Constructedwetlandsasacomponentoftheagriculturalla

Constructedwetlandsasacomponentoftheagriculturallandscape:MitigationofherbicidesinsimulatedrunofffromuplanddrainageareasM.A.Lockea,⇑,M.A.Weaverb,R.M.Zablotowiczc,R.W.Steinriedea,C.T.Brysonc,R.F.CullumaaUnitedStatesDepartmentofAgriculture,AgriculturalResearchService,NationalSedimentationLaboratory,WaterQuality&EcologyResearchUnit,598McElroyDrive,Oxford,MS38655,USAbUnitedStatesDepartmentofAgriculture,AgriculturalResearchService,BiologicalControlofPestsResearchUnit,Stoneville,MS,USAcUnitedStatesDepartmentofAgriculture,AgriculturalResearchService,CropProductionSystemsResearchUnit,Stoneville,MS,USAarticleinfoArticlehistory:Received21September2010Receivedinrevisedform13January2011Accepted14January2011Availableonline16February2011Keywords:AtrazineFluometuronWaterqualityWetlandabstractConstructedwetlandsarearecommendedpracticeforbufferingpollutantsourceareasandreceivingwaters.AwetlandconsistingofasedimenttrapandtwotreatmentcellswasconstructedinaMississippiDeltalakewatershed.A3-hsimulatedrunoffeventwasinitiated(2003)toevaluatefateandtransportofatrazineandfluometuronthroughthewetland.Watersampleswerecollectedduringarunoffsimulationandthenafterwardatselectedintervalsfor21d,andanalyzedfortheherbicides.Breakthroughpatternsforherbicideconcentrationsinwatersamplesduringthefirst20haftersimulatedrunoffshowedpeakconcentrationsinthefirst6h,withgradualtailingastheherbicidepulsewasdilutedinthesecond,exca-vated(deeper)cell.Atrazineandfluometuronconcentrationsinthefirst(shallower,non-excavated)cellaveraged12-and20-foldgreater,respectively,thanthoseinthesecondcellfollowingsimulatedrunoff,indicatingentrapmentinthefirstcell.Atrazineandfluometuronconcentrationsintheshallowercelldecreased32%and22%,respectively,9dfollowingsimulatedrunoff,indicatingeitherdegradationorsorptiontosoilorwetlandflora.Intheexcavatedcell,concentrationswereevenlower,andatrazinedeclinedmorerapidlythanfluometuron.Resultsindicateconstructedwetlandscanimprovedownstreamwaterqualitythoughsequestrationorprocessingofpollutants.PublishedbyElsevierLtd.1.IntroductionWetlandsareanintegralpartofmanylandscapes,oftenservingastransitionzonesbetweenuplandareasandwaterbodies.Assuch,wetlandsareasinkforavarietyofpollutants,givenproximitytoanthropogenicactivitiessuchasindustryoragriculture.Theintegrityofawetland,therefore,maydependuponitsabilitytoprocesscon-taminantsastheymovethroughthesystem.Althoughthephysical,biological,andchemicalprocessesarecomplex,interrelated,andnotcompletelyunderstood,factorscontributingtoeffectiveprocess-ingincludethesizeofthewetland,systemhydrology,vegetativecharacteristicsanddensity,proximitytocontaminantsources,andthenatureofthecontaminants(MitschandGosselink,2000).Constructingartificialwetlandsinvulnerableareaswherewet-landsdonotnaturallyexistmayprovideprotectionfrompollu-tantsmovingtowaterbodiesfromadjacentareas,andtheymaybemoreefficientinprocessingcontaminantsthannaturalwetlandsbecauseconstructedwetlandscanbetailoredtomeetspecificneeds.Significantresearchefforthasfocusedonthedevel-opmentandassessmentofconstructedwetlandsfortreatmentofwastefromurban,mining,andindustrialactivities(e.g.,BastianandHammer,1993;KadlecandKnight,1996).Inareasaffectedbyagriculture,theapplicationofconservationmanagementprac-ticessuchasconstructedwetlandshasreceivedattentionforattenuatingnon-pointcontaminationofsurfacewatersbysedi-ment,livestockwastewater,andagrochemicalsinrunoff(RodgersandDunn,1992;Hammeretal.,1993;Higginsetal.,1993;KadlecandKnight,1996;Cooperetal.,1998).Aspartofanintegratedagriculturalmanagementsystem,constructedwetlandscanbeusedinconjunctionwithotheredge-of-fieldmeasures,e.g.,vegeta-tivebufferstrips(Dabneyetal.,2006).Surfacewatercontaminationfromnon-pointsourcesisacon-cern.Herbicidesappliedtothesoilsurfaceinrowcropproductionaresusceptibletolossinsurfacerunoff,anddownstreamconserva-tionmeasuressuchasvegetatedconstructedwetlandsmayhelptominimizecontaminationofadjacentwaterbodies.Atrazineandfluometuronarecommonlyusedsoil-appliedherbicidesandarecandidatesforevaluationsoftheefficacyofconstructedwetlandsinremediatingrunofffromrowcropareas.Factorsthatmayinflu-encethedissipationofherbicidesinwetlandsystemsincludeveg-etationandassociateddecomposedlitter;highsoilorganiccarbon,anaerobicenvironment,andactivepopulationsofanaerobicandaerobicmicrobes(Stoeckeletal.,1997).0045-6535/$-seefrontmatterPublishedbyElsevierLtd.doi:10.1016/j.chemosphere.2011.01.034⇑Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](M.A.Locke).Chemosphere83(2011)1532–1538ContentslistsavailableatScienceDirectChemospherejournalhomepage:(Krutzetal.,2010)andwithinawetlandafterbio-augmentationofthesedimentwithsoilfromanenhanced-mineralizingatrazinespillsite(R