCare reachedatdifferent rangesin bthsub-areas,shwing a high shrt-distance variability in G,. Crrelatins existbetween cntaminants andrganicmatter,and between thecpperandclay fractin cntents. T investigate the spatial dependence between these variables, crss-varigrams were cnstructed (Figs. 5.6, 5.7, 5.8). If spatial c-dependency was fund, crrelatin cefficients (r 2 ) are given in the upper-left crner f the figures. CF-Cu and CF-BAP are spatially c-dependent parametersing 3, whereasom-cu and OM-BAParespatially c-dependent in G, and G 3. Spatialvariatinin cntaminants therefre prbably relates t spatial variatin in rganic matter cntent. Further, TC is spatially c-dependent withomand CFin G^ In G 2, spatialvariatinfcntaminatin desntrelate t sediment characteristics. Sampling strategy fr mnitring and dredging Analysis f spatial variability thrugh the design f an adequate sampling grid culd be helpful when mnitring similar ecsystems inthefuture. Frthedredging f 20 km 2 in Lake Ketelmeer (t beexecuted befre 2000), a gridpatternfr adequatemeasurement f the thicknessf the cntaminated layer hastbechsen.we usedoptimtdeterminethegrid spacing necessary tachieve a predetermined levelf accuracy. OPTIM was nly used n variables in grups with declustered mean values similar (less than 15% difference) t rdinary mean values. In Fig. 5.9, the required grid spacing fr three variables isgiven as afunctin f precisin btained inlake Ketelmeer. Inthe central part f the lake (G^, wenticethat agrid spacingf 607 m yieldsinterplated TC mapswith a maximum uncertainty f 12 cm. Fr G 3 the same accuracy was reached with a grid spacing f 33 m. This means that in harbrs and near the shres f the lake r shipping rutes,the thickness f thecntaminated layer has t be surveyed with a grid spacing that is 18 times as dense. The minimum predetermined accuracy pssible fr TC is a very imprtant factr fr dredging. If the thickness f the layer in G 3 cannt be estimated with an accuracy greater than 12 cm, then it is nt necessary t dredge it mre accurately either.this desnt mean,hwever,thatdredging equipmentdesntneed t bevery accurate.accuracy f bth equipment and mnitring needs t be taken int accunt when remving cntaminants. Therefre, when remving cntaminated layers dredging shuld be dne t an verdepth f at least 86

58 OPTIMAL COST-EFFECTIVE SAMPLING FOR MONITORING AND DREDGING OF CONTAMINATED SEDIMENTS 150\ Crss-varigram Crss-varigram 1 G I + 2 Î * PO'J 273 ' 141 " CF-Cu -1 1 i i CF-BAP! G ' ~7A ~+ + + 'i i CF-Cu i i CF-BAP 150 = i 2 = ^ JK'' 19 'f*--'" ^^ "46 13b _j CF-Cu i_ 3 4 Distance (km) i CF-BAP 3 4 Distance (km) Fig Crss-varigramsfclay fractin (CF) withcpper (Cu)andwith benz(a)pyrene (BAP)fr sub-areas G,, G 2 and G 3. 87

59 CHAPTER Crss-varigram =0.9* 6» r Crss-varigram l^sftst G, *44 «X""' /< 179^ ^ ^ 141 /179»« s^203 64*'$/+ OM-Cu ^ ^ ^ SO ^ ^ ^ OM-BAP i r - G _ i « OM-Cu > i t 00 I OM-SAP r. r^o Distance (km) 3 4 Distance (km) Fig Crss-varigrams f rganic matter (OM) with cpper (Cu) and with benz(a)pyrene (BAP) fr sub-areas G 1; G 2 and G v

60 OPTIMAL COST-EFFECTIVE SAMPLING FOR MONITORING AND DREDGINGOFCONTAMINATEDSEDIMENTS Crss-varigram 100. i Gj 50 Crss-varigram?=0.91 ' 50 0 : ^ J -r-~. Aa J&4 Z " S 212 '*' ^*-^ m i CF-TC i -50 OM-TC 100 % If y a2-124 ' i I CF-TC 3 4 Distance (km) i -50 OM-TC 3 4 Distance (km) Fig Crss- varigramsfclayfractin (CF)andrganicmatter (OM)withthickness cntaminated layer (TC)fr sub-areas G, and G 3. 7 cmin G,, andpreferably 12cmin sub-area G 3, tmake sureall cntaminatin isremved. Remval cstwill f curse be higher. Table 5.4 gives tw predefined accuracies (PA^ PA 2 ) with crrespnding ptimal grid spacings (OGS,, OGS 2 )fr the variables in each grup.pa!is the standard deviatin f each variable intable 5.1. Fr mnitring purpses, we chse as an example a PA 2 just abve the highest MPA f each variable, yielding OGS 2 In Table 5.4 the minimum predetermined accuracy (MPA) is given between bracketsfreachvariablein each grup. Table5.4is depictedby Fig.5.9,whichshws the ptimalgrid meshfr Cu,BAPandTCfrtw r three sub-areas.t btaininterplated Cu mapswith a maximum uncertainty f 14 mg/kg, samplespacing shuldbe 1150 ming[ and 450 ming 3.T btain Cu maps with amaximum uncertainty equal t the standard deviatin f the variable within the grup, spacing shuld be2000 min G, and 818 min G 3. FrBAP, samplespacing must be 270 min G 1023 min G 2 and 968 ming 3, t reach apredefined accuracy f0.25 mg/kg. Thisprvesthenecessity tdivide the aquatic ecsystem int sub-areas t reliably sample its sediment. Fr sensitivity analysis, the OPTIM prgram was tested fr the BAPcntents in G 1( where fr the 89

61 CHAPTER 5 Table 5.4. Required sample spacing fr mnitring f variables, based n predefined accuracies, in grups f tp layers f sediments inlake Ketelmeer. Grup Variables 1 Mean PA, 2 OGS, 2 PA 2 2 OGS 2 3 [MPA 4 ] G, TC CF OM BAP Cu [6.5] [-] [-] [0.20] H G 2 OM BAP [0.47] [0.01] G 3 TC CF OM BAP Cu [11.1] [1.95] [0.61] H [12.7] TC,CF,OM,BAP,Cu arethickness f cntaminated layer, clay fractin, rganic matter, benz(a)pyrene and cpper cntents,respectively. Predetermined Accuracy (incm, %rmg/kg) with PA, as the standard deviatin ftheparameter within itsgrup and with PA 2 asan example tcmpare the sub-areasfr each variable. Optimal regular Grid Spacing fr mnitring (in m)with OGS, based npa, and OGS 2 based npa 2. Minimum Predetermined Accuracy (in cm, % r mg/kg). Table5.5. Sensitivity f OPTIM fr three different nugget effects (N 0 )n the sample spacing f benz(a)pyrene (BAP) in G, with thefitted spherical varigram (Table 5.3), based n apredefined accuracy f OGS' (m) Precisin btained (mg/kg) N 0 = /V =0.18 JV = Optimal regular Grid Spacing (OGS) in meters 90

62 OPTIMAL COST-EFFECTIVESAMPLING FOR MONITORING AND DREDGINGOFCONTAMINATEDSEDIMENTS Precisin btained (mg/kg) Precisinbtained (mg/kg) a» 0.30 <P Required grid spacing (m) 0 i» i i i» i BAP Required grid spacing (m) Precisin btained (cm) TC Required grid spacing (m) Fig Sample spacing required t measure thickness f cntaminated layer (TC),cpper (Cu) and benz(a)pyrene cntent (BAP)in sub-areas G,, G 2 (nly BAP) and G 3,as afunctin f therequired accuracy. spherical varigram mdel N 0 is settequal thefitted value (0.037),the sill (0.18)and 0,respectively (Table 5.5). OPTIM is nt sensitive, i.e. the uncertainty is high and des nt change if the spherical mdel changes int a pure nugget effect. If N 0 = 0, hwever, precisin is reduced by factrs 0.3 and 0.55 fr the sample spacings f 500 m and 125 m, respectively; OPTIM is therefre sensitive t the presencef anugget effect. T mnitr ne cntaminant in the entire lake theresults fr each sub-area given abve areused t selectanptimalsamplingpatternfr thefuture. Asan example, thebap resultsin thislakehave been used.tidentify the ptimal sampling patternfrfuture BAP mnitringin the entire lake, thefirst and mst lgical slutin is tchse the densest netwrk, giving the highest accuracies fr all sub-areas. This wuld result in t many sampling pints in at least tw sub-areas, s it wuld be unnecessarily expensive.further, itisdubtful whether thepredefined sub-areas are representativefthe nn-visited areas. Thesecndptinis tsampleeach sub-area basedn the calculated accuraciesfrbap, which isstatistically a gdchicebut causes a prblemwhendecidingupn a patternutside these areasand fr G I+3, theverlapping areaf G\ andg 3. Fr thse areas,ne culdchse asampling distancethat 91

63 CHAPTER 5 isthe average distance f thepredefined sub-areas.anther pssibility istrecalculate theentire area byenlarging sub-areaswiththezneswhichare lcatedclsest. Thiswuldresultint a denserpattern (with higher csts)frtheenlarged sub-areas tachieve thesamepredefined accuracy. The thirdptin is t sample nn-visited areas als and t calculate the minimum necessary grid spacing fr BAP in theseregins. FrmthedatainTable5.4,itisdifficult tchsethe ptimal sampling grid fr future cntaminant mnitringinthis lake.frexample,neculd selectthecalculated grid spacingf Cu rbapin G 1; but then the chice f the predefined accuracy fr each cntaminant wuld be different. Wesuggest a chiceusing thefllwing practical cst-effective methdlgy: 1. If the budget is sufficient, then the densest grid spacing shuld apply t all variables; nn-visited areas shuldbe sampled with a similar densepattern.if thebudget islimited, use Rules 2and If high crrelatins between variables arefund (R 2 >0.8), andthey are spatially c-dependent (r 2 >0.8),then thelargest samplespacingf the tw variablesbasednsimilarpa valuescanbe used. Because cntaminants are mre expensive t analyse than sediment characteristics, it is als pssible t substitute a cntaminant with a cheaper variable (t analyse).optimum cst-effectiveness can be btained by substituting the largest sample spacing fr the densest ne, and t replace the cntaminant with the sediment characteristic cheapest t analyse. If n gd crrelatins and c-dependencies are fund, then the densest, and mre expensive, sample spacing must be chsen. 3. If threshld values f cntaminants n which mnitring needs t be based are, accrding t gvernmental regulatins, exceeded in a sub-area, then the sample spacing f this cntaminant is used tmnitr this sub-area, ruseitssubstitutebasednrule 1. If nt,usethedensest gridsize. Weused this methdlgy fr G u wherehigh crrelatins and c-dependence exist between OMand Cu. Assuming the highest PA f BAP (a 33% difference frm the mean) and nn-excedance f threshld values (based ndutch gvernmental regulatins) fr each cntaminant in Lake Ketelmeer, thegrid sizefr mnitringcntaminantswuld be270m. Fr thisgridsize, BAP needs t beanalysed at every sampling pint and OM has t be sampled in a grid size f apprximately 2700 m. Fr practical reasns related t the ttal size f the area, OM can be measured at every hundredth BAP sample pint. Based n the relatin between OM and Cu, cpper cntents can als derived fr this sub-areafrm measurements f OM. If this gestatistical apprach had nt been used fr cntaminant mnitring and t calculate the thickness f the cntaminated layer inlake Ketelmeer, accuracies wuld havebeen lwer and survey cstswuld have beenhigher.in general,in the Netherlandsandther cuntries,grid patternsare based upn thelimitedfinancial budgetsavailablefr aquatic mnitring.previusly, budgetsfrthe remval f cntaminated sediments in ther Dutch harburs have been exceeded because mnitring failed t prduce accurate maps fr dredging (Rijkswaterstaat, Pers. cmm). Denser sampling patterns shuld therefre help t reduce dredging csts. Efficient use f limited financialresurces fr aquatic mnitring is pssible usingthis gestatistical apprach, that is,by chsing predefined sub-areas basedn thebestavailable knwledge f thearea tsample. Cnclusins This study leads tthefllwing cnclusins. - When mnitring cntaminants and related sediment characteristics in an aquatic envirnment their spatial variability must betaken int accunt. 92

64 OPTIMAL COST-EFFECTIVE SAMPLING FORMONITORING AND DREDGINGOFCONTAMINATEDSEDIMENTS The number f sampling pints fr mnitring cntaminants in sediments can be minimized, taking int accunt the necessary accuracy, using a gestatistical apprach with predefined sub-areas. The chice fr a sampling strategy fr mnitring predefined sub-areas based n water depth, sedimentatin/ersin behavir and type f sediment results in different sample spacings. Fr example,in LakeKetelmeer a larger samplespacingfr BAP mnitring applies t thecentralpart fthelakethan near the harbr and shre, areaswith varying water depths. A prcedure is defined inthis chapter tarrive at a single sampling strategy. Frremval f cntaminants,thechice fpredefined areas isessential tadequately dredgecntaminated sediments. If spatial variability is nt taken int accunt while dredging cntaminated layers, decntaminatin f sediments will prbably fail. We therefre recmmend thrugh (althugh expensive) spatial investigatins f thecntaminated layerbefre dredging. Efficient usef limited financial resurces fr aquatic mnitring is pssible using practical, csteffective, gestatistical methds. Acknwledgements WethankPrf.S.B. Krnenberg (Delft University f Technlgy) and I.R.C. Cressie fr their editrial cmments. The technicalassistancef J.B.M.Gerritsen (Rijkswaterstaat, Institutefr InlandWater Management andwastewatertreatment) isgratefully acknwledged. 93

65 Chapter 6 In-situcnslidatinflakedepsits;anempirical mdeltrecnstructpllutinhistry J.P.M.Vink and H.J. Winkels based n: Vink,J.P.M,andH.J. Winkels In-situ cnslidatin f lakedepsits:an emperical mdel t recnstruct pllutin histry. Water Res. Bull. 30:

