给排水外文翻译原稿.docx

给排水外文翻译原稿.docx

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给排水外文翻译原稿

Relationsbetweentriazineflux,catchmenttopographyanddistance

betweenmaizefieldsandthedrainagenetwork

F.Colina,*,C.Puecha,G.deMarsilyb,1

aUMR“Syste`mesetStructuresSpattiaux”,Cemagref-ENGREF500,rueJ.F.Breton34093,MontpellierCedex05,France

bUMR“StructureetFonctionementdesSyste`mesHydriquesContinentaux”,Universite´P.etM.Curie4,Pl.Jussieu75252,

ParisCedex05,France

Received5October1999;revised27April2000;accepted19June2000

Abstract

Thispaperputsforwardamethodologypermittingtheidentificationoffarmingplotscontributingtothepollutionofsurfacewaterinordertodefinethezonesmostatriskfrompesticidepollution.Weworkedatthescaleofthesmallagriculturalcatchment（0.2–7.5km2）asitrepresentstheappropriateleveloforganisationforagriculturalland.Thehypothesistestedwas:

thefartherafieldundergoingapesticidetreatmentisfromachannelnetwork,theloweritsimpactonpollutionatthecatchmentoutlet.

Thestudyarea,theSoussoncatchment（120km2,Gers,France）,hasa“herringbone”structure:

50independenttributariessupplythemaindrain.Pesticidesalesshowthatatrazineisthemostfrequentlyusedcompoundalthoughitisonlyusedfortreatingmaizeplotsandthatitsapplicationrateisconstant.Intwowinterinter-stormmeasurementexercises,triazinefluxvalueswerecollectedatabout30independentsub-basinoutlets.

Thecontributoryareasaredefined,withtheaidofaGIS,asdifferentstripsaroundthechannelnetwork.Thecorrelationbetweenplotsundermaizeincontributoryzonesandtriazinefluxatrelatedsub-basinoutletsisstudiedbyusingnon-parametricandlinearcorrelationcoefficients.Finally,themostpertinentcontributoryzoneisassociatedwiththebestcorrelationlevel.Acatchmenttypology,basedonaslopecriterion,allowsustoconcludethatinsteepslopecatchments,thecontributoryareaisbestdefinedasa50mwidestriparoundthechannelnetwork.Inflatzones,theagriculturaldrainagenetworkisparticularlywelldeveloped:

artificialdrainsextendthechannelnetworkextractedfromthe1/25.000scaletopographicmap,andthetotalsurfaceareaofthecatchmentmustbetakentoaccount.q2000ElsevierScienceB.V.Allrightsreserved.

Keywords:

Pesticidecatchment;GISartificialnetwork

1.Introduction

Theuseofpesticidesinwesternagriculturedatesbacktothemiddleofthe19thcentury（Fournier,1988）.Sincethen,becauseoftheirintensiveuse,yieldshaveincreasedandthedemandforagriculturalproductshasbeensatisfied.However,thepollutioncreatedbytheirusethreatensbothdrinkingwaterresourcesandtheintegrityofecosystems.Therefore,thereisagreatdemandforthereductionofpollution.Theremedieslieinchangesinthewaythatagriculturallandismanaged.TheproblemofagriculturalJournalnon-pointsourcepollutionbypesticidesmustbetakenfromthefield,thelevelofaction,tothecatchment,thelevelofcontrolofthewaterresource.

Betweenthesetwospatialscales,differentlevelsoforganisationcanbefound.Fields,groupsoffields,basinsandmaincatchment,canbeviewedtogetherasnestedsystems（Bureletal.,1992）.Foreachscalelevel,themainprocessesgoverningwatermovementandsolublepollutanttransportaredifferent,asarethevariablescharacterisingthesystem（Lebel,1990）:

flowinmacroporesatlocalscale,preferentialflowpathsatthehillslopescale,flowsinconnectionwith

therepartitionofdifferentsoilsatthecatchmentscale,geologyinfluenceattheregionalscale（Blo¨schandSivapalan,1995）.

Atthefieldlevel,anexperimentalapproachcanbeusedandtherelativeweightofeachvariablecanbeexperimentallytested（Scheunert,1996;Bengtsonetal.,1990）.Themajorfactorsthatconcernagriculturalpracticeshavebeenidentifiedandmanyagriculturalmanagementindicatorshavebeendeveloped（Bockstalleretal.,1997）.

Nevertheless,thisapproachcannotbeappliedatthecatchmentscaleforseveralreasons:

theneedtomeasurethepollutionandtheenvironmentalfactorssimultaneously,multiplemeasurementdifficulties,thecomplexityofanalysis.Thevariabilityofobservationshastemporalandspatialcomponents.Raininducespesticideleachingandthereforecauses

temporaryhighpesticideconcentrationsinthewater;thecloserthepesticidespreadingdateinthe

fieldistothemeasurement,thegreatertheconcentrationlevels（Seuxetal.,1984;Reme,1992;LarocheandGallichand,1995）.TheextensiveuseofGeographicalInformationSystem（GIS）hasmadeitpossibletoanalysetheimpactonthepollutionofthespatialcharacteristicsofagriculturalzones（BattaglinandGoolsby,1996）.Butsofar,theresultsoftheseexperiments

haveonlyledtoanapproximateestimateoftherisks（TimandJolly,1994）.

