Invloed van waterplanten en maaibeheer op de ecologie en hydrologie van waterlopen

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1 Invloed van waterplanten en maaibeheer op de ecologie en hydrologie van waterlopen Prof. Patrick Meire Dr. Jonas Schoelynck Dr. Kris Bal Ir. Kerst Buis Veerle Verschoren Platform Beek- en Rivierherstel Beheer en Onderhoud Arnhem, April 17, 2014

2 Macrophyte biodiversity Interaction Ecological quality Biochemistry O 2, nutrients, turbidity, Water quality Geomorphology Sedimentation and erosion Structural quality 1

3 Part 1: Macrophyte growth and diversity 2

4 Macrophyte occurrence in the Nete catchment

5 Macrophyte occurrence in the Nete catchment Seasonal variation

6 biomass (g m -2 ) Macrophyte occurrence in the Nete catchment Zooming in on the Aa subcatchment Yearly variation months

7 Biomass (g m -2 ) Macrophyte occurrence in the Nete catchment Zooming in on the Aa subcatchment Species variation c b c b b a a a a b c a a a a b a a a a a Cplat Cdeme Enutt Pnata Ssagi Semer Spect

8 Part 2: How do macrophytes shape our rivers? 7

9 Study area: Zwarte Nete ± 4.5 m Retie 8 Callitriche platycarpa patches, Zwarte Nete, Retie

10 Zwarte Nete April May June July Mowed August September 9

11 Different patch sizes 1 pattern Power law 10

12 Patch size distribution gives rise to a power-law distribution. This is a strong indication for an ecosystem that is self-organised. Scale-dependent feedbacks between organisms and their environment are a necessary condition for self-organisation. 11

13 What are scale-dependent feedbacks? 12

14 Patch formation as a result of scale-dependent feedbacks These are feedbacks between organism and environment which are positive on a short distance from the organism but become negative further away. Negative feedback is erosion next to the patches Positive feedback is sedimentation inside the patches 13

15 Positive effect: sedimentation in patch (theory) current 14

16 Positive effect: sedimentation in patch (field setup 1) monthly measurement Bathymetry is measurend in and around a developping patch 15

17 Positive effect: sedimentation in patch (results1) June July August Top view Width of frame: 250 cm Length of frame: 100cm Green: sedimentation Red: erosion September 16

18 Positive and negtive effect: sedimentation in patch, erosion next to the patch (field setup 2) Faster current (+30%) but is there erosion? Slow current (up to -100%) increased sedimentation 17

19 Fast current, no erosion. Where is negative feedback? 18

20 But then where is the negative feedback? Field experiment 3: impact of the stream velocity on plants 0 _ + Transplantation experiment with Callitriche platycarpa 2008 and 2009 Initial mass: g Duration: 6 weeks 19

21 Negative feedback 20

22 Part 4: How do macrophytes affect river water quality? 21

23 Experimental setup on the Aa Upstream gate Downstream gate Middel ± 1,5 km Slootbeek 22

24 Measurements Stream velocity profile Measurements on water samples (open water & within macrophytes) - Every 2 hours (O2, temperature, ph, conductivity, N-NH4+, N-NO2-, N-NO3-, P-PO43-) - Every 4 hours (BOD, SO42-, Cl-, chlorophyll a, Na+, K+, Ca2+, Mg2+, Fe2+) 23

25 (MANUDYN I Report) 24

26 15 N experiments P. natans and C. platycarpa Standard Kilham (1998) nutrient solution 15 N NH 4 + NO 3 addition for 4-6 h (MANUDYN II Report., 2011) 25

27 Contribution of different plant traits to N uptake (%) Shoot uptake more important in nutrient rich water (MANUDYN II Report, 2011) 26

28 Total nitrogen balance (kg N dag -1 ) But this is only temporarily storage!!! (MANUDYN I Report) 27

29 Impact on biogeochemistry Current Macro-invertebrates POM Sedimentation Bacteria Nutrients 28

30 Patch is hotspot for organic matter accumulation 8-month period field measurements Eutrophic river Oligotrophic river 29

31 Increasing organic matter with increasing biomass Patches are hotspots for organic matter accumulation 30

32 Permanent nitrogen removal 31

33 Underlying mechanisms are interactions between hydraulics, vegetation, nutrient availability, physical stress by high velocity, and more. Macrophyte growth stimulated Discharge v patch=low SS Macrophyte patch High organic carbon High mineralisation Sedimentation High nutrient content High denitrification v free=high Low organic carbon Free cascade effects / feedback 32

34 Part 5: A difficult balance between water management and ecology. 33

35 Situation in Flanders 34 ECOBE archive

36 Situation in Flanders Since 60-ties: deterioration of river quality, mainly by unlimited nutrient input and intensive bank reinforcement Loss of macrophytes Since early 90-ties: implementation of EU Directive on Urban Wastewater: water quality improvement Since late 90-ties: management activities improving structural quality (e.g. re-meandering, fish traps ) Macrophytes make a comeback Since 2000: macrophytes implemented in EU Water Framework Directive But still too many nutrients resulting in large biomass production 35

37 River Aa: : dominance by P. natans Aa, Poederlee

38 Example river Aa: : dominance by P. natans 1. Increased maximum biomass 2. Prolonged growth period Many practical management questions 1. How much vegetation do we remove in order to prevent flooding? 2. When do we have to remove aquatic plants and how often? 3. Why is re-growth so fast?

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41 A difficult balance between water management and ecology. Costs per year Ecological cost 40

42 A difficult balance between water management and ecology. Benefits Efficient for economy, households, industry, agriculture 1x maaien 2x maaien 30 cm 41

43 A difficult balance between water management and ecology. How about sustainability??? Regrowth after a few weeks remowing necessary What about all unknown parameters/effects? 42

44 A difficult balance between water management and ecology. Annelies Boerema et al, 2013 Cost-benefit analysis mowing in the Nete Catchment All possible ESS Division over stakeholders 43

45 A difficult balance between water management and ecology. we conclude that aquatic vegetation removal in the Nete catchment is not economically efficient, costs and benefits are not equally shared and the management technique as applied today is not sustainable Boerema et al. Economic valuation of ecosystem services, a case study for aquatic vegetation removal in the Nete Catchment, Belgium. Ecosystem Services In press Hoe dan wel??? 44

46 Can we come up with an optimal mowing strategy? Different patterns full empty Flume Flanders Hydraulics, Borgerhout 45 (Bal et al., 2011)

47 Manning Can we come up with an optimal mowing strategy? full empty Average Manning n for each pattern times lower Patroon nummer 46 (Bal et al., 2011)

48 Mogelijke oplossingen alternatieve oplossingen? Waarom zijn er zoveel waterplanten en kan dat niet voorkomen komen? (waterzuivering, beschaduwing...) brede en schuine oevers (lokaal bergende capaciteit) maaien wanneer het echt moet objectieve criteria zijn nodig meer onderzoek + verandering in beleid wanneer toch gemaaid wordt, krijgt patroon maaien de voorkeur 47

49 Conclusie Macrofyten dragen in belangrijke mate aan de structuur van waterlopen door patroonvorming via een proces van zelforganisatie Macrofyten spelen een belangrijke rol in het zuiverend vermogen van waterlopen zowel direct, maar vooral indirect door de transfer van water naar bodem te bevorderen. Ze zijn hotspots of biogeochemistry. 48

50 Het beheer van macrofyten leidt tot een maatschappelijke meerkost door het verlies aan ecosysteemdiensten Geoptimaliseerd beheer waarbij een beperkte hoeveelheid macrofyten wordt verwijderd is een goede oplossing Meer inzicht is nodig in de gevolgen van maaibeheer op hergroei en ruimtelijke patronen. 49

51 Onderzoek aan waterplanten bij Ecobe: een geïntegreerde aanpak Individuele plant Nutriëntenuitwisseling (N, P, Si) Sterke (drag, fysiologie...) Patches Effect op bathymeterie (sedimentatie/erosie) Effect op bodemchemie (organisch materiaal) Reach Ruimtelijke verdeling (patch distributie) Opstuwing (manning, maaien) Afbraak van organisch materiaal Nutriëntretentie 50