66 In-situcnslidatinf lakedepsits; anempiricalmdelt recnstruct pllutin histry Abstract - In the past, much effrt is put in the develpment f sphisticated mathematical mdels, describing settlement and cnslidatin f water depsited sediments. Such mdels ften aim at cmpleteness and accuracy in mdeling the physical prcesses invlved. Hwever, as a resultfthe generalityf the descriptins, the mdelsften fail t cmputelcalcircumstances satisfactrily. In specific cases, the empirical apprach may prve t be highly cmpetative and reliable. In large water bdies in the central part f the Netherlands, the alluvial "Usselmeerdepsit" is a cmmn type f fresh water sediment. Its depsitin and settlement started in 1932, when anthrpgenic activities changed the physical and chemical cnditins f the lakes drastically. Five representative cres f this sediment were taken in deep znes f the lakes.peridic waterdepth surveys verthelast sixty yearsat theselcatinsprvided infrmatin n the net sedimentatin rate and the ttal thickness f this IJsselmeer-depsit at knwntime intervals. In rder t calculate a time-equivalent fthe depthscale, crrectinfactrs fr sil cnslidatin are intrduced. A decrease in the ttal thickness f individual sediment layers is prprtinal t the decrease f its vlume, which is derived frm in-situ characteristics.crrectin factrs arebased n asimplificatin fvariusstagesfcmpressin (i.e. 0%, 30% and 45%). A factr n, which represents changes f water cntent f the sediment as a dependence f clay cntent, is derived fr each layer, allwing an inversecalculatin prcedure t determine the initial, uncmpressed thickness f each layer. Hence, a fairly reliabletime scaleindepthcanbe recnstructed. Furthermre,the radinuclide activity was measured in sme cres and the degree f rganic and inrganic pllutin was determined in numerus layers f all cres.cs-istpic tracers ( 137 Cs, 134 Cs) give a gd recnstructin f the last six decades f physical changes f the sediment and the degree f pllutin, assuming pst depsitinal redistributin and transfrmatin f pllutants t be negligible.theresults shwed clsecherence tcalculated time-scales. Intrductin TwlargewaterbdiesintheNetherlands,LakeIJsselmeerandLakeMarkermeer (Fig.6.1a,b),accumulatesubstantialamuntsfsuspendedslidssuppliedbyriverIJssel, anrthernbranchf therhine. In undisturbed areas, the sedimentatin pattern will fllw the natural chrnlgical (undisturbed) sequence.theseareasmayprvideuseful infrmatin nphysicalandchemicalchangesfthe sedimentthathaveccurredvertime (VinkandWinkels, 1991;Beurskens et al., 1993). Thesedimentatin rate is especially high in deep parts and sandpits and therefre prvides a reliable imagef transitinsfthesedimentindepthandtime. Ifregulardepthsundingsareavailableintime (yr),changesinwaterdepth (m)maybetranslated 97

67 CHAPTER 6 Nrth Sea i i -r i i i i c CO ^ Wadden Sun SP"l974Vl.560 y i r- 1 - G E R M A N Y _550j/ \.540 \ i J XStaveren SP 1959\^ Lemmer Lake IJsselmeer _ v CH EnkhuizenV SP Lake Cnstanz "rfx -jurk - S W I T Z E R L A N D A U S T R I A km,\ n Lake Markermeer \ / \ A,,, (VLelystad?, n,, 2 4 i km ; Fig Map and sampling lcatinsf the lakes IJsselmeer and Markermeer. t sedimentatin rates (m yr 1 ). Hwever, depth-time crrespndence may nt uncnditinally be derivedfrm sundings. Becausefan increasing sediment ladver time, underlying depsitswill be cmpressed, which is accmpanied bylss f pre water. This prcess is knwn as cnslidatin. Sincethe degreef cnslidatin submitted t aspecific sedimentlayerat a certaindepthis nt knwn, the time bundaries will change in time. Areliable indicatin f the specific timef depsitin therefre cannt be given. Cmplex physically-based mdelsf sediment cmpactin based nthephysicsf sil cnslidatin were, amng thers, presented by Gibsn (1958) andperrier andquiblier (1974). Althugh physical descriptins aresund,itisdifficult t btain reliable sil parameters.mrever, variatinsf experimental errrsmay superimpse anddecrease the reliabilityf suchmdels,andnemay rightly questin the general accessibility. In this study, an attempt is made t recgnize and distinguish the majr degrees f cnslidatin that ccur in thick (> 2 m) sediment layers n the basis fempirical rather than physical laws. A characteristic "water-factr" fr recently depsited sediments has t be derived. Itis ntthepurpse fthischapter tdiscusshistrical inputs fpllutants, sincethis wasdneby several authrs (Vink andwinkels, 1991 ; Beurskens et al.,1993;winkels et al., 1992). Here, wetried trecnstruct the effects f anthrpgenic activity n the gechemical histry f recent lakedepsits, and t intrduce a reliable time saving, cst saving (as ppsed t istpic dating) calculatin prcedure fr the dating fsediment layers inaquatic sediments, based n cnslidatin due tsediment lads. 98

68 IN-SITU CONSOLIDATION OF LAKE DEPOSITS; AN EMPIRICAL MODEL TO RECONSTRUCT POLLUTION HISTORY Methds Brings and sampling The sediments f the freshwater Lake IJsselmeer are mainly f hlcene rigin. Half f the ttal lake bttmareais cveredwith marinesands. After the enclsuref this lakefrm theseain 1932,salt cncentratins gradually decreased and a lamy sediment, the Dsselmeerdepsit, was depsited in freshwater cnditins. Sediments were partly prvided by the river IJssel, an ffspring f the Rhine, and partly by internal redistributin (seechapter 3).Tday,nearly 25%f the lakebed iscvered with this typef sediment. Thettalvlumefthissedimentisestimated t be280 x 10 6 m 3 (apprximately 160 billin kgdrymatter),whichwasdepsited at amean netratef0.017 m/yr (VinkandWinkels, 1991). Sand pits,which riginate frm large scale sand extractins fr public wrks,likethe cnstructin f dikes, have beenfilled naturally withthisclayey, freshwater depsit. Figure6.2 shwsveran 18km sectin hw the deep parts f Lake IJsselmeer have been filled since 1936, when the first depth sundings f this area were made. Nte the variatin in sedimentatin rates in successive time intervals. Fr sediments fund in a frmer ersin gully in the central part (in the fllwing text referred tas "channel";in Fig.6.2 indicated withthearrw), asimple and reliable sedimentatin rate mdel culd be fitted frm the data: D = t 3 (crrelatin r =0.994) in which D is the layer thickness (m) and tis thetime in years. Water depth (m BSL) sampling lcatin WARNS ) WARNS / ANOUK J? i" " S \ \ if J Distance (km) s L Fig Sedimentatin prfile ver an 18kmrw inlakeijsselmeer. The sampling lcatin inthechannel is indicated by the arrw. 99

69 CHAPTER 6 Fur lcatins in Lake IJsselmeer (Fig. 6.1b; three sandpits, "SP"and a deep part f the channel, "CH") were selected fr sampling.an additinal sampling site waschsen inlakemarkermeer, "G", whereindividual layersf sedimentin afrmer ersingully weresampled and 134 Csand 137 Csdated. The sandpits inlakeijsselmeer riginatefrm different time perids: 1940,1959and All lcatins wereat afair distancefrm each ther (5 kmr mre) andcntain a thick (> 2 m)sedimentlayer. Sediments f these lcatins were sampled inoctber 1989frm ashipwithanaugerin cmbinatin with a histing crane.waterdepthvaried frm 4-6m. Layerswere sampled in0.25 m increments, except fr the tp ( m) and deeplayers (0.50 m stepwise).sampleswere stred in glass jars and sealed and analyzed fr clay,rganic matter and lime cntent and several rganic and inrganic pllutants (As,Cd, Cr,Cu, Hg, Ni, Pb, Zn, mineral il,extractable rganicchlrides, andpcb 28, 52,101, 118, 138, 153, 180). Cncentratins were crrected accrding t Dutch standards, which implies the standardizatin t 25%clay and 10%rganic matter (Vink & Winkels, 1991; Winkels et al., 1992). Cnsequently, cncentratins frm sil layers with different physical characteristics may directly be cmpared. Frm all lcatins,histrical sunding data were cllected. Calculatins and system cnditins Cnslidatin f sediment layers isthephysical result f adecreasing specific vlume (cm 3 /g)due t lss f pre water. Smits et al. (1962) were the first t describe by a great number f bservatins a relatinship between the specific vlume and the clay and rganic matter cntent in the subaqueus depsits frm the IJsselmeer which were water saturated. Therelatinship with the water cntent can beexpressed in itsmst general frm by: With: A = c + n (L + bh) (1) A = Watercntent (g/100g dw); c = Cnstant,whichrepresentsthewatercntentf a puresandy sil withutclayrrganicmatter; n = Waterfactr, whichrepresents theinfluence f clay cntent nthewater cntent A; L = Clay cntent in weight %; b = Weightfactr fr the influence f rganic matter cmpared tthatf theclay cntent; H = Organic matter cntent inweight %. Thevaluesf thecnstants c (20)and b (3)wereempirically determined using a largedata set.fr the cnstant b, Znneveld (1960) calculated a value f 4 fr inundated sediments in the Biesbsch delta, the Netherlands,andattributedthisvalue t a lwerlevelfdecayf the rganicmatterin thissil. The degreefdecay desplay asignificant rleinthewaterretaining capacity f rganicmatter, as iscnfirmed bymanyauthrs (Suffet andmaccarthy, 1989; Schwartzenbach et ai, 1993). In 1973, De dpper stated that fr the types f sediments fund in the IJsselmeer area a value fr b f 3is plausible, prvided there aren additinal peat rplantsremnants fund. Iftherganic matter cntent is greater than 12%, a valuef 4 seems mrereliable. Specific vlume SV and water cntent A are inversely related, and are a functin f the specific weight SW(g cm" 3 )ftheinsitusediment. SW is calculatedthe cnventinal wayassplitfractins fr rganic (SW~ 1.50 g cm 3 ) and inrganic (SW~ 2.65 g cm 3 ) cntents fr each layer increment. Within theclay and rganic ranges f theijsselmeer depsits, a linear crrelatin between SW and SV is assumed. Cnsequently, ne may transpse variatins f initial (recently depsited) and ultimate (cnslidated) specific vlumes tvariatins in layer thickness. Hence: 100

70 IN-SITUCONSOLIDATION OFLAKEDEPOSITS; AN EMPIRICAL MODELTO RECONSTRUCTPOLLUTION HISTORY With: d u sv Intial layer thickness (m); Ultimate layer thickness (m); Initial specific vlume (cm 3 g" 1 ); Ultimate specific vlume (cm 3 g" 1 ); di : d u = SV, : SV U (2) Fr each layer, the relative lss {(d r d^ld^) 100%may be calculated. Td this,each sediment layer hast betreated as a yung,recently depsited sediment with itswnspecific «-factr, ÔA (watercntent)/ôl (clay cntent).hwever, arepresentative r best estimate valuefr this «-factr isntknwn fr yung r recently depsited aquatic sediments, since the suspended slid/sediment bundary is a diffuse ne.in turbulent systems,this bundary may be asthick as 0.05 m (Vink and Winkels, 1991). Therefre, the 0.05 m tp layer is nt included in this cnslidatin calculatin prcedure. It is assumed, that the «-factr in the secnd layer, m, will prvide a fair estimate fr a first apprach. Calculatins were carried utfr each f the threeusselmeer sandpits, the channel and the frmer ersin gully f Lake Markermeer. Results are presented in Figure 6.3. Fr stable sediment, which isntcnslidated and nt subjected t resuspensin, then-factr has a valuef apprximately 4.7.It shuld bented thatthis value applies slely tthesetypesf clayey aquatic sediments. Athin, sandy layer (3.2% clay, 0.8% rganic matter) in sandpit 1974 des nt seem t fllw the suggested empirical laws.this datapint isntprcessed in therectilinear ptimizatin. Relative cnslidatin (%) A Ai RC = n r = n = 42 + channel A 1940 O D gully n-factr Fig Relativecnslidatin perlayerinthreesandpits, a channel (Usselmeer) and anersin gully (Markermeer) as a functinf the n-factr. 101

71 CHAPTER 6 The calculatin prcedures described abve were carried ut fr the data that were btained frm the sediment f the frmer ersin gully f Lake Markermeer in 1989.Ten years earlier, in 1979, the very same lcatinwassampledbyanddescribedby Ente (1981). Identical sedimentatin ratesincrrespnding time intervals f the tw lcatins were assumed. This assumptin seems justified, since the ttalthicknessf sediment in thisgully hasincreased with0.1 min 10 years,which isf thesame magnitude asthemean sedimentatin rate statedbefre. Tables6.1 and6.2 areexamples f thiscalculatinprcedure,carried utfr the sampled lcatins. Next t sediment parameters, the successive mdel parameters arecalculated (eq. 1), resulting in a lssfthickness f each layer. Avaluef4.7 wasassigned t the initial n-factr. Table 6.1. Physical characteristics andcalculated parametersfrm the ersin gullylakemarkermeer, sampled in Depth (m) Thickness (m) <2^m Org. matter %dry matter A-fig n factr Spec. vlume A-fig initial Spec. Initial vlume thickness Range end (m) (m) Lss (%) Ttal thickness : Relative lss 2.78 m 31.7 % Table 6.2. Physical characteristics andcalculated parameters frm the ersin gully LakeMarkermeer, sampled in1989. Depth (m) Thickness (m) <2^<m Org. matter %dry matter A-fig n factr Spec. vlume A-fig initial Spec. Initial vlume thickness end (m) Range (m) Lss (%) Ttalthickness : Relative lss 3.14 m 36.3 % 102