Inordertoprogressinthesearchforwaystoreducepesticidepollution,itwouldbeworthwhiletoimproveourassessmentofhowspatialstructureandorganisationaffectsthelevelsofpollutantsmeasured.Thispaperpresentstheresultsofastudythatconcernsaparticularaspectoftheinfluenceofspatialorganisationonpesticidetransfer:

theeffectsofthedistancebetweenthecroplandandthechannelnetwork.Thelongerthedistancebetweenacultivatedfieldandariver,thegreatertheretentionanddegradationprocesses（Leonard,1990;Belamieetal.,1997）.Onemightthereforeimaginethatthegreaterthedistance,thelowerthepollutionlevel.However,

fewstudieshavegivenanumericalvaluetothecriticaldistanceatwhichafielddoesnotinfluenceriverpollutionsignificantly.Usually,whendealingwithriskzonedefinition,expertsestablishanarbitrarydistance（Bouchardy,1992）.Ourmaingoalistodeterminethroughspatialanalysisthecriticaldistancefromahydrographicnetwork.Thezonesmostatriskfrompesticides,includingtheplots,whichcontributemostofthepollution,canthenbedetermined.

Thestudyarea,theSoussoncatchment（Gers,France）hascertainphysicalcharacteristics,whichallowssamplingofmostoftheindependentsubbasins,definedhereasagriculturalproductionzones.Itsparticularmorphologymadethecomparativestudyoftheproductionzonespossible.Themethodinvolvesastatisticalcomparisonbetweenpollutionmeasurementsandspatialcharacteristicsofthecatchments.Inordertoestablishtheboundariesof

thecontributingareas,thepollutionfluxmeasuredattheproductionzoneoutletiscomparedtothelandcover,estimatedwithinstripsofvariablewidtharoundthechannelnetwork.Resultsareshownanddiscussedfromamainlypracticalviewpoint.

2.Thestudyareaandcollecteddata

2.1.Studyareadescription

ThestudyareaistheSoussoncatchment,insouthwesternFrance（Gers）.TheSoussonRiverisatributaryoftheriverGers.Thecatchmentareais120km2.The32kmlonghydrographicnetworkhasa‘herringbone’pattern:

53sub-basinswithfairlyhomogeneoussurfacesareasrangingfrom0.2to7.5km2servethecentraldrain（Fig.1）.

Thewide,gentlyslopingandheavilycultivatedleftbank,differsfromtherightbank,whichisnarrow,steepandmainlymadeupofforestandpastureland.

TheSoussoncatchmentareaisexclusivelyagricultural.Thereisnoindustryorsettlementofmorethan200inhabitants.Thetwomaincropscultivatedare

maizeandwinterwheat（17and15%ofthecatchmentsurfacearea,respectively）.Themaizefieldsareusuallysituated,ontheleftbank,intheupstreammiddleofthecatchmentarea,andalongthemainriver.

Therearetwotypesofsoil:

acalcareoussoil,whichisquitepermeable,andanon-calcareoussoilcalledlocally‘boulbenes’withantoplimoneouslayerandalowersiltylayer.Inordertoavoidthestagnationofwaterintheupperlayercausedbythesiltyimpermeablelayer,thefieldsonboulbenesoilareartificiallydrained.Maizeiscultivatedforpreferenceonthis

typeofsoil.

Nosignificantaquiferhasbeenfoundinthecatchment,asthesubstratumisratherimpervious（clays）.

2.2.Collecteddata

2.2.1.Spatialdata

AGISwasdevelopedforthearea,whichcontainsthefollowinginformationlayers:

²thehydrographicnetworkandthecatchmentboundariesdigitizedfrom1/25.000scaletopographicmap;

²agriddedDigitalElevationModel（DEM）ofthezoneprovidinglandsurfaceslopesgeneratedfromDEMwitharesolutionof75m;

²theboundariesofcultivatedfieldsdigitizedfromaerialphotosatscaleof1/15.000;

²landcoverforboth1995and1996wasdefinedindetailinthestudyarea.For1997,landcoverwasidentifiedbyremotesensing.KnowledgeofagriculturalantecedentsenhancedtheclassificationofaSPOT（SatellitePourl0ObservationdelaTerre）image.Asaresult,themaizeareasfortheentireSoussoncatchmentweredeterminedfor1995,1996and1997（Fig.2）.

GISfunctionsarecapableofdeterminingthelandcoverofeachcatchmentbyintersectingthetwoinformationlayers“landcover”and“catchmentboundaries”,ordefiningazoneofconstantwidtharoundthehydrographicnetwork,whichiscalledthebufferzone.

Inordertoevaluatethepesticideapplicationrate,figuresforlocalpesticidesaleswerecollected.Atrazine,alachlorandglyphosatearethemostcommonlyusedcompounds,atrazinefaroutstripstheotherstriazinesasthemostfrequentlyusedproduct（tentimeslesssimazineissold）.Inthisregion,atrazineisonlyusedinmaizecultivation.Theapplicationrate（massofatrazinesold/maizesurfacearea）doesnotvaryfromonemunicipalitytoanother.

Tosimplifytheinvestigations,wechosetostudytheatrazinespreadonmaizeplotsinMay.Weassumethatallthemaizeplotsaretreatedwithatrazineandthattheapplicationrateisuniform.

2.2.2.Waterpollutiondata

Twoseri