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ENCORA Theme 6Overview of bio-geomorphology research in theNetherlands and relations to watermanagementM.B. de VriesWL|Delft Hydraulics, University Twente,University of Technology Delft


Biogeomorphology?• Some species influence their environment inorder to improve or maintain habitat area andhabitat quality (ecosystem-engineers).• In our Dutch soft coastal ecosystems physicalmorphological parameters are influenced,such as erodibility and bed composition.• The study of interactions between biologyand morphology we define asbiogeomorphology (BGM).


Is biogeomorphology relevant formanagement?• The interaction of biology and morphology results incharacteristic ecotopes in the coastal zone.– saltmarshes– sea grass beds– sandy or silty beds dominated by specific species such asbenthic algae and burrowing or grazing zoobenthos– banks of reefbuilding benthos• Therefore the resulting ecotopes are sensitive tochanges in physical and biological parameters of anecosystem.


-+algae &bacteriabed strengtherosionratestabilisation+infaunae.g. mudshrimp,lugworm)+-destabilisationchanged(re)suspensionsedimenttransportbedmixingextramixingknown BGMinteractionspellets+trappingbedlevelbedcompositionepibenthos(e.g. mussel)waves¤taddedroughnessVegetatione.g. sea grass


Why do we need BGM research?• Intertidal areas are important habitats for many birdspecies listed in EU Bird and Habitat directives.• Intertidal areas are rich in biomass and BGMinteractions caused by ecosystem-engineers areexpected here.• Analysis and prediction of currents, waves andsediment transport in coastal systems does notinclude BGM interactions, this could be an omissionwhen trying to understand impacts of human inducedphysical and biological changes.• The relation between BGM interactions on intertidalareas and the functioning of the large scale of thewhole water system is unknown (WFD!).


BGM research in NL• Mathematical models are being extended withBGM processes.• Field and lab. data are used to calibrate math.models.• A lot of the progress is the result of joint researchbetween government and research institutes.• Some of the knowledge and tools are being usedfor advise in commercial projects.• An important research issue is the coupling ofBGM from mudflat scale to water system scale.• Involved parties are NIOO, WL|DelftHydraulics, TUD, UT, UofUtrecht, NIOZ, RWS,IMARES (a.o.)


Fieldwork delivers details as basis forparameterizations needed for modellingWadden Sea, september 2006BGM relationships on mudflatco-operation NIOO-NIOZ-WL


Coupling of phys-bio scalesneeds parameterizationsMorphodynamicsstorminesschannels andtidal flats unitsclimate and SLR,whole water systemkm 21000yearwavedriventransportstidal transports.001silt.01interaction.1sandforcing1mpb + bacteria10zoobenthosnoise 100 =nett effectreefsBiologyseagrassmarshes


Ecosystem engineers in the Wadden SeaBenthic algae(~270km 2 )Musselbeds(~30km 2 )


Modeling of BGM processes, Wadden SeaStabilizersdominate onhigher areasDestabilizersdominate onlower areasRelative changes [-] incritical shearstress (left)en erosion rate (right)caused by eco-engineersRelative amount of silt in bed(left) and in the watercolumn(right), during a storm inDecember 1998.Values >1 indicate an increasein sediment amount caused byBGM processes.


Saltmarshes in the Wadden Sea and theDelta-areaArea in Wadden Sea ~100km 2Area in Delta ~100km 2


modeling flow-vegetation interactions3D model structure (Delft3D):Wave sub-model:input: -topography-boundary: water level-vegetationmeasuredtidalwaterlevelvariationvertical plantstructurespatialdistribution


Part I:modeling short-term interactions (1 tide)Simulations: plants have crucial impact on flow and sedimentationExample 2Sedimentation (g/m²) after 1 tidesimulated sedimentationpattern with vegetation10 melevationmapno vegetationvegetationLevee-basinformation


Some numbers on WS scale• Many years averaged, the NL-Wadden Seaimports about 1000 ton fine sediment pertide. Exchange between NS-WS is 20x larger,fluxes internal WS are 200x larger.• Each tide 15.000 ton fine sediment is fixed aspellets by suspension feeding bivalves,comparable to exchange.• Each tide grazing and burrowing benthosconsume a small layer of sediment. Thisamounts to a layer of about 30 cm per year.• Dependent on the specific location,ecosystem-engineers halve or double thefluxes internal WS.