72 IN-SITUCONSOLIDATION OFLAKEDEPOSITS; AN EMPIRICALMODEL TO RECONSTRUCT POLLUTIONHISTORY The intrductin f a time scale: inverse cnslidatin The relative lss f thickness f a specific sil layer is expressed in equatin 2 (last tw clumns f Tables 6.1 and 6.2). Likewise, ne can transpse a cmpressed layer t its riginal thickness prir t cmpressin, such as ((dj(d u -d^) 100%. After prcessing all cnslidatin/depth calculatins (51 bservatins),threemajr degreesf cnslidatin weredistinguished asdepth dependant variables: 1) 0% Cmpressin is submitted t the upper m layer. The tp 0.05 m is nt taken int accunt fr reasns described befre; 2) A 30%cmpressin fr mlayer depth; 3) Amean 45% cmpressin fr layers deeper than 0.75 m; The initial layer thickness D t isnw expressed as: A = I<K-y (3) in which ôd n is the thickness f the cnslidated layer increment andy is the reciprcated degreef cnslidatin. The value f j n may vary between 1 and, theretically, 100but will rarely exceed 3in natural situatins. Fr simplicity (n is finite) this series is reduced t ôdj ƒ, + ôd 2 j 2 + ód 3 j 3, using the values 1 (100/(100-0)), 1.43 (100/(100-30)) and 1.82 ((100/100-45) fr./',, j 2 andy^, respectively. Fr the Markermeer lcatin j 3 = 1.67,since maximum cnslidatin isntyet reachedbecausef insufficient layer thickness (sediment lad).fr each time interval, the cmpressed sil layers are "expanded" t theirriginal thicknesses.this apprach enablestherecnstructin f sedimentatin ratesinunknwn time intervals, such as in the channel. Calculatins prved an initial depsit thickness f 1.07 m (uncmpressed),which was cnslidated t0.77 min 1936, andhasreached a thicknessf 0.6 m in Therefre, the 1936 bundary lineis submitted t0.6 m abvethe underlying pleistcene sand layer.this "backstripping technique"isused taccuntfr cmpactin duetprgressive burial f sediments. The prcedureresulted in a depth-dependent timescale,fwhich smeexamples will be discussed. Radinuclide time tracing T testthe usef themdeltdate pllutin depsitins, a cmparissn with thermeansfhistrical datingwas carriedut.severalauthrs (Rbbins and Edgingtn, 1975;Beurskens et al.,1993) reprted n sediment timedating with theusefradinuclides.therefre, the activity f varius radinuclides ( 134 Cs, 137 Cs, 226 Ra, 210 Pb/ 210 P) were measured in 7 subsequent layers f the sediment frm the frmer ersin gully in Lake Markermeer. Up t 17 hurs cunting (analytical detectin limit = 1 Bq kg 1 ) f gamma-activity in 7subsequent sediment layers (0-0.05, , , , , and m belwlake bed)were measured with a caxial germaniumdetectr in cmbinatin with a multichannel analyzer. Relevant time marks fr 137 Cs are 1953 (first largescale appearance), 1959 (first fallut maximum caused by nuclear testings), 1963 (secnd fallut maximum) and 1986 (Chernbyl pwer plant accident and first elevated 134 Cs activity). If cmpared with r-spectra (activity amplitude) afair indicatin f the timef depsitin can begiven (Fig.6.4).It appeares that 226 Ra can nt be used as a tracer. Activities f this radinuclide remain cnstant ver time, whichisattributed t a prbable absencef (industial) 226 Radepsitin frm the river Rhine int Lake Markermeer. 103

73 CHAPTER 6 Results anddiscussin In Figure 6.5 it is shwn hw the degree f cnslidatin isprprtinally related tdepth (verlying layer thickness). Within the decade , an additinal net sedimentatin f 10.0 cm culd be bserved. Due t increasing cnslidatin, the graph has mved alng the x-axis. Settlement f sedimentsappears t beactivein the upperlayers, whereasinthe deep partsmaximumcmpressinfr this sediment layer thickness is apprached. Ahistrical recnstructin by meansfinversecnslidatin calculatins and radinuclide ( 137 Cs) dating shw remarkable cherence (Fig.6.6). In essence, these methds have adifferent apprach; in the inverse calculatin prcedure, the sediment layer depth at agiven time is the unknwn parameter, whereasin the radinuclidedating the time is a variable, and has t be interplated betweenknwn fallut maxima. 50 Cntent, Bq/kg I r 1 / "» 1»"I» 1--»-v t Depth (m) , > Ra Cs Cntent, Bq/kg 210 Pb 134 Cs 7 Cs Fig Radinuclide measurements in sediment layers (tp) and subsequent timedating (belw). 104

74 IN-SITUCONSOLIDATION OFLAKEDEPOSITS; AN EMPIRICAL MODELTO RECONSTRUCT POLLUTION HISTORY Relative cnslidatin (%) Vink & Winkels Depth (m) Fig Relative cnslidatin as a functin f depth in a frmer ersin gully in Lake Markermeer. Data frm 1979 (Ente, 1981)and 1989 (Vink and Winkels, 1991)wereprcessed accrding t thethree-step cnslidatin mdel and shw clse crrespndence t first rate regressin (crrelatin cefficient =0.99 and 0.95,respectively). Depth (m) :? _i_ Calculated Year 137, Cs-dated Fig Sediment dating accrding t the inverse cnslidatin prcedure ( ) and accrding t the radinuclide,37 Cs (O). Ntethevariance (bars)fthe datapints btained withthelastmethd whichisaninevitableresultf sediment layer thickness. Dating is based n interplatin between knwn fallut ptima. This technique f using radinuclides wasapplied by Rbbins and Edgingtn (1975) t date sediment layersin Lake Michigan,U.S.A.with 210 Pband 137 Cs,whereasBeurskens et al. (1993) used 134 Cs and 137 Cs t establish the 1986 and early 1960's time markers in sediments f Lake Ketelmeer, the Netherlands. A recnstructin f physical transitins f the sediment in time is shwn in Figure 6.7A. Nte the significant decrease f clay cntent in time, represented by the area left f the < 2 fim line.vink and 105

75 CHAPTER 6 Depth (m) Year Depth (m) 0 B! Year i Texture Sediment fractin (% dm) Hg! i Cntent (mg/kg dm) 1936 Fig A histrical recnstructin f (a) physical transitins f the sediment and (b) degree f pllutin. Winkels (1991)andWinkels et al. (1992) ascribedthis phenmenn taltered hydrlgical cnditins duethuman interference during thelast sixdecades. Figure6.7bgivesanarbitrary examplefthe pllutinhistry flake Dsselmeer (hererepresented by mercury). The vertical lines represent Dutch envirnmental quality standards. Cncentratin prfiles and trendsagreewith findings f Beurskens et al. (1993)andWinkels et al. (1992)frm sediment f Lake Ketelmeer, which hasan pen cnnectin tlakeijsselmeer. Whendataf sedimentatin histryare available, theinverse cnslidatin prceduremay prve t be a reliable, timesaving andfinancially beneficial methd fr time-dating waterdepsited sediments. Fr water depsited sediments, a characteristic n-factr may be derived as a representative value fr recently depsited material. As far as reliability is cncerned, the empirical apprach may in many cases prvetmatch any cmplex physically-based mdel. 106

76 Chapter 7 Dilutinfriverineheavymetalinputby resuspensinandalgalgrwthinlakeusselmeer, thenetherlands H.J. Winkels,G.Blm, S.B. Krnenberg andl. Lijklema based n: Winkels,H.J., G.Blm, S.B. Krnenberg and L.Lijklema Dilutin f riverineheavy metal inputby resuspensin and algal grwth inlake Usselmeer, thenetherlands. Submitted t Water Research. 107

77 Dilutinf riverineheavymetal inputby resuspensin and algalgrwthin LakeIJsselmeer, the Netherlands Abstract - Thisstudyevaluates theeffects f sediment ersinandprimaryprductin n the tempral and spatial variability f heavy metals cncentratin in settling slids in lakes IJsselmeer and Ketelmeer. Measurements in sediment cres shwed that heavy metals cncentratins in depsits frm the river IJssel, a branch f the river Rhine, are 2-3times lwerin Lake IJsselmeer than they areclsetthe river muth, inlake Ketelmeer. Settling slids were sampled frtnightly using sediment traps at tw sites in Lake IJsselmeer and cntents f clay, rganic matter, calcium carbnate, six heavy metals and ó 13 C and ô 18 0valuesweremeasured.Wind speed anddirectin, suspended slids,rganicmatter, chlrphyll, phaephytin and xygen cncentratins were measured in the water cmpartment, as was ph, temperature and Secchi depth. Regressin and multivariate analyses were usedtevaluate the relatinships within the data set. Principal cmpnents analysis and stepwise multiple regressin shwthat thevariatin intheheavy metals cncentratin in settling slids is related t the windspeed and clay cntent, bth variables that are related t ersin fsediments;and t ph, chlrphylland CaC0 3,whichare relatedt algalgrwthin the lake. This supprts the hypthesis that the spatial gradient in the heavy metals cncentratins in depsited slidsin LakeIJsselmeer is the resultf dilutin fcntaminated sediments duet ersinflder, lesscntaminated sedimentsand primaryprductin related talgalgrwth. Intrductin Inaquaticecsystems,cyclingfnutrients,rganicpllutantsandheavymetalsisften dminatedby theprcessesresuspensin, sedimentatinandhrizntaltransprtfsediments (HâkansnandJanssn, 1983;Lijklema et al, 1994).Theclserelatinshipbetweenthefatefpllutants andsediment transprt is due t the affinity f cntaminants fr particulate materials. In many river basinswith upstreaminputsfcntaminants,sedimentatinfcntaminatedsuspendedslidshasresultedinhigh cntaminantcncentratinsinbttmsedimentsinareaswithlwflwvelcitiesandturbulence.this isclearlysinthedeltaftheriverrhine (Winkels et al., 1992). TheriverIJssel, abranchftheriverrhinewithanaveragedischargef300m 3 /s (BlmandTet, 1993),flwsviaLakeKetelmeer (38km 2,averagedepth3.5m)intLakeIJsselmeer (1136km 2,averagedepth4.7m).Intheperid theriverRhinewasheavilyladedwithheavymetalsand rganicmicr-pllutants.settlingfcntaminated slidshascreated alayerfheavilypllutedsedimentsinlakeketelmeerwithanaveragethicknessf0.55 m (apprximately 15 millinm 3 ) (Winkels et ai, 1990;Beurskens et ai, 1993 and1994). CntaminatinfdepsitsinLakeIJsselmeer,whichis areservirfrdrinking-waterprductinandaninternatinallyrecgnizedbreedinggrundfrwaterfwl, hasbeen shwnby several authrs (VanEerden andzijlstra, 1986;Berger and Sweers,1988; Vink and Winkels, 1991).Hwever the cncentratins f cntaminants in these depsits aremuch 109

78 CHAPTER 7 lwerthan thsein LakeKetelmeer.This raisedthe questinfwhethermixingfcntaminated slids discharged by the river IJssel with sediments frm ther surces culd accunt fr the bserved decrease in thecntaminant cncentratin inthe dwnstream directin. A sediment andcntaminant massbalancefr Lake Ketelmeer (Ten Hulscher et al, 1992) shwed theimprtancefersinfsedimentsdepsitedin previusdecadesfr thewaterqualityf thislake. Nwadays the cncentratins f cntaminants in the slids transprted by the river IJssel t Lake Ketelmeer are lwer than thse f the lake's bttm sediment. Blm and Tet (1993) develped a sediment transprt mdel fr Lake Ketelmeer t simulate sedimentatin, resuspensin and hrizntal transprt f slidsby flw. Using asinput data thecntaminant cncentratin inthe slids discharged by the river IJssel,they were abletreprduce changesinthecntaminant cncentratins inthewater cmpartment and bttm sediment quite well in additin t mdelling the physical transprt fluxes. Althugh Lake Ketelmeer is much smaller and shallwer than Lake IJsselmeer, sediment ersin in LakeIJsselmeer might still influence thebserved spatial gradient incntaminant cncentratins. Kelmans andlijklema (1992)cncluded thatprimary prductin intheeu trphic LakeVlkerak- Zm decreasesby dilutin thecadmium cncentratin in the (ttal) suspended slids. Insummer, primary prductin in the central part f Lake IJsselmeer is high, which increases the rganic matter cncentratin in the water and als the prductin f carbnates (Del Castill and Salmns, 1986; Winkels et al, 1992; Hgeveen, 1995). S primary prductin may be a factr cntributing t the decrease f cntaminant cncentratins inthe suspended slids inlake IJsselmeer. Tempral and spatial changes in the suspended-particulate cntaminant cncentratins are usually mnitred by centrifuging ut suspended slids in water samples. Settling slids are sampled by cllecting material in sediment traps (Ten Hulscher et al, 1992,Salmns and De Grt, 1978;Van der Weijden and Middelburg, 1989; Heymen, 1990; Hgeveen, 1995). Blm et al. (1992) pinted utthat cntaminant cncentratins in settling slids, cllected with sediment traps, may differ frm cncentratins in suspended slids, btained by centrifuging. These differences are related t differences in fall-velcity distributin, which are in turn related t differences in particle size distributin and in rganic matter cntent between suspended and settled slids. Hence affinities and adsrptin capacitiesn aunit weight basis will alsdiffer fr suspended and settled material. Our bjective was t evaluate the effects f sediment ersin and primary prductin n the tempral and spatialvariability f heavy metals cncentratin in settling slids inlake IJsselmeer. Research area and methds Research area Dutch reclamatin activities during the last century resulted in several freshwater lakes being created inthe central part f the Netherlands.LakeKetelmeerbecame a wide river muthf the river IJsselas aresult f thecnstructin f tw plders:thenrthern bundary is a plder dikecnstructed in 1938; the suthernbundary a plder dikethatwascmpleted in LakeKetelmeer hasanpen cnnectinwithlakeijsselmeer.lakeijsselmeer (Figs. 7.1Aand 7.IB),createdin 1932bydammingthefrmermarine/brackish Zuiderzee,isnef Eurpe's largestinlandfreshwater bdies.it is ashallw lake with a bttmfmainly sandy sediments that hashigh net ratesf sedimentatin ffine settling slids in its deeper parts (Vink and Winkels, 1991 and 1994). Zuiderzee (Zu) depsits are defined as marine/brackish sediments (in this lake mstly sandy) that were depsited in the perid This Zu-depsit can be identified by the presence f shell fragments (Mya arenaria). IJsselmeer depsits (IJm),defined as the freshwater sedimentsdepsited since 1932, have beenpartlyprvidedby 110

79 DILUTION OF RIVERINE HEAVY METAL INPUT BY RESUSPENSION AND ALGAL GROWTH IN LAKE IJSSELMEER, THE NETHERLANDS k Fig Map and sampling lcatins inlake IJsselmeer. the river Ussel, but internalredistributin hasalsaffected thesediment cmpsitin (Ente, 1981). The IJm-depsit cvers the deepest part, which is 25% f Lake IJsselmeer, while the sandy Zu-depsit cvers theremaining-shallwer-75% f the lake bed. During the summer primary prductin in Lake IJsselmeer is reflected by an increase f rganic mattercntentand theccurrencefalgal blms (Hgeveen, 1995), leading t a highcarbnatecntentf sediments (Winkels et al, 1992). Sampling and chemical analyses Frm 1 April t 7 December 1992, samples were taken frm tw bservatin platfrms in Lake IJsselmeer lcated atdifferent distances (Z, and Z 2 ; Fig. 7.IB)frm theijsselmuth. Z, (waterdepth 6.4 m) was lcated in the central part f the lake and Z 2 (water depth 5.2 m) in the suth, near Lake Ketelmeer. Water samples were cllected autmatically every week and settling slids, cllected in sediment traps,were retrieved and analysedfrtnightly. Settling slidswereals retrievedandanalysed mnthlyfrm the river Rhineat Lbith (apprximately 150 km upstreamfthe Rhine's muth),n the Dutch-German brder. Settling slids were sampled atlbith thrughut the whle f Heymen (1990) prved thatheavy metal cntaminatin inthe river Rhineis als representative f the cntaminatin f theriverijssel. Sedimentmaterialwas cllectedfr analysiswithsix 60-cm-lng cylindricaltrapsf 6 cmdiameter lcated at mid-waterdepth. The trapswere emptiedeverytw weeks.after the trapswere emptiedand their cntents transprted t the labratry, resuspended material was allwed t settle fr 24 hurs at 4 C befre the supernatant was siphned ff. The samples frm the sediment trap were then immediately frzen, freeze-dried and stred. Usual prcedures (Hfstee, 1983) were used t analyse sample material, which hadbeen hmge- 111

