流域非點源污染過程動態模擬及其定量控制一、本文概述Overviewofthisarticle隨著人類活動的不斷加劇，非點源污染已成為流域水體污染的主要來源之一，對生態環境和人體健康構成嚴重威脅。非點源污染由于其來源廣泛、過程復雜、難以監測等特點，一直是環境科學領域的研究難點和熱點。因此，開展流域非點源污染過程的動態模擬及其定量控制研究，對于保護和改善流域生態環境質量，促進可持續發展具有重要意義。本文旨在通過深入研究流域非點源污染過程，構建動態模擬模型，提出定量控制措施，為流域水環境治理提供科學依據和技術支持。Withthecontinuousintensificationofhumanactivities,non-pointsourcepollutionhasbecomeoneofthemainsourcesofwaterpollutioninriverbasins,posingaseriousthreattotheecologicalenvironmentandhumanhealth.Nonpointsourcepollutionhasalwaysbeenaresearchdifficultyandhotspotinthefieldofenvironmentalscienceduetoitswiderangeofsources,complexprocesses,anddifficultyinmonitoring.Therefore,conductingdynamicsimulationandquantitativecontrolresearchonnon-pointsourcepollutionprocessesinriverbasinsisofgreatsignificanceforprotectingandimprovingtheecologicalenvironmentqualityofriverbasinsandpromotingsustainabledevelopment.Thisarticleaimstoprovidescientificbasisandtechnicalsupportforwatershedwaterenvironmentgovernancebyconductingin-depthresearchonnon-pointsourcepollutionprocesses,constructingdynamicsimulationmodels,andproposingquantitativecontrolmeasures.本文首先介紹了非點源污染的基本概念、特點及其對環境的影響，闡述了開展非點源污染研究的必要性和緊迫性。然后，詳細綜述了國內外在非點源污染模擬和控制方面的研究進展和現狀，指出了當前研究中存在的問題和不足。在此基礎上，本文提出了流域非點源污染過程動態模擬的研究思路和方法，包括模型的構建、參數的確定、模型的驗證和應用等方面。本文還探討了流域非點源污染定量控制的策略和方法，包括源頭控制、過程控制和末端控制等。Thisarticlefirstintroducesthebasicconcepts,characteristics,andimpactontheenvironmentofnon-pointsourcepollution,andelaboratesonthenecessityandurgencyofconductingresearchonnon-pointsourcepollution.Then,adetailedreviewwasconductedontheresearchprogressandcurrentstatusofnon-pointsourcepollutionsimulationandcontrolathomeandabroad,pointingouttheproblemsandshortcomingsincurrentresearch.Onthisbasis,thisarticleproposesaresearchapproachandmethodfordynamicsimulationofnon-pointsourcepollutionprocessesinriverbasins,includingmodelconstruction,parameterdetermination,modelvalidation,andapplication.Thisarticlealsoexploresthestrategiesandmethodsforquantitativecontrolofnon-pointsourcepollutioninriverbasins,includingsourcecontrol,processcontrol,andendofpipecontrol.通過本文的研究，可以為流域非點源污染的有效治理提供理論支持和實踐指導，促進流域生態環境的改善和可持續發展。本文的研究還可以為其他類似流域的非點源污染治理提供參考和借鑒。Throughtheresearchinthisarticle,theoreticalsupportandpracticalguidancecanbeprovidedfortheeffectivemanagementofnon-pointsourcepollutioninthewatershed,promotingtheimprovementoftheecologicalenvironmentandsustainabledevelopmentofthewatershed.Thisstudycanalsoprovidereferenceandinspirationforthecontrolofnon-pointsourcepollutioninothersimilarwatersheds.二、流域非點源污染產生機理分析AnalysisoftheMechanismofNonpointSourcePollutioninWatersheds流域非點源污染，也稱為面源污染，是指在大氣降水（包括雨、雪、霜、露、霧、雹等）和融雪產生的徑流沖刷作用下，泥沙和溶解的及固體的污染物從非特定的地域，在降水（或融雪）產生徑流沖刷作用下，通過徑流過程而匯入受納水體（包括河流、湖泊、水庫和海灣等）并引起水體的富營養化或其他形式的污染。與點源污染相比，非點源污染具有空間范圍的廣泛性、發生時間的隨機性、排放方式的不確定性、污染負荷的隱蔽性、監測與控制的困難性等特點。Nonpointsourcepollutioninwatersheds,alsoknownasnon-pointsourcepollution,referstotherunofferosioncausedbyatmosphericprecipitation(includingrain,snow,frost,dew,fog,hail,etc.)andsnowmelt.Sedimentsanddissolvedandsolidpollutantsfromnon-specificareas,undertherunofferosioncausedbyprecipitation(orsnowmelt),enterthereceivingwaterbodies(includingrivers,lakes,reservoirs,bays,etc.)throughtherunoffprocessandcauseeutrophicationorotherformsofpollutionofthewaterbodies.Comparedwithpointsourcepollution,nonpointsourcepollutionhasthecharacteristicsofwidespatialrange,randomnessofoccurrencetime,uncertaintyofemissionmethods,concealmentofpollutionload,anddifficultyinmonitoringandcontrol.非點源污染產生機理較為復雜，涉及大氣降水、地表徑流、土壤侵蝕、水體凈化等多種自然和人為因素。大氣降水是引發非點源污染的直接原因，它形成的徑流會沖刷地表，攜帶走地表附著的污染物質，如農藥、化肥、畜禽糞便等。地表徑流是非點源污染的主要傳輸途徑，它會將地面上的污染物質輸送到河流、湖泊等水體中。土壤侵蝕也是非點源污染產生的重要原因，它會破壞地表土壤結構，使土壤中的污染物質更易被徑流帶走。Themechanismofnon-pointsourcepollutionisