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
Interaction Macrophyte biodiversity
Biochemistry O2, nutrients, turbidity, …
Geomorphology
Sedimentation and erosion
Ecological quality
Water quality
Structural quality
1
Part 1: Macrophyte growth and diversity
2
Macrophyte occurrence in the Nete catchment
Macrophyte occurrence in the Nete catchment Seasonal variation
Macrophyte occurrence in the Nete catchment… Zooming in on the Aa subcatchment Yearly variation 350
2006 2005
-2
biomass (g m )
300
2004
250 2003
200 150 100 50 0 1
2
3
4
5
6
7
months
8
9
10
11
12
Macrophyte occurrence in the Nete catchment… Zooming in on the Aa subcatchment Species variation
Biomass (g m-2)
2003 2004 2005
c
120
90
60
b
c 30
b a
b
a a
a
b c
a
a
a a
a a a
a a
b
0 Cplat
Cdeme
Enutt
Pnata
Ssagi
Semer
Spect
Part 2: How do macrophytes shape our rivers?
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Study area: Zwarte Nete
± 4.5 m
Retie
8
Callitriche platycarpa patches, Zwarte Nete, Retie
Zwarte Nete
April
May
June
July
Mowed
August
September
9
Different patch sizes 1 pattern
Power law
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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.
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What are scale-dependent feedbacks?
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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
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Positive effect: sedimentation in patch (theory)
current
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Positive effect: sedimentation in patch (field setup 1)
• •
2013-2014 monthly measurement
Bathymetry is measurend in and around a developping patch
15
Positive effect: sedimentation in patch (results1)
June
Top view
• July
•
August
• •
Width of frame: 250 cm Length of frame: 100cm
Green: sedimentation Red: erosion
September 16
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
Fast current, no erosion. Where is negative feedback?
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But then where is the negative feedback? Field experiment 3: impact of the stream velocity on plants
+
Transplantation experiment with Callitriche platycarpa 2008 and 2009 Initial mass: 25 - 100 g
0 _
Duration: 6 weeks
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Negative feedback
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Part 4: How do macrophytes affect river water quality?
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Experimental setup on the Aa
Upstream gate
Downstream gate
Middel
± 1,5 km
Slootbeek
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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+)
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(MANUDYN I Report)
24
15N
experiments
•
P. natans and C. platycarpa
•
Standard Kilham (1998) nutrient solution
•
15N
NH4 + NO3 addition for 4-6 h
(MANUDYN II Report., 2011)
25
Contribution of different plant traits to N uptake (%)
Shoot uptake more important in nutrient rich water
(MANUDYN II Report, 2011)
26
-1 Total nitrogen balance (kg N dag )
213-550
205-480 1-3
But this is only temporarily storage!!!
(MANUDYN I Report)
27
Impact on biogeochemistry Current
Macro-invertebrates
POM
Sedimentation
Bacteria
Nutrients
28
Patch is hotspot for organic matter accumulation
8-month period field measurements
Eutrophic river Oligotrophic river 29
Increasing organic matter with increasing biomass
Patches are hotspots for organic matter accumulation
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Permanent nitrogen removal
31
Underlying mechanisms are interactions between hydraulics, vegetation, nutrient availability, physical stress by high velocity, and more….
Macrophyte growth stimulated
Macrophyte patch vpatch=low
High nutrient content
High organic carbon High mineralisation High denitrification
Discharge
SS
vfree=high
Sedimentation
Low organic carbon
Free – cascade effects / feedback
32
Part 5: A difficult balance between water management and ecology.
33
Situation in Flanders
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ECOBE archive
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
River Aa: 2003 – 2006: dominance by P. natans
Aa, Poederlee
Example river Aa: 2003 – 2006: 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?
A difficult balance between water management and ecology. Costs
• •
740.000€ per year Ecological cost
40
A difficult balance between water management and ecology. Benefits
• •
Efficient for economy, households, industry, agriculture
1x maaien
2x maaien
30 cm
41
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
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
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
Can we come up with an optimal mowing strategy? Different patterns
full
empty
Flume Flanders Hydraulics, Borgerhout
45
(Bal et al., 2011)
Can we come up with an optimal mowing strategy?
full
empty
Average Manning n for each pattern 0.6
Manning
0.5 0.4
10 times lower
0.3 0.2 0.1 0 1
2
3
4
5
Patroon nummer
46
(Bal et al., 2011)
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
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”.
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• 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
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