80 CHAPTER 7 nized, fr clay fractin cntent (Clay), rganic matter cntent (OM), carbnate cntent (CaC0 3 ), suspended-slidscntentinsedimenttrap (SSsed), rganicmatterinsedimenttrap (OMsed), andcntents f cadmium (Cd),chrmium (Cr),cpper (Cu),nickel (Ni),lead (Pb)and zinc (Zn).Carbn ( 12 Cand 13 C) and xygen ( 16 0 and 18 0) cntent were analysed by treating the samples with 95% (v/v) phsphric acid slutin and measuring the liberated carbn dixide by mass spectrmeter accrding t standard prcedures (Mk and Grtes, 1973). The water samples were analysed by usual prcedures (Hfstee, 1983) t determine suspended slids (SSw), rganic matter (OMw) and ph. Chlrphyll-a (CHL) and phaephytins (PHA) were extracted with acetne and measured by a Beekman (Fullertn, CA) DU-64 spectrphtmeter accrdingt Glterman et al. (1978). In thefield disslvedxygen (0 2 ) and temperatue (T) were measured at mid water depth with an ampermetric xygen electrde (54-ARC, Yellw Springs, USA), and Secchi-disk depth (Sd) wasmeasured with awhite disk with three large circular hles in it.wind speed (Wind)and directin were btained frm anearby meterlgical statin. Calculatin fô' 3 C and ô' s O Duringphtsynthesis, algae preferentially use thelighteristpefcarbn ( 12 C0 2 )inaquatic ecsystems,causing an enhanced relativecntributin f <5 13 C (ô 13 C) t CaC0 3 precipitates (Lynch-Stieglitz et al., 1995), which are a result f the increase f the ph induced by algal grwth (Mk, 1970;del Castilland Salmns, 1986). Mineralizatin fdeadalgae will, nthe therhand,resultin adecrease f (S,3 C valueinthe IJm-depsits. Higher ó 13 C valuesals indicateanaquaticsystemwith a highersalt cntent (Salmns et ai, 1975). The rati f 18 0 t 16 0 is related t precipitatin and evapratin and shuld therefre shw seasnality.precipitatin leadstanincrease,andevapratin t a decrease,fthis rati (Salmns et al, 1975). The ratis f carbn and xygen istpes are usually evaluated by calculating the relative deviatin frm that f a standard (PDB) reference valuefr carbn and xygen: ÔX(% C )= Rs ' Rst -IP 3 (1) Rst With: X = 13 Cr 18 0, respectively Rs = 13 Ct 12 C ratir 18 0 t 16 0 rati,respectively, fr the sample Rst = astandard ratifr carbn (PDB seawater: -1.06%c)rxygen(PDB sea water: -4.14%c),respectively. Nrmalizatin f cncentratins Tstudy variatins in timeand spacef cntaminant cncentratins,differences in adsrptin affinity f thecntaminant particles shuldbeaccunted fr. Thiscan be dneby standardizatin withrespect t the cntents f the different adsrbing cmpnents in the suspended slids. Gechemical phases such as clay minerals, irn xides and hydrxides, manganese xides and hydrxides, and rganic matter are the principal adsrbents f heavy metals (Singh and Subramanian, 1987; Kelmans and Lijklema, 1992). Hwever,all xidesand hydrxideswere ntanalysed.thus theheavymetalcntents werenrmalizedperunitweightfclay (indicatedbycc, similart ccd)andrganic matter (indicated by C, similar t Cd).Bth the riginal and nrmalized data were used fr the study f heavy metal cncentratins inrelatin tther characteristics measured. Based n the cntentfeachheavy metaland itsaveragevalueduring 1992ateach lcatin, asum f heavy metals (XHM) can be calculated fr all six heavy metals studied. Similarly, XHM and 112

81 DILUTION OF RIVERINE HEAVY METAL INPUT BY RESUSPENSION AND ALGAL GROWTH IN LAKE IJSSELMEER, THE NETHERLANDS XcHM represent the sum f nrmalized heavy metals cntents fr rganic matter and clay cntent, respectively. Input flux calculatin T evaluate the impactnlake IJsselmeerf the heavy metal lad f the riverussel, theladperunit surface area (areiclading)wascalculated.thisaverageareiclading flux, Afly,iscalculatedfrm the mnthly valuesf C RI, SS RI and ly. 12 2J (Lui " SS R, ly) j an With: Afly - average areic heavy-metal input flux (mg C nr 2 d 1 ) C R, - heavy metal cntent suspended slids river (mg C kg 1 ) SS m = suspended slidscntent riverinput (kg nr 3 ) Iy = average discharge river (m 3 d" 1 ) S = area f lakes IJsselmeer and Ketelmeer (m 2 ) 1-12 = number f mnth Afly = (2) Statistics Crrelatin analysis n the data was perfrmed with the statistical sftware package SPSS (SPSS, 1996), using a ne-tailed Mest with P < Principal cmpnent analysis and stepwise multiple regressin wereals perfrmed with the package. Thesestatistical analyseswere perfrmed t identify and describe relatinships amng the measured variables.typically, this yields a large amuntfdata. Representative data aregiven inthis chapter. Resultsanddiscussin Spatial variatin Table7.1 summarizes the means and standard deviatins f the variables sampled in settling slids at Z x and Z 2 in 1992.The values atbth lcatins are cmpared with riverrhine input (RI) near Lbith and with the entire tp layer sediment (IJm-depsits andzu-depsits) f Lake IJsselmeer. These Umand Zu-depsits hadbeen sampled 4yearsearlier (Vinkand Winkels, 1991). Winkels andstein (1997) recently reprted the cntents f clay, rganic matter and heavy metals in the IJm-depsit f Lake Ketelmeer. These cntents are similar t the river-inputcncentratins (RI) given in Table 7.1.Clay fractin and rganic matter cntents werehigher inthe sediment traps than inthe depsited sediments in Lake IJsselmeer. Organic matter cntents f river-inputat Lbith and at Z 2 are similar. Carbnate cntents and <5 13 C values were lwer in river-input,while heavy metal cntents were higher (except Cd)than in LakeIJsselmeer. Heavy metal cntents at Z; and Z 2 aregenerally similar tcntents inthe IJm-depsits buthigher than cntents in the sandy Zu-depsits.Furthermre, heavy metal cntents in the Zu-depsits were lwer than in IJm-depsits in Lake IJsselmeer. Table 7.2 summarizes the values f the variables measured inthewater. Mst values werehigher at Z, than at Z 2. A f-test (tw-tailed 95%; P < 0.01) was perfrmed n all data measured atbth lcatins in Lake IJsselmeer. The cmparisn f cntents f heavy metals in sediment traps at Z x and Z 2 makes it clear thattheheavymetalscncentratin issignificantly higherat Z 2. Mstheavymetal cntents nrmalized 113

82 CHAPTER 7 40 Cntent (%) OM 40 Cntent (%) Clay 30 30,-- Z, Rl April August December1992 April August December1992 Value ( /) Value ( /) s>3 April August Z December1992 April _j i i.i. 1 August December Cntent (%) CAC Cntent (mg/m 3 ) CHL 30 Z-, «Z * i t A 1 \ f XP April August December1992 n April 1 i i...j. I 1 August December1992 Fig Frtnightly and mnthly changes f rganic matter (OM), clay (Clay), carbnates (CaC0 3 ), chlrphyll (CHL) cntents and <5 13 C- and 18 0-values in settling slids at Z, and Zj and in river input (RI) in 1992 in Lake Usselmeer. 118

83 DILUTION OF RIVERINE HEAVY METAL INPUT BY RESUSPENSION AND ALGAL GROWTH IN LAKE IJSSELMEER, THE NETHERLANDS SI <**l "-' O O en c-j i dl m l ö ö ö ö ö ö ö ö d fil GO cil \ vd <N F \ vi O O «3?i el l «ON ^ "O mi r^l FHI fsi i w m M 00 tf) V) P P p Ö Ö O O Ö Ö Ö Ö O d ' si öl öl l O (S (N M - - p f O f ^ t N r * - ) r n p m ^ P d d d d d d d d d d d P p c H <*"> P. i r- (N p p l l d ' p ON m ^H CN m p p d d d d d p l «U Ol CI 1/1 d ö l öl P P P c N r - O N p O N * n s - ^ m r p ^ v i d d d p p p p ' l m H O -H -H d d p p P ci -H \C ^H m vi m l> p d d d d öl ö d l m m ^- p * d d p Tt r~ < ON m m p p ó ö ó ö ~ p p l 31 2 ON p p (N Tt O N * N H l l l p p p l P P N l l < O N O < ^ N D T t - m p ( N ^ V ~ ) r f N O P - - N O O p p p p ö d d d J P Ol Ol O p p p Ol «r-l th th P t"- ^1 n NO CNI r-- m *t t- NO r^ < NO 00 -H CM O P p öl öl d d öl öl d p p d P P P P P C N I ^ <N P p p d d d d d d l d 5 p p p p l <N(NPfs)(NCNm-<1-0 d d d d d d d d ï p p p p p p «tfl 33 'B c t U >/5 1^ H d V a. a O <* O S CO ö NO CN d NO d S p - d <2I ö CN. p 8 r^l M öl S öl I^N P O VO d ce! p H ni d d d 8 ^~ r- d p p >n d 001 ON g öl ^ g ' Ö p p rt U 0 U c * > 0 c / 5 0. t /? H O U u «< c U U U Z 5. N 119

84 CHAPTER 7 Table7.7. Resultsprincipal cmpnent analyses at twlcatins inlake IJsselmeer z x Factr 1 Var. Scre Factr 2 Var. Scre Factr 3 Var. Scre Factr 4 Factr 5 Var. Scre Var Scre Factr 6 Var. Scre Cd Pb Cr Zn Ni ph OMw SSw PHA CHL OM T <5' 8 0 Clay Ó,3 C CaC OMsed 0.95 S d SSsed Wind Cu 0.88 Accunts fr 84.9% f variancein dataset ^2 Factr 1 Var. Scre Factr 2 Var. Scre Factr 3 Var. Scre Factr 4 Factr 5 Var. Scre Var. Scre Factr 6 Var. Scre Factr 7 Var. Scre Pb Zn Ni Cr Clay Cd SSsed OMsed Wind T PHA 0.93 SSw 0.90 OMw 0.71 CHL OMw 0.88 (5 I CaCQ ph 0.73 Cu S d ô"c 0.59 Accunts fr 87.5% f variance indata set The affinity f the heavy metals fr rganic carbn differs significantly at Z 2 frm X x in Lake IJsselmeer. The increase f carbn atlcatin T, x has ninfluence n the adsrptin f heavy metals,but it is respnsible fr dilutin there. The influence f mainly CHL, CaC0 3 and Clay explains the behaviur f each and the sum f allheavy metal cntents at Zi during 1992.The influence f Wind, ph, Clay and partly OMw explains thebehaviur f each and the sum f all heavy metal cncentratinsat Z 2 during This suggests that besidestheeffect f river input,sedimentatin,ersin - and hence dilutin -and, t a lesser extent, als algal grwth determine the heavy metal cncentratins in the suspended slids. Cnclusins Measurements f the cncentratins f six heavy metals in suspended slids, discharged by the river IJssel, and f settling slids at tw lcatins in Lake IJsselmeer shw a typical spatial gradient. The heavy metal cncentratins decrease with increasing distancefrm the river'smuth.this spatial gradient is als fund when heavy metal cncentratins are nrmalized fr clay and rganic matter cntent. Measurements in sediment cres frm Lake Ketelmeer and the central part f Lake IJsselmeer shw that the heavy metal cncentratins in sediments, depsited in the same perids are 2-3 times higher inlake Ketelmeer. Therefre, this spatial gradient isreflected in thebttm sediment. 122

85 DILUTION OF RIVERINE HEAVY METAL INPUT BY RESUSPENSION AND ALGAL GROWTH IN LAKE IJSSELMEER, THE NETHERLANDS Table 7.8. Results stepwise multiple regressin fr heavy metals and nrmalized heavy metals at tw lcatins in Lake IJsselmeer Relatin Cd ccd Cr ccr Cu Ni Pb Zn CHL OMw CHL PHA OMw SSw CHL CaC CaC CHL T OMw SSw CHL ls d CHL CHL CaCO, + < Zi R 2 * lhm = CHL CaC Clay Relatin R 2 Cd Cr Cu Ni Pb Zn ph Wind Wind ph Clay CHL ph Clay T CHL Clay Wind ô' 3 C Wind Clay CHL IMM Wind ph Clay OMw * Crrelatin cefficients radjusted crrelatin cefficients with asignificance level f P < A simple sediment mass balance, based n data n river IJssel input and bserved sedimentatin fluxes, indicates thatthe ttal internal sedimentatin fluxesf heavy metals inlakeijsselmeer are far greater than the areic input ladf theriverint the lake. Due t the cmplexity f the relatins between measured variables, heavy metals cncentratins and variablesrelated tprimary prductin and ersin, singlecrrelatin analysis dntreveal clear relatins andprcesses thatexplain thisdilutin. Principal cmpnents analysis and stepwise multiple regressin shw that variatin in heavy metals cncentratin in settling slids is related t wind velcity and clay cntent, bth f which arerelated tresuspensin/ersin f sediments; r, alternatively, ph, chlrphyll and CaC0 3, which are related t algal grwth in the lake. Resuspensin/ersin-related variables are the dminant factrs explaining the variatin in the heavy metals cncentratin f the suthern part f the lake, whereas algal grwth-related variables explain mstf thevariatin intheheavy metals cncentratin in settling slidsfthecentral part f Lake IJsselmeer. There, where algal cncentratins are high, the negative relatin between the cncentratin f mst heavy metals in settling slids and the cncentratin f chlrphyll and rganic matter in the water cmpartment justifies the cnclusinthatdilutinfcntaminated suspended slids causedbyprimary prductin is relevant. In the suthern part f the lake, the heavy metals cncentratin is psitively related t wind velcity and clay cntent. This indicates that resuspensin f recent depsits cntributes t the heavy metals cncentratin in the water cmpartment. The gradual increase in the 123

86 CHAPTER 8 prductin related talgal grwth, andresuspensin/ersinf lder depsits in Lake IJsselmeer. In shallw lakes the internal cycling andhrizntal distributin f cntaminated sediments is ften dminated by wind induced resuspensin and hrizntal transprt f sediments (Hâkansn and Janssn, 1983;Lijklemaera/, 1994). In tw lakes in the area, LakeMarkermeer (Van Duin, 1992;Van Duin et al, 1992)and Lake Ketelmeer (Blm andtet, 1993)the mdel STRESS-2d (Sediment Iransprt, Resuspensin and Sedimentatin in Shallw lakes) was successfully applied t simulate suspended slids cncentratins and sedimentatin patterns. This mdel includes a descriptin f bttm sediment resuspensin/ersin due t wind induced waves, sedimentatin and advective and dispersive hrizntal transprt. The mdel als includes a descriptin f the effects f resuspensin and sedimentatin n the bttm sediment cmpsitin (Blm et al.,1992). The bttm mdelisbased n a 2- layer cncept.ontpf a mrer less cnslidated sedimentlayeris a thin tplayer,with a highwater cntent. This tp layer can be depleted by resuspensin in perids and areas where resuspensin exceeds sedimentatin. When the tp layer is depleted ersin f the underlying layer starts. Ersin washwever simulated in a rather simple way:with a cnstant velcity.in a situatin likeinlake IJsselmeer, where afcus n the ersin prcesses is needed, a mdel in which ersin f cnslidated sediments isrelated t thehydrdynamicfrces induced by wind ismre apprpriate. Because f the time scales f resuspensin and ersin and the effects f depth gradients n these prcesses, a sediment transprt mdel necessarily has ahigh reslutin in time and space.using such a mdel fr a perid f several decades wuld result in extravagant cmputing times. While the characteristic time scalesfr resuspensin and ersin and the resulting dynamicsf thethickness and cmpsitin f the sediment tp layer and thecncentratin in thewater cmpartment areintherder f less than anhur up t aday,thechanges in the cmpsitin f the mre r less cnslidated sedimentlayersare expectedthave a muchlarger characteristictimescale (weeksup t years). This raised the questin whether it is pssible t develp a mdel which, based n an integratin f simulated transprtfluxes in timeandspace,simulatesthe mrphlgy and cmpsitin fsedimentsnthelng term.thisstudy aims tdevelp thismdel. Afirst bjective f this studyist recnstruct the sediment (re-)distributinprcesses inthe pastin rdertevaluatetwhat extentredistributin f ld depsits has cntributed t the sedimentatin and s t dilutin f the cntaminated sediments supplied by the riverijsselin sedimentatin areasinlake IJsselmeer. This recnstructin then shuld result in an instrument fr simulatin f the changes in sediment cmpsitin and cntaminatin in the future, given the changes t be expected in the cntaminant ladsf the river IJssel. Theinstrument thus shuld describe the sediment fluxes inthe area. In this chapter an integrated mdelling apprach is discussed. Tw mdels are adapted and cmbined. The mdel STRESS-2d is mdified. Abetter descriptin f ersin is included. A new mdel, DIASPORA (Diagenesis f Aquatic Sediments anddispersin f Pllutants duetresuspensin and Sedimentatin in AquaticEcsystems) isdevelped.thismdel simulates thechangesin mrphlgy byintegrating STRESS-2d resultsbutalssimulates the changesincntaminant cncentratins due t sediment transprt inthe system. Themdel iscalibrated byusing anextensive data setincluding suspended slids measurements and bserved sedimentatin fluxes and validated by cmparing the DIASPORA results withhistrical recrdsn sedimentatin fluxes and cntaminant cncentratins in the area.this apprach and simulatin results f the cming decades arediscussed belw. Research area and methds Research area Lake IJsselmeer (Fig. 8.1) was created in 1932,by damming the frmer marine/estuarine Zuiderzee. 128

87 MODELLING DIAGENESISOFAQUATIC SEDIMENTS AND DISPERSIONOFCONTAMINANTS INLAKE IJSSELMEER Z-i /Z2 Mnitring sites fr SS, fluxes, etc. Y-i Sediments cre in the deep channel Y2/Y3 Dredging pits, created in 1959/1974 K Dredging pit, created in 1938 Hutrib One f the mnitring sites fr water level variatin Fig Bathmetry f Lake IJsselmeer area, the names and ages f the mstrelevant dikes and plders and mnitring sites used inthis study. 129

88 CHAPTER 8 Later large plders were cnstructed in the suthern part f the area. In figure 8.1 therelevant histricalinfrmatin is summarized. Thedepth gradientsinlakeijsselmeer (Fig.8.1) stillreflect the hydrdynamicfrces in the frmer marinesituatin.in the centrefthelake, wherethe widthwasrelatively small,deep tidalchannelsare still present. Nwadays these are areas with high sedimentatin fluxes and predminantly fine sediments (clay, silt), whilethe surrunding areaissandy (Chapter 1; Figs. 1.2 and 1.3). Alsthedeep pits,createdbydredgingfsandfr thecnstructin fdikes,are areaswith high sedimentatin. In the suthern part f the lake, the area near which the plders were cnstructed and in the present Lake Markermeer, brackish clay still can be fund. The majr changes in the hydrdynamics f the lake in 1932 resulted in a redistributin f fine sedimentsinthearea.ersinfclayandsilt, which was depsitedin thesuthernpartfthelake, and internal transprt due twind induced currents,are suppsed thavecntributed tdepsitin f fine sediments inthe deep areas in the lake.due t the cnstructin f plders the areas with ld clay and silt depsits were step by step islated frm the remaining Lake IJsselmeer (see Fig. 8.1). S, since 1975 the river IJssel, which always hasbeen amajr sediment surce,remained asthe sle sediment surce. The hydrlgy f the area is dminated by the inflw f the river IJssel with an average discharge f 300m 3 /s (Blm andtet, 1993). The riverwater flws vialake Ketelmeer (38 km 2, average depth 3.5m) int LakeIJsselmeer.Thrugh sluices (Fig.8.1) waterisletut int thewadden Seaat ebb tide. Due t its size and relatively shallwness (1136 km 2, average depth 4.7 m) wind induced currents dminate theflw pattern inthelake. The mdel STRESS-2d STRESS-2d was riginally develped byvan Duinand Blm (Blm et al, 1992;Van Duin, 1992;Van Duin et al, 1992).Inthe mdel the 2-dimensinal transprt equatin, including resuspensin, ersin and sedimentatin as surce and sink terms is slved numerically, using an alternating directin implicit slutin technique (Stelling, 1984). The simulated prcesses are schematically shwn in Figure 8.2. Water mvement and hrizntal transprt f slids arecmputed with the 2-dimensinal hydrdynamical mdel WAQUA (Stelling, 1984). This mdel simulates flw velcities and water levels,with in-andutflw andwind stressas bundary cnditins anddriving frces. InLakeIJsselmeer areathe maininflw is the river IJsselandutflw is t thewadden Sea, resultinginan veralladvectivesutheast tnrth-westflw nwhichwind induced circulatin flws are superimpsed. The descriptin f sedimentatin is based n well knwn cncepts (Sheng and Lick, 1979;Smlyödy, 1980; Lick, 1982; Aalderinkef al, 1984): 0 s =w s -SS (1) in which <P S is thesedimentatin flux (g nr 2 s 1 ), w s thefall velcity (m s 1 )andss thesuspended slids cncentratin (g nr 3 ). Frresuspensin and ersin amdificatin fthedescriptinbylam & Jaquet (1976) isused: <Z> r = K r (U b -U b, cr, r ) if (U b >U b, cr, r ) (2) 0 e = K e (U b -U bicr, e ) if (U b >U b, cr, e ) (3) with 0 r/e the resuspensin resp. ersin flux (g nr 2 s 1 ), K^ the resuspensin resp. ersin cnstant 130

89 MODELLING DIAGENESISOFAQUATIC SEDIMENTS ANDDISPERSIONOFCONTAMINANTS INLAKE IJSSELMEER DIASPORA STRESS-2D transprt water resuspensin sedimentatin tp layer mixed layer depsited layers underlying sediment Fig Schematic presentatin f theprcesses and cmpartment included inthemdels STRESS-2d and DIASPORA. (g rrr 3 ), U b therbitalvelcity (m s 1 )and U bcrr/e the critical rbitalvelcityfrresuspensin resp. ersin (m s 1 ). Because the minimal frce needed t erde particles frm the cnslidated bttm sediment layeris higher than thefrce required tresuspend particles frm thenn-cnslidated tp layer the critical rbital velcity fr ersin will be much higher than the ne fr resuspensin. Bth resuspensin and ersin can belimited by depletin f the tp layer resp.underlying sediment layer. The rbital velcity is afunctin f the wave height, length and perid, which in their term are a functin f wind speed, fetch length and lcal depth. T simulate the wave characteristics the CERC (1977) mdel isused, with an adapted wind speed accrding tbuws (1986). The rbital velcityis calculated with (Phillips, 1966); TTR U = - T s sinh(2 n d/l) (4) inwhich H s is thesignificant wave height (m), T s thesignificant wave perid (s), L thewave length (m) and dthe lcal water depth (m). T accunt fr the variability in sedimentatin and resuspensin characteristics (Blm et al, 1992; Lijklema et al, 1994) 5sediment fractins aredistinguished. Thesefractins are basednfall velcity distributin measurements (VanDuin, 1992;Van Duin et al, 1992). Allfractins have acharacteristic 131

90 CHAPTER 8 Table 8.1. Fallvelcity ranges f the sediment fractins. fractin 1 fractin 2 fractin 3 fractin 4 fractin i- 6 < < < w s w s w s w s w s > > > > > 311 IO IO IO 6 40 IO 6 11 IO 6 m s 1 m s 1 m s' 1 m s' 1 m s" 1 cmbinatin fresuspensin and ersinparameters (K,.,K,,, U bcrr, U b cre ) andfall velcities (w s );the latterf cursewithin thedefined fall velcity ranges fr each fractin (Table 8.1). The mass f all fractins in bth sediment layers iscalculated dynamically as afunctin f resuspensin, ersin, sedimentatin, burial and mixing between the sediment layers. Burial f sediment frm thetplayeristriggered by amaximal thickness f this layer (Klaver andvandeven, 1995). Depthgradientsin Lake IJsselmeerare lcallyrathersteep. Thus a highspatial reslutin is needed. A grid size f 250 x 250 has been selected. Tavid instability the maximal time step is 10 minutes. Frsimulatinf sedimenttransprtinretrspect fr the peridbefre thedikesand plderswere created, amre carse mdel with agrid sizef 1 x 1 km wasused.inthe areas utside thepresent Lake IJsselmeer depth changes are mre gradually, which justifies the use f a carse grid. The Lake IJsselmeer mdelisnested int the carse mdel. Observed wind speedsanddirectins and estimated inflws and utflws derived frm a water balance based n measurements in the majr inflws and utflws and data n the water level variatin in the lake, are used as hydrdynamical bundary cnditins. The suspended slids cncentratins in the inflws are taken frm literature. The initial cncentratins f the sediment fractins in de sediment were measured at sme sites and then extraplated based ninfrmatin nthe spatial distributin f different sediment types inthe lake. The mdel DIASPORA Themdel DIASPORA simulatesthechangesinmrphlgy andcmpsitin f thesedimentsin the lake ver alng perid; years up t decades. The mdel isbased n the assumptin that the sediment cncentratin and cmpsitin inthewatercmpartment andin thetplayerarevery dynamic, butthe effects f this rapid sediment-water interactin n the thickness and cmpsitin f the underlying sediment layer are minimal n a small time scale.thus fr this layer the integrated net effects ver a lngerperid arerelevant. Tsimulate thechanges incntaminant cncentratins due t sediment transprt, sediment classes are used. These can characterize sediments present in the initial situatin in different areas within the lakeaswellassedimentssuppliedby incming riversin varius perids. Thismakesit pssiblet trace the redistributin f ld depsits with lw cntaminant cncentratins and tevaluate the distributin pattern f incming slids, with cntaminant cncentratins varying in time. These sediment classes thus represent sedimentswithvariusquality.superimpsed n this subdivisin with respecttquality is a physical subdivisin in 5 fractins, which is used in STRESS-2d. This physical characterizatin distinguishes settling rates, resuspensin and ersin cnstants and critical rbital velcities. In DIASPORA the cmbinatin f thesetwclassificatins isused, leading t amatrix which cmbines cntaminatin- andtransprt-characteristics (quality classes superimpsed upn "size"-fractins). LikeinthemdelSTRESS-2d severalsedimentlayersare distinguished (Fig.8.2). Due t theintensive transprt between the water cmpartment and the sediment tp layer the cncentratins f sediment classes in bth these cmpartments are clsely interacting. It can be shwn that in a statinary situatin in a wellmixedcmpartment the relativecncentratin feachfthe sedimentclasses is the 132

91 MODELLING DIAGENESIS OF AQUATIC SEDIMENTS AND DISPERSION OF CONTAMINANTS IN LAKE IJSSELMEER weighted average f theirrelativecntributin t theincming fluxes. Frthe water cmpartment this is: T + A 0 + A 0 Xm(T ij + A0 r>ij +A0 e, ij ) with C wi j the cncentratin in the water f quality class j f "size"fractin i (g nr 3 ), Ti,j the lad by hrizntal transprt (g s -1 ), A the surface area f the cmpartment (m 2 ), 0 rij theresuspensin flux f class j f fractin i (g nr 2 s _1 ) and 0 ei j theersin flux (g nr 2 s 1 )- m is me sum f r m classes effractin i.equatin 5is slved fr allfractins f all sediment classes. In the mdelthenlyincmingflux inthe tplayeristhesedimentatinflux. Thusthe relativecncentratinfeachclassin aspecific sediment fractin is equalt the relativecncentratin in thewater cmpartment. Under the tp layer a secnd layer is defined. It is assumed t be well mixed due t bilgical activity.thethickness f thislayer is estimated n the basis f bserved 134 Cs/ 137 Cs-ratis in prfiles in LakeKetelmeer abutnemnthafter thechernbyl-accident (Hettling, 1987). These bservatins shwed nrati gradient in the upper 10 t 20cmf the sediment prfile. Similar results were fund inthenetherlands inhllandsendiep/haringvlietand inthe Ostvaardersplassen (Hettling, 1987). Themassf each sediment fractin andclass inthis layerisaffected bynet sedimentatin and ersin, bth fluxes at the upper bundary f this layer, and by burial f sediments in situatins with net sedimentatin fr alng perid atthe lwer bundary. In areas where ersin dminates the underlying layers can be grubbed up. The mass balance equatin fr each sediment class f a sediment fractin is: ónvij... + $.. (6) ôt in which M m ^ is the mass per unit f area f sediment class j f fractin iin the mixed layer (g nr 2 ), 0 ni j is the net sedimentatin flux (g nr 2 s" 1 ), 0 e,ij is th e ersin flux (g nr 2 s" 1 ), 0 b^ the burial flux (g nr 2 s" 1 )and 0 g y is theflux duetgrubbing (g nr 2 s _1 ). Thenet sedimentatin flux isthe difference between the sedimentatin and resuspensin flux. The flux f each class f a sediment fractin is afunctin f the ttal mass f this fractin transprted ver a bundary layer and the relativecncentratin f this sediment class in the cmpartment frm which thefluxes riginate.frinstancefr theburial flux: M with 0 b g theburialflux f class j f fractin i (g nr 2 s -1 ), mthettal number f classes andm m>i j the massf sediment class j f fractin iinthemixed layer (g nr 2 ). X(M m y) is thettal massffractin i inthe mixed layer (g nr 2 ). At user defined intervals a new layer in between the layer depsited in a previus perid and the mixed layer is created. In perids with net sedimentatin the mass within this layer increases due t burial. In perids with ersin the mass decreases due tgrubbing. In areas where ersin dminates depsited layerswill beabsent.then sedimentsfrm thelwestlayer,whichisinfinite, canbegrubbed up. 133