suspended sedimentconcentration [g/m3]temporal variablesDynamic interaction of silt-transport andBGM• Time- and spatial scales of silt transport could bedynamically coupled to biomass of ecosystem-engineers12108642with0biologywithoutbiologyVliestroommpbzoobenthoswindspeed0 50 100 150 200 250 300 350 400time [days]908070605040302010spm N-Sea0


Influence of BGM on WS scale is large andvariableWatersystem Q1 Q2 Q3 Q4 Depth(m NAP)1. Marsdiep +2.5 +2.5 +4.4 +7.4 5.42. Vliestroom -9.0 -16 -6.8 -1.1 2.43. Eierlandse gat -8.2 -12 -6.5 +5.4 3.54 .Borndiep -23 -9.8 -24 -25 2.85. Zoutkamperlaag -34 -18 -28 -40 3.0Stabilised (km 2 ) 414 438 420 397 19.3%Destabilised 1132 1088 1126 1171 52.2%Difference (%) SPMconcentration between BGMand abiotic modelruns


HumaninfluencesNorth sea fine sediment transport1000 tons/tide nett20.000 tons/tidecoastal infrastructuursand miningmussel,oyster,sandmason sedimentatiecockle,ensis,macomabed surfacefoodwebWadden Sea fine sediment transportSF200.000 tons/tideSDFmudflat scale sediment transportlugwormburialerosieMFBRESDDFland-reclamationdeepening,dredging-dumpingshrimp,fish,birds(shrimp)-fishingeutrophication/turbidityhabitat changecauses: climate , SLRen fisherybivalve harvestinghuman activity impacts onphysics and species level andindirectly through foodweb


Conclusions• Silt transport in watersystems with intertidal areas can beinfluenced by occurrence of ecosystem-engineers.• Change of benthos species composition in time can influencethe sensitivity of the system for erosion.• The residence time of silt in the ‘active’ bed toplayer is short. Incombination with species shifts this can introduce drasticchanges of bed composition on small time and space scales.• Deepening of a water system decreases the influence ofstabilizing species and therefore could increase sensitivity forerosion.• Effect of largescale climate change can be local and quick andnon linear (via ‘storminess’ en species shifts).


Insights for management• We need to focus more on dynamics of silt. Time scales arerelatively short and the influence of eco-engineers is large.Many species are sensitive to sediment composition andturbidity.• Intertidal species change water quality on water system scale,this knowledge should be included in Water FrameworkDirective and Habitat Directive management.• Observed trends in WS indicate shifts toward dominance ofdestabilisers. This could lead to more sharp gradients of bedcomposition in the WS. This process is not per definitionreversible.• Changing bed composition leads to changed speciescompositon and will influence habitats of (protected) birdspecies.• Adequate (synoptic) monitoring is lacking and is urgentlyneeded given the expected impacts of climate change.


Use of E-Engineers in coastal protection• Oyster and musselbeds influence currents, wavesand sediment transport• These filterfeeders will deposit an extra silt-flux onthe bed as pellets.• Idea: Combination of both impacts can help to protectsaltmarshes for erosion and provide an extrasediment flux toward the saltmarshes.• A living reef will grow with the bed level.• We are now executing a field experiment with oystersin the Eastern Scheldt, to assess the effectiveness anvalidate model predictions.


Musselbed changes erosion patternyellow: nettsedimentationincluding pelletproductionWave and currentcoefficients calibratedon laboratoryexperiments


Construction of Oyster reef in EasternScheldt400m reefharvestareaCreation: November 2006Phys+BioMonitoring: 2006-2008


Diverse Dike concept• A lot of hard coastal infrastructure in NL, design andmaterials not very suitable for hard substrate species.• Create added value by enhancing its biodiversity andbio-productivity.• Create integrated designs for harbour walls anddeep- and shallow ‘classic’ dikes and dams (2006).• Spin-off for watersystem quality (WFD!) by providingextra habitats for specific species such as migratingfish or extra filter feeding capacity.• Field pilots in 2007 in cooperation with Harbour ofRotterdam and Government.


front view of‘reef’mhwmlwlimit lightside-viewmacro-algae inphotic zonefish, lobstersandbivalve ‘reef’large scalestructures,overhangs,‘caves’Deep ‘enriched’ harbourwall designporeous ‘reef’-3D structurewith holes andoverhangs


Further applications• Influence of saltmarshes on storm surgeduring hurricane Katrina event• Influence of mangroves on tsunami waveIntegrated approach is necessary, cooperationbetween different institutes is crucial!


Thank you!Contact:• mindert.devries@wldelft.nl• www.biogeomorphology.org

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