92 CHAPTER 8 T evaluate the effects f sediment transprt n mrphlgy and cntaminant cncentratin the mdel als has t accunt fr cnslidatin f sediments and the depsitin f internally prduced CaC0 3. Based n field bservatins (Vink and Winkels, 1991) the density f thedry sediment is estimated 2552kg m -3. Arelatinship between the prsity f sediment layers and the depth in the sediment clumn was derived: Prsity = Z (8) with Zisthe distancef the sediment layer t the sediment-water interface (m). Since abut 1950the depsitin f slids in Lake IJsselmeer has increased due t CaC0 3 precipitatin.thisisreflected in anincreasing CaC0 3 cntentindepsited sediment layers. The CaC0 3 cntentincreased frm 14%in 1950 t 37%in sediment depsited in ± 1990 (VinkandWinkels, 1991). It was assumed that the CaC0 3 prductin befre 1950 was minimal and that the CaC0 3 cntent in depsits frm that perid reflects the cntent in the incming sediment lads.the CaC0 3 prductin isaccuntedfr byintrducing a new empiricalcnstantf CaC0 3>with a value 1 till 1955and increasing gradually t 1.3 in Thettalmass within a sediment layer iscalculated as: 1 x,ttal ivi x,sed x CaC03 (9) inwhichm x ttal is thesediment mass perunitf area (g nr 2 ) in layerx. The layerst which thisapplies are the mixed layer and the underlying depsited layers. M xsed is the areal mass f the sediments (g nr 2 ) (excluding internally prduced CaC0 3 ).Itshuldbentedthat the calculatin fthickness and ttal mass in a layer is dne in the pst-prcessing stage. Bth are nt affecting the simulatin f the sediment transprtfluxes,but becme imprtantwhen theeffects fsedimenttransprtn mrphlgy andcntaminant cncentratins are evaluated. Simulatins with the mdel DIASPORA are based n the simulatin results f the STRESS-2d mdel, discussed in a previus sectin. The variables used at the mdel interfaces are summarized in Table 8.2.T slve the mass balances f the secnd and underlying sediment layer, cncentratins f all sediment fractins and classes in the water cmpartment and sediment tp layer are needed. The weekly averaged cncentratins f sediment fractins are cmputed frm STRESS-2d results. The cncentratins f sediment classes are calculated using Eq. 5. Slving this equatin fr all grid cells results in amatrix-equatin, which is slved numerically by iteratin. In the mdel DIASPORA tw different time cnstants are used t slve the sediment layer mass balances. Thesedimentmass balancef the mixedlayerisslvedwith a timestepf 1 week.given the sedimentatin fluxes within the lake (discussed later) and acharacteristic thickness f the well mixed layer f 0.15 m it can be shwn that the changes in the cmpsitin within aperid f ne week are very small. Fr the prcesses at thelwer bundary f the mixed layer (the depsitin f sediments r the grubbing f frmerly depsited layers) atime stepf 1 yearis used. Table 8.2. SRESS-2d results used in DIASPORA. C w, the weekly and spatially averaged cncentratin f a fractin i in the water (g nr 3 ) 0 S i the weekly (and usually spatially averaged) sedimentatin flux f a fractin i (g nr 2 s"! ) <P, ; the weekly (and usually spatially averaged) resuspensin flux f a fractin i (g nr 2 S"') <J> e i the weekly (and usually spatially averaged) ersin flux f a fractin i (g nr 2 s" 1 ) T a _>b. i 'he weekly and spatially averaged lad frm cmpartment a t cmpartment b, due t hrizntal transprt by advectin and dispersin, fr fractin i (g s') 134

93 MODELLING DIAGENESISOFAQUATIC SEDIMENTS AND DISPERSIONOFCONTAMINANTS INLAKE IJSSELMEER Becausefcmputing time a carsegrid ispreferable. The sizeusedis 1 x 1 km.hweverin areas with steep depth gradients and thus a high spatial variatin in resuspensin and ersin fluxes, the effects f sediment transprt n the mass and cmpsitin f the sediment are evaluated n ascalef 250 x250 m. This isdneby assuming that the water cmpartment (lxl km) is well mixed, but fr eachf the sixteen 250 x 250 mcells within this cmpartment individual sediment mass balances fr the bttm layers areslved. These are based n the lcal resuspensin, ersin andsedimentatin fluxes inthese sectins, as simulated with STRESS-2d. Field bservatins and experiments In this study suspended slids cncentratins were measured cntinuusly frseveral mnths at tw lcatins (Z 1 and Z 2 ) in LakeIJsselmeer (Fig.8.1). At bthlcatins the cncentratinsfthesediment fractins inwaterweremeasuredregularly. Themethddescribed byvan Duin ( 1992;Van Duin et al., 1992)was used.at 9 lcatins thrughutthelakesedimentatin fluxes were measured at tw-weekly intervals,using cylindrical sediment traps with an internal diameterf 6cm and a lengthf 60cm. In the material cllected with the traps the cncentratin fsediment fractins was als measured. At a numberf statins arund thelakethe waterlevelwasbserved twice aday. T measure thecncentratin f sediment fractins inthe bttm sediment bx-cre samples were taken.sub-samples weretaken usingcylinderswithaninternal diameterf12.4 cmand a heightf 40 cm. These were used in resuspensin/ersin experiments, using a simple experimental setup described bytsai and Lick (1986). Results Mdel calibratin Using a wind drag cefficient f (dimensinless) and a Manning cefficient f (m 1/3 s" 1 ) a reasnable recnstructin f the water level variatin is btained. Sme results are shwn in Figure Waterlevel (m) 0.25 cmputed waterlevel bservedwaterlevel ra K i J h u 1 y»y ] WA V ! 1 i Jan Feb Mar Time (mnths) Fig Observed and simulated water level variatin atlcatin Hutrib sluice. 135

94 CHAPTER 8 B ^ -V-\ Sedimentaccumulatin rate (m/year) < t/m 0.10 _ i 0.00 t/m 0.01 g > t/m t/m 0.04 Fig.8.6. Simulatin grwth f the sediment layer (m year 1 ) in 4 perids. 138

95 MODELLING DIAGENESIS OF AQUATIC SEDIMENTS AND DISPERSION OF CONTAMINANTS IN LAKE IJSSELMEER Table 8.4. Observed and simulated net sedimentatin (cm year 1 ) in deep pits and channels inlake IJsselmeer and in general inlake Ketelmeer Lake Ketelmeer Y, Y 2 Y Tabel8.5. Lead cntentf the slids supplied by theriver IJssel (partly prgnstic). Perid Pb-cntent (mg kg 1 ) Basednthe sediment transprt simulatinresultsthespatialdistributin andtempralvariatinf thelead cncentratin in LakeIJsselmeer was simulated. InTable 8.5 thepbcntentf the slids suppliedbytheriver IJssel, used asan inputvariable,is presented. Figure 8.7 shwsthe simulated Pb cntent at seven characteristic dates fr the upper 5 cm f the sediments. In this discussin we fcus n results f the simulatin fr the deep channel in the centre f the present Lake IJsselmeer; a majr sedimentatin area. These results shw a gradual decrease in the Pb-cntent in the perid frm 1957 till The simulated cntaminant cncentratin in thefrmer tidalchannel in 1979 (Fig.8.7a D)is higher thanin 1970, despitethefact thatthepbladsbytheriverijssel aredecreasing andthedilutin byinternally prduced CaC0 3 isincreasing. Duet thecnstructin f theplder Suthern Flevland and later the dike separating Lake Markermeer frm Lake IJsselmeer the internal redistributin f sediments, with alwer Pbcntent than the slids supplied by theriverijssel,wasblcked. Hwever, after this perid the Pb-cntent is decreasing again (results are shwn fr 1987, 1997 and 2005 in Fig. 8.7b), due tthe decreasing cntaminant ladsby theriverijssel. Simulatinresultsarecmpared withbserved changesinthe Pb-cntentinsedimentcresinLake Ketelmeerand Lake IJsselmeerinTable8.6.Atallsites thebservedcncentratinsand tempralvariatin isrecnstructed quitewell. In rder t simulate the effects f dredging the cntaminated sediment layer in Lake Ketelmeer a simulatin wasdne fr a situatin in which thecntaminant cntent in Lake Ketelmeer was reduced tnly 10 (mg kg 1 ) in Results (Fig.8.7b H)shwthat the decreasef Pb cncentratins inlake 139

96 CHAPTER 8 Table 8.6. Observed and simulated Pb-cntents f depsited sediments (mg kg 1 ) at 4 sites in deep pits r channels in Lake IJsselmeer area invarius years (bserved data based nwinkels andvink (1991) and Beurskens et al. (1993)). K* Y,* Y 2 * Y 3 * * Sites K, Y Y 2 and Y 3 canbe fund in Fig IJsselmeerisfaster thaninsimulatins with the riginalcntaminant cncentratins in LakeKetelmeer (Fig. 8.7b G). Discussinsand cnclusins Themdelling apprach usedinthis study seems t prduce satisfactry results.themdel STRESS- 2d gives areasnable recnstructin f resuspensin, ersin, sedimentatin and hrizntal sediment transprt prcesses, resulting in gd simulatin results fr the ttal suspended slids cncentratin and reasnable results fr the variatin in the sedimentatin fluxes. The latter were smewhat underestimated atsite Z t. Thisis partlyduet thefact thatstress-2d desntaccuntfr the internal prductin f CaC0 3 and rganic matter. Lngtermsedimentatin patternswere btainedby simulatingthesedimenttransprt dynamics fr the perid f ne year fllwed by integratin f these results in time and space and extraplatin f theresults fr a perid f adecade r mre. These results areused inthe mdel DIASPORA t simulatethechanges inmrphlgy and Pb-cntent. InDIASPORA theeffects f internal CaC0 3 prductin and cnslidatin f sediment layers is accunted fr. DIASPORA recnstructs the spatial and tempral variatin in the net sedimentatin fluxes and the grwth f the sediment layer in sedimentatin areasquite well. Using DIASPORA andinfrmatin n the changesin the cntaminant cntentin the slids supplied by the riverijssel resulted in a gd recnstructin f the Pb cntent in sediment cres in Lake IJsselmeer. The simulated spatial variatin in the Pb-cncentratins fits well n the bserved cncentratins in 1978and 1986,discussed inchapter 3 (Figs.3.3 and 3.2). Simulatinresults shw a decreasingpb-cncentratin insedimentatin areasin LakeIJsselmeerin the perid frm 1957till 1970.The results reflect the decline in the Pb-cntent f the slids supplied by the riverijssel in this perid and alsthe increasing CaC0 3 prductin. In %f the simulated sediment accumulatin isattributed t internal CaC0 3 prductin.the decreaseinthe Pbcntent in the sedimentatin areasin Lake IJsselmeer ishwever dminated by theeffects f internal redistributin f sediments in the area. Especially in the suthern part f the lake much sediment is erded, which leads t dilutin f cntaminated slids. This becmes clear when the simulatin results fr 1979, sme years after cnstructin f the plder Suthern Flevland, are analyzed. The cnstructin f theplder and laterthedam separating LakeMarkermeer frm LakeIJsselmeer discnnected Lake IJsselmeer frm the (frmer) ersin areasin the suth.thedecreased dilutinresulted in a temprary increase f the Pb cncentratin in the large sedimentatin areas in Lake IJsselmeer. This despite the decreasing Pb-cntent in the slids supplied by the river IJssel and the increasing dilutin by CaC

97 MODELLING DIAGENESIS OF AQUATIC SEDIMENTS AND DISPERSION OF CONTAMINANTS IN LAKE IJSSELMEER B 1960 Cntentsinmg/kg 0 t/m t/m t/m t/m t/m 60 > t/m 80 Fig.8.7a. SimulatinPb-cncentratinintheupper 5 cmatvariusmments (A-D). 141

98 CHAPTER 8 F 1997 Cntentsinmg/kg 0 t/m t/m 100 : 20 t/m t/m t/m 60 > t/m 80 Fig. 8.7b. Simulatin Pb-cncentratin intheupper 5cm at variusmments (E-G). Simulatin resultsfr ascenariin which Lake Ketelmeer isdredged in 1992are included (H). 142

99 MODELLING DIAGENESIS OF AQUATIC SEDIMENTS AND DISPERSION OF CONTAMINANTS IN LAKE IJSSELMEER prductin. After 1980hwever the Pb cncentratins decreased, due tthe cntinued decline in the ladsby the river IJssel. These simulatin results supprt the cnclusin fwinkels et al, (1997;in prep.; Chapter 7)that the tempral and spatial variability in thecntaminant cncentratins inthelake IJsselmeer areais primarily related t internal redistributin fld depsits inthe IJsselmeer area and dilutin by internally prduced CaC0 3. The mdels STRESS-2d and DIASPORA prvide ausefull instrument t simulatetheeffects f a reductin f thecntaminant lads r dredging f lake areas nthecntaminant distributin within Lake IJsselmeer. The mdel can beadapted frther cntaminants than Pb,which wasused as a prttypeinthis study.t imprvethe desciptin f theeffects falgalgrwth and tsimulate the distributin fnutrients DIASPORA shuld be integrated with a eutrphicatin mdel. Acknwledgements ThisstudywassupprtedbyRijkswaterstaat, DirectrateIJsselmeerareaand Rijkswaterstaat, Institute fr Inland WaterManagement and WasteWater Treatment. We thankprf.dr. L. Lijklema (Wageningen Agricultural University, Dept. f Water Quality Management) and Prf. dr. S.B. Krnenberg (Delft Technical University, Faculty ftechnical Earth Science) frtheir critical cmments andsuggestins.we als thank C.L.M. van deven,n.j. Klaver, Y. Bruinsma andr.bertje frtheir cntributins tmdeldevelpment and simulatins. 143

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105 REFERENCES Van Lexmnd, Th.M. and Th. Edelman Preliminary reference values and actual backgrund cntents fr several heavy metals and arsenic in the tp sil f nature reserves and agricultural lands (in Dutch). Research Rep. N , Agricultural University Wageningen,The Netherlands. VanZest, R.and G.T.M.VanEck Behaviur f particulate plychrinated biphenyls andplycyclic armatic hydrcarbnsinthe Scheldt estuary. J. f Sea Res.26: Verhagen,J.H.G Asimulatin mdelfr sediment transprtin Lake IJsselmeer; IJSLIB (indutch). Research Rep. N. 88, Agricultural University Wageningen, The Netherlands. Vieira,S.R., J.L.Hatfield, D.R.Nielsen,andJ.W. Biggar Gestatistical thery andapplicatin tvariability fsme agrnmical prperties. Hilgardia 51: Vink, J.RM. and H.J. Winkels, 1991.Cmpsitin and pllutin status f water depsited sediments f Lake IJsselmeer (in Dutch). Rijkswaterstaat, Flevbericht 326,Lelystad. Vink, J.FM. and H.J.Winkels, In-situ cnslidatin f lake depsits;anempirical mdel trecnstruct pllutin histry. Wat. Res. Bull. 30: Vink, J.RM. and H.J. Winkels, 1996.Cmpsitin and pllutin status f sediments in brder lakes f Flevland (in Dutch). Rijkswaterstaat, Internal reprt nr U, Lelystad. Wakeham, S.G., C. Schaffner and W Giger Plycyclic armatic hydrcarbns in recent lake sediments I. Cmpunds having anthrpgenic rigins. Gechim. Csmchim. Acta 44: Warrick, A.W.and D.E. Myers Optimizatin f sampling lcatins fr varigram calculatins. Water Resurces Res. 23: Webster, R Quantitative spatial analysisf silinthefield, la Advances in sil science 3 (ed. B.A.Stewart) SpringerVerlag,New Yrk, p Webster, R. and M.A. Oliver Statistical Methds in Sil and Land Resurce Survey. Oxfrd University Press,New Yrk, 316 pp. Webster, R. and M.A.Oliver Sample adequately testimate varigramsf sil prperties. /. Sil Science 43: Wehrens, R., P.van Hf, L. Buydens, G. Kateman, M. Vssen, W.H.Mulder and T.Bakker Sampling f aquatic sediments.design f decisin-supprt system and a case study. Analytica Chemica Acta 271: Winkels, H.J Pllutin status f sediments in Lake Markermeer (in Dutch). Internal reprt nr ILi, Rijkswaterstaat, Directrate Flevland, Lelystad, The Netherlands. Winkels, H.J. and A. Stein Optimal cst-effective sampling fr mnitring and dredging f cntaminated sediments. J. Envirn. Qual 26: Winkels, H.J. and A. van Diem Cmpsitin and pllutin status f aquatic sediments in Lake Ketelmeer (in Dutch). Flevbericht 325,Rijkswaterstaat, Directrate Flevland, Lelystad, The Netherlands. Winkels, HJ., A. van Diem and J. Driebergen Extent and degree f pllutin f the sediment in the Ketellake. In Prc. Sixth Int. Cngr. Int. Assc, f Engin. Gelgy (ed.d.g. Price),Balkema, Rtterdam, pp Winkels, HJ., G.Blm, S.B. Krnenberg and L. Lijklema (in prep.). Dilutin f riverineheavy metal inputby resuspensin and algal grwth inlakeijsselmeer, The Netherlands. Submitted twater Research. Winkels, HJ.,J.P.M.Vink, J.E.M.BeurskensandS.B. Krnenberg Distributin andgechrnlgy f priritypllutants in alarge sedimentatin area,riverrhine, The Netherlands. Appl. Gechem. Suppl. Issue2: Winkels, HJ., G. Marin, A.vander Scheer and G.vanMunster Gechrnlgy anddegreef pllutin fpririty pllutants in sedimentatin znes f the Danube delta. Internal RBA-reprt nr LIO,Rijkswaterstaat, directrate Flevland, Lelystad, The Netherlands. Winkels, HJ., O.V Tarussva, M.Y. Lychagin, G.V.Rusakv, N.S.Kasimv, S.B. Krnenberg, G. Marin and G. van Munster Gechrnlgy f pririty pllutants in sedimentatin znes f thevlga delta, incmparisn withtherhine and Danube delta. RIZA-reprt nr , Rijkswaterstaat, Institute fr Inland Water Management and Waste Water Treatment,The Netherlands. Znneveld, P Brabantse Biesbsch (in Dutch), Reprt Stichting Bdemkartering 4,Wageningen, The Netherlands. Zwlsman, J.J.G Immbilizatin fcntaminants inenvirnmental samples; part 4Micrbial degradatin and srptinf rganic pllutants. WL Reprt n. T737, Delft Hydraulics,Delft, The Netherlands. 150

106 Samenvatting De waterbdems in sedimentatiegebieden van grte rivieren kunnen beschuwd wrden als verntreinigde pslagplekken. Het sedimentatiegebied Ketelmeer/IJsselmeer is een dergelijke belangrijke pslagplaats van verntreinigingen van de rivier de Rijn (fwel de IJssel). Recente en histrische verntreinigingen den hun invled hier gelden. De herverdeling van gesuspendeerde stffen en van reeds afgezet sediment als gevlg van ersie (via dr wind geïnduceerde glfwerking) in de ndiepe Nederlandse meren, zal de verntreinigingsniveau's van deze sedimenten in die meren beïnvleden. Het del van dit nderzek was de variabiliteit van de verntreiniging in de waterbdems van het Ketelmeer en IJsselmeer te bestuderen en te verklaren met als del het gedrag en het lt van deze verntreinigingen vr de tekmst te vrspellen. Hiervr zijn diverse methden en mdellen ntwikkeld f aangepast. Hfdstuk 2beschrijft het bemnsteren, de analyse en de interpretatie van de verkregen resultaten vrbrkernen, tplaag mnsters en gelgisch verschillende sedimentlagen uit de waterbdem van het Ketelmeer. Debrkernen uithet Ketelmeer zijn in laagjes verdeeld enelklaagje isgedateerd met behulp vanradichemische technieken (cesium-istpen), zdat het afzettingstijdstip uit het verleden van elk laagje achterhaald werd. Elk laagje werd tevens geanalyseerd p het vrkmen van metalen en rganische verntreinigingen. Dr de cncentraties van deze verntreinigingen per laagje uit te zettentegen hetafzettingstijdstip ishetmgelijk deverntreinigingsgeschiedenis drde rivier de IJssel te achterhalen. Deaangetrffen cncentratie veranderingen met de diepte en dus in detijd werden k waargenmen in de kernen die waren gestken in zandwinputten (plekken met dikke pakketten jng sediment, waar zand was gewnnen bij de aanleg van de plderdijken) in het Ketelmeer. Opmerkelijk waren kdeverschillen inverntreinigingsniveau tussen de tplaag van sediment uitde recente IJsselmeer Afzettingen (IJm-afzetting) en die van de gehele laag van deze afzettingen in het Ketelmeer. De hiernder aangetrffen, udere Zuiderzee Afzettingen (Zu-afzetting) hebben natuurlijke, lage gehaltes aan metalen, plycyclische armatische klwaterstffen (PAK's) en plychlrbiphenylen (PCBs).Hieruit valtafteleiden,dat het verticale transprt vandezeverntreinigingen met infiltrerend water verwaarlsbaar is in dit meer. De metaal- en PAK's-cncentraties in de IJmafzetting uit de brkernen geven een ged beeld van de histrische belasting dr de rivier de IJssel gedurende de laatste vijftig jaar.dezehistrische belasting ziet er als vlgtuit: lage cncentraties aan metalen en iets verhgde cncentraties aan PAK's in het begin van de jaren veertig; een mgelijke verlagingvandeze gehaltengedurendede TweedeWereldrlg en de hgste cncentraties vandeze stffen gedurende deperide Recent afgezette sedimenten hebben (pnieuw)relatief lage gehalten, waarbij vr smmige stffen (ld, arseen en alle PAK's) geldt, dat de gehalten hiervan zelfs de laagste zijn die it werden aangetrffen gedurende de laatste vijf decades. Bijna alle gechlreerde cmpnenten vertnen een afname in cncentratie rnd het begin van de jaren zeventig indeanaerbesedimenten vanhet Ketelmeer, alszewrden vergeleken met udetplaagmnsters uit 1972,die waren bewaard en alsng zijn geanalyseerd. Vrdiverse PCB's is een significante afname in decncentratie vastgesteld, welke het gevlg kan zijn vaneen anaerbemicrbiëledechlrering in hetsediment. Hierdrzijn decncentratieprfielen vandeze gechlreerdecmpnenten geen directe 151

107 SAMENVATTING afspiegeling van de rginele histrische belasting dr de rivier.ondanks de afname van de cncentratie van PCB's zijn tch de navlgende trends herkenbaar in de cncentratieprfielen uit het Ketelmeersediment: - De brkernen hebben lage cncentraties vr alle bestudeerde PCB's in het begin van de jaren veertig. - Dehgste gehalten wrden aangetrffen in deperide De recente sedimenten bevatten ng steeds verhgde gehalten in vergelijking met het begin van de jaren veertig. Algemeen kan gecncludeerd wrden, dat recent afgezet sediment in het Ketelmeer duidelijk lagere gehaltes aan verntreinigingen bevat dan sediment dat isafgezet in deperide Hiermee is duidelijk datindit meerzwaarverntreinigde sedimenten mmenteel wrden afgedekt meteen laagje minder verntreinigd sediment. Desalniettemin zullen erplekken inhet Ketelmeer zijn, zals ersieve deelgebieden en gebieden waar vaargeul nderhud werd uitgeverd, waar deze sterk verntreinigde sedimenten uitde jaren zestigenzeventig aan hetwaterppervlak liggenendaardeaquatischebdemfauna negatief beïnvleden via het benthischevedselweb. In Hfdstuk 3isaandacht besteed aande verspreiding vandeverntreinigingen (inhethrizntale vlak,hetvertikale vlakenindetijd) indewaterbdems vanhet KetelmeerenhetIJsselmeer. Hiervr werden de cncentraties aanmetalen, PAK's, PCB's endiverse sedimentkarakteristieken bepaald in77 tplaag sedimentmnsters en twee (3 meter lange) brkernen uit beide meren. Om de ernst van de verntreiniging te kunnen schatten werdendegeanalyseerde, absluteverntreinigingsgehalten p het lutum- en rganische stf-gehalte van elk individueel sedimentmnster genrmaliseerd. Hiermee wrdtvergelijking van de matevanverntreiniging vrzandigeen slibrijke sedimentmnsters (diein deze meren vrkmen) mgelijk. In 25%van het IJsselmeer wrdt de jngste gelgische laag (de IJm-afzetting) aangetrffen; dit betreft de diepe delen (de nett sedimentatiegebieden) van dit meer. Deze IJm-afzetting is in het Ketelmeer ernstig verntreinigd (zie k Hfdstuk 2). De gehaltes aan bvengenemde verntreinigende stffen zijn echter in de IJm-afzetting in het IJsselmeer een factr 1,6 tt 9lagerdanin dezelfde afzetting inhet Ketelmeer. In de verige 75% van het IJsselmeer liggen vrnamelijk udere,zandige afzettingen aan het ppervlak, die een factr 2tt 4 lagere gehalten aan verntreinigende stffen hebben dan de IJm-afzetting uit dit meer. Uitbeide brkernen valt af te leiden,dat degehaltenaanmetalen, arseenen PCB's indeijm-afzetting eersttenemen metdediepteen later weerafnemen (sms tt nder de detectie grens).deze trend kmt vereen met de geschiedenis van debelasting met verntreinigingen dr de rivierdeijssel gedurende de laatste 5decades. Als de brkernen uit de IJm-afzetting in beide meren wrden vergeleken blijkt de verntreinigingsgraad af te nemen met een tenemende afstand tt de IJsselmnding. De hypthese is ntwikkeld dat verdunningin hetijsselmeer tt standkmt dr zwelbijmenging met geërdeerd sediment uitditmeer als drkalkprecipitatie ten gevlgvanprimaire prductie. In Hfdstuk 4 wrdt de verwerking en de interpretatie van brkernen uit vergelijkbare sedimentatiegebieden vantweegrte rivierdelta'sbeschreven. Opunifrme wijze zijn hiervr indewlgaen Dnau delta's anaerbe slibrijke sedimenten bemnsterd, waarbij gebruik is gemaakt van satelietbeelden, welke de zwevende stfgehaltes in het water weergeven. Via de datering van bemnsterde laagjes (metbehulp van cesium-istpen) en drhet meten van decncentraties van metalen, PAK's en PCB's hierin,zijn cncentratieprfielen afgeleid welkevrmetalen en PAK'sde histrische belasting p deze rivieren weergeven. De gehaltes van de bestudeerde 7 PCB's en van cadmium waren in alle sedimentmnsters uit beide delta's zdanig laag, dat de detectie grens niet werd verschreden. Lage en nageneg niet veranderende cncentraties aan arseen, kper, zink en alle bestudeerde PAK's werden waargenmen in sedimenten uit dewlgadelta, diewaren afgezet gedurende delaatste vijftig jaar. Verderwaren decncentraties aan nikkel ietsverhgd en bevatten de meest recente sedimenten 152

108 SAMENVATTING uit deze delta enigszinds stijgende gehalten aan zink,chrm en arseen. Dehistrische belasting vr de Dnau delta ziet er vr metalen en PAK's als vlgt uit: lage cncentraties metalen en verhgde cncentraties aan PAK's inhetbegin van de jaren veertig;tenemende gehaltesvr deze stfgrepen in deperide en afnemende gehaltes na laatstgenemde peride in derecente sedimenten. Bij vergelijking van de verntreinigingsgraad (metalen, PAK's en PCB's) van de sedimenten uit de delta'svanwlga, Dnau enrijn,blijkt de Wlga deltanu enin het recente verleden de schnstevan dedrie tezijn. Deaangetrffen verschillen inverntreinigingsgraad gedurende delaatstevijftig jaarin deze drie delta'skunnenverklaard wrdendr (i) eenverschil in natuurlijke achtergrndgehalten vr de rivieren; (ii) een verschillende intensiteit van industriële activiteiten en daarmee gepaard gaande belastingvan de rivieren en (iii)eenverschillend beheerindestrmgebieden van de rivieren (bijvrbeeld dr aanleg stuwmeren). De thans afgezette sedimenten in derijn deltabevatten ng steeds de hgste gehalten aan metalen (behalve kper en nikkel), PAK's en PCB's in vergelijking met beide andere delta's, maar het belastingsniveau dr de industrie p deze rivieren is vr de Dnau inmiddelshethgst vrde meeste zware metalen. In Hfdstuk 5 wrdt een vr het Ketelmeer gekzen gestatistische bemnsteringsaanpak vr sedimenten uitgelegd. Als verntreinigingsgehalten en daaraan gerelateerde sediment karakteristieken wrden gevlgd in de tijd in een aquatisch milieu, dient rekening te wrden gehuden met de ruimtelijke variabiliteitvan deze grtheden.de hiergekzenbemnsteringsstrategie vr sedimenten dientdan kdevariabiliteit vandezevariabelen pzwel krte (65m) alslangere afstand (500m)te verdiscnteren. In het Ketelmeer werden drie deelgebieden vr nderzek gekzen, waarbij de grttevandeze gebieden mede bepalend wasvrbvengenemde afstanden tussen de verschillende bemnsteringspunten. De drie deelgebieden zijn vraf gekzen p basis van verschillen in waterdiepte,verschillen in sedimentatie/erssie gedrag en p basis van verschillen in sediment type (kleif zand). Vr het mnitren van verntreinigingstrends in sedimenten kan via deze bemnsteringsstrategie het aantal mnsterpunten wrden geminimaliseerd, afhankelijk van de nauwkeurigheid waarmee de verntreinigingsgraad dient te wrden vastgesteld. De keuze vreen dergelijke bemnsteringsstrategie m verntreinigingstrends insedimenten te mnitren zalvrelkdeelgebied kunnen leiden tt een andere afstand tussen de mnsterpunten. In het centrale deel van het Ketelmeer wrdt bijvrbeeld een ptimale bemnsteringsafstand vr het mnitren van de gehalten aan Benz(A)pyrene (BAP) gevnden, die grter is (minder punten per vierkante kilmeter) dan in het zuidelijke deelnabij Ketelhaven,waardegradiënten inwaterdiepte grter zijn. Opvergelijkbare wijze werd k gevnden, dat vr het saneren (afgraven) van de verntreinigde laag in het Ketelmeer een p bvenstaande gebaseerdekeuze vandezedeelgebieden in een saneringsbestek ndzakelijk is, m het nauwkeurig verwijderen van deze laag te kunnen garanderen. Als geen rekening wrdt gehuden met de ruimtelijke variabiliteitvan de diktevande verntreinigde laag isde kans grtdatsterk verntreinigde putgebieden nvlledig f niet en gedeeltelijk schne sedimenten wel wrden afgegraven. Daarm wrdt aanbevlen vrafgaand aan de sanering nauwkeurig (hewel kstbaar) ruimtelijk nderzeknaar de diktevandeverntreinigde laagpervraf geïdentificeerd deelgebied uit teveren. Vr het mnitren van verntreinigingstrends zijn pragmatische, gestatistische methden beschikbaar die,afhankelijk van de gewenste nauwkeurigheid, debemnsteringsksten kunnen beperken. Eenander belangrijk prces,dat de cncentratieprfielen insedimenten beïnvledt,is cnslidatie. Hfdstuk 6 behandeld dit fysische prces waarbij zwevende stf sedimenteert en na afzetting water verliest. In principe is het mgelijk (en vaak gedaan) m dit cnslidatieprces met mathematische mdellente beschrijven, maarvanwege despecifieke mstandigheden in het IJsselmeergebied leek een empirische aanpak beter. Vijf representatieve kernen van de IJm-afzetting in diepe sedimentatiegebieden werden, verspreid ver het IJsselmeergebied gestken. Daarnaast waren peridieke diepteldingen beschikbaar p deze vijf plekken gedurende de laatste zestig jaar. Dit verschafte infrmatie 153

109 SAMENVATTING met betrekking tt de ttale dikte van dezeijm-afzetting en de nett sedimentatiesnelheid gedurende bepaalde perides.omeen equivalent van dediepte vr detijdsas tekunnen achterhalen zijn crrectiefactren ndzakelijk vr de mate van cnslidatie in het sediment. Deze crrectiefactren zijn gebaseerd p de verschillende stadia van cmpressie van het sediment (0%, 30% en 45%). Hiervr werdeenfactr n vr elk bemnsterd laagjeafgeleid, die de verschillendewatergehaltesweergeeft als afhankelijke van hetaanwezige lutumgehalte.viadeze «-factr washetmgelijk de initiële, ngecnslideerde dikte van elk laagje via een mrekening terug te rekenen. Dr deze prcedure werd het mgelijk eenredelijke betruwbare tijdsas m.b.t.dediepteterecnstrueren. Vergelijking met datering drcesium-istpen vreen aantalkernen tndegede vereenstemming. De jaarlijkse variabiliteit aanverntreinigende stffen inhetijsselmeergebied wrdt beschreven in Hfdstuk 7. Frequente metingen van gehaltes van zeszwaremetalen inde zwevende stf in deijssel eninhetbezinkend slib p twee plekken in hetijsselmeergaveneen kenmerkenderuimtelijke gradiënt tezien.degehaltesaan zware metalen namen gedurende hethele jaar afmeteen tenemende afstand vanaf de IJsselmnding. Deze ruimtelijke gradiënt kmt vereen met de gradiënt die k werd aangetrffen in de afgezette sedimenten in dit gebied (Hfdstuk 3).Metingen in brkernen uit het Ketelmeer (nabij de IJsselmnding) en uit het centrale, diepere deel van het IJsselmeer laten zien, dat de gehaltes aan zware metalen in de gelijktijdig afgezette sedimenten van het Ketelmeer 2 tt 3 keer hger zijn dan inhet IJsselmeer. Bvengenemde cncentratiegradiënt inhetbezinkend slibblijft k significant als de gehalten aan zware metalen wrden genrmaliseerd m.b.t. het lutum- en rganische stf-gehalte van elk individueel bezinkend slibmnster. Op basis van een ruwe sedimentbalans vr deze zware metalen, gebaseerd p aanvergegevens van de rivier en p de gemeten sedimentatie fluxen, wrdtduidelijk datde ttaleinternefluxen vanzwaremetaleninhetijsselmeerveelgrter zijn dan de externe aanver dr de rivier de IJssel. Naast zware metalen zijn k diverse sedimentkarakteristieken en een aantal variabelen die verband huden met primaire prduktie gedurende een jaar gemetenin het bezinkendslib enin het water p tweelkatiesin het IJsselmeer.Via enkelvudigecrrelaties is getracht het gedrag van de zware metalen in de tijd en de gevnden ruimtelijke gradiënt te verklaren,maar de cmplexiteitvande relatiestussende zwaremetalenendevariabelen dieeenindruk geven van primaire prduktie en/f ersie stnd dit niet te. Dr tepassing van statistische techniekenzals factr analyse (PCA) enstapsgewijs,meervudigcrrelatienderzek (SMR) werd echter duidelijk dat de variatie van de cncentratie van zware metalen in bezinkend slibin het zuidelijk deel van het IJsselmeer een verband tnt met de windsnelheid ter plekke en met het lutumgehalte (beide variabelen wrdenbeïnvleddr resuspensievansediment),terwijl zein het centraledeelvan het IJsselmeer gerelateerd zijn aan de ph, hetchlrphyll-en het kalkgehalte (dezevariabelen wrden beïnvled dr de jaarlijks ptredende algenbleien). De negatieve crrelatie tussen de meeste zware metalen in het bezinkend slib en het chlrphyll gehalte en het rganische stfgehalte in het water rechtvaardigt de cnclusie, dat in het centrale deel van het IJsselmeer, waar de algen cncentraties in de zmer hg zijn, een verdunning ptreedt van de verntreinigde zwevende stfdeeltjes als gevlg van primaire prduktie. In het zuidelijk deel van het IJsselmeer duidt de psitieve crrelatie van de meestezwaremetaleninhet bezinkend slibenvan hetlutumgehaltemetde windsnelheid terplekkep resuspensie van recent afgezette sedimenten als verklaring vr de variatie in de gehalten zware metalen in de zwevende stf in het water. De geleidelijke tename van de ó 13 C-waarde vanaf de IJsselmnd via het zuidelijke deel van het IJsselmeer tt het centrale deel van het IJsselmeer duidt er p dat zet water sedimenten in dit gebied wrden gemengd met geërdeerde Zu-afzettingen, dievan rsprng marien (zut) zijn. Opbasis van dit nderzek kan derhalve gecncludeerd wrden, dat de afname van de gehaltesaan zware metalenin de zwevendestf en in de waterbdemvan hetijsselmeer ntstaat dr een verdunning van deze verntreiniging dr ersie van udere sedimenten en dr primaire prduktie gerelateerd aan algenblei. 154

110 SAMENVATTING In Hfdstuk 8 wrdt de pgedane kennis betreffende de verntreinigde sedimenten, de verdunning, hettransprtenprcessen zals cnslidatieen primaire prduktie,welke ptreden indit nderzeksgebied, samengebracht in een mdel kader. Daarbij werd een recnstruktie van de sediment transprtprcessen en dedaaraan gerelateerde verdunning van deverntreiniging inhet IJsselmeergebied gemaaktvr enkele decades. Deze excercitievrmde de basis vr eenschattingvande tekmstige sedimentsamenstelling en verntreinigingsgraad, welke afhankelijk van de verwachte belasting drde rivier deijsselwerd gemdelleerd. Het aangepaste mdel STRESS-2d recnstrueert de resuspensie, de ersie, de sedimentatie en de hrizntale sediment transprtprcessen gedurende een jaar. De gesimuleerde resultaten hiervan kwamen ged vereen met de gemeten ttale zwevende stf cncentraties en de sedimentatie fluxen in het IJsselmeer. Het mdel is vervlgens genest in het nieuw ntwikkelde mdel DIASPORA, dat de mrflgische veranderingen t.g.v. nett sedimentatie fluxen pdelangeretermijn ged simuleert. DIASPORA hudthierbij rekening metdeeffecten vanbigene kalkprecipitatie en de cnslidatie van het sediment na afzetting. De afname van de ldcncentratie in de sedimentatiegebieden in het IJsselmeer kmt vereen met de gereduceerde input van ld in de drde IJssel aangeverde zwevendestf,maarwrdtgedmineerd drdeeffecten dieinterne transprt prcessen van sedimenten in het gebied hierp hebben. De mdelresultaten bevestigen dan k bvengenemde sltcnclusie uithfdstuk 7. Simulatie vandesedimentatiefluxen en vrspellingen vrde gehaltesaanldindewaterbdemwerdenuitgeverd vreencnstante sedimentaanver en vreen 50%reductie van de ldaanver dr de IJssel.Deresultaten laten een vrtgaande daling van de ldgehaltes in de sedimentatiegebieden van het IJsselmeer zien en een extra zuiveringseffect alsgevlg van de sanering (afgraving) vanverntreinigde sedimenten inhet Ketelmeer. 155

111 Dankwrd Alseerstegaat mijn dank uitnaarmijn beideprmtren SalleKrnenberg enbertlijklema. Vral vrhet vertruwen dat menin mij alsnderzeker steldeenvrdevrijheid die menmij vervlgens gaf bij de invulling en uitvering van het nderzek. Daarnaast leverde men dr het cmmentaar p dediversemanuscripten een waardevlle bijdrage. Dit vertruwen was niet alleen beperkt tt mijn beide prmtren k binnen Rijkswaterstaat, RIZAhebben metnamebartfkkensenalbert dehaashetmgelijk gemaakt, dat ikditnderzekswerk kn uitveren en afrnden. Jullie persnlijke betrkkenheid werd erg p prijs gesteld en k jullie creatieve interpretatie van begrippen als "deadline en fasering in de tijd" zrgden ervr dat de Prdukten uit dit prject gelukkignit te laat waren.ok wil ik Henk Bs bedanken die met mijvr defraaie vrmgeving vanditprefschrift zrg dreg. Onderzek de je peen nderzeksafdeling enbij mijn eigen taakveld heb ikdaarvr de ruimte en de assistentie gekregen van velen. Hiervr ben ik iedereen dankbaar. In het bijznder wil ik Js Vink danken vr nze vruchtbare discussies ver de inhud en de uitwerking van bepaalde nderzeksresultaten. Jebent vrmij een vrbeeld van eenexcellente prmvendus geweest. Om een slibmdel te buwen en er vr te zrgen dat alles k ng werkt is specifieke kennis vereist, die ik niet bezat. Gerard Blm, Nic Klaver, Yde Bruinsma en Kees van de Ven hebben hun specifieke kennis ingezet m deze prmtie te den slagen. In de werkgrep WIJS (werkgrep IJsselmeerslib) was deze kennis p unieke wijze gebundeld. Hewel niet altijd alles vlgens de prjectplanning verliep en "de laatste ldjes" zwaar waren, is er inhudelijk zeer ged werk dr jullie geleverd en k ng peen vr mij zeerprettige manier. De leiding en vrmalig medewerkers en cllega's van de hfdafdeling Landinrichting van de Rijksdienst vrde IJsselmeerplders, later Rijkswaterstaat, Directie IJsselmeergebied, wil ik danken vr hunfinanciële en mrelesteun,dieik gedurendehet nderzekvan hen mcht ntvangen. Ik hp dat dit prduktk een "kleine bijdrage"levertaanhet geweldige prduktdat deze hfdafdeling heeft achtergelaten vr "hethart van Nederland". De medewerkers van de afdeling AN van Rijkswaterstaat Directie IJsselmeergebied maakten het mgelijk dat ik veel bemnsteringen van de waterbdem mcht uitveren in pdracht van hen. Ok financieel en inhudelijk is bijgedragen tt de ntwikkeling van het slibmdel. Ik denk hierbij met name aan de bijdragen van Jan Driebergen, Huub Hectr en Wil van de Geer. Ok wil ik de medewerkers die het veldwerk verzrgden nder leiding van Hans Minderhut p de brbten hartelijk danken vrhun inzet. Verderwil ikeen ieder danken die even de tijd nam "metmij mee te denken",want p diewijze wist ikhen zver tekrijgen dat zij mehielpen als ikwasvast gelpen. Mijn uders hebben mij hetbelang van studielateninzienenmijn brersen zussenhebben mij het vrbeeld vanvlhardinginstudie enwerkgetnt (ditis blijkbaar erfelijk). Okdank ik henvr hun belangstelling.mijn schnuders enhetinhetbijznder Mutti dankikvrhun enthusiasme, steun en warmte.mutti, u bent vrmij een vrbeeld vanhehet met. LieveMara,Jessy en Sphievr jullie wasikerhelaasteweinig deafgelpen perideen alsiker wasdanwaren mijn gedachten ng nietaltijd bij jullie.mara, je hadgelijk het is demeitewaardenik ben blij dat ik p juw initiatief ben gestart en dat je me altijd bent blijven ndersteunen. Niet alleen daarm hu ikheelveel van je! Herman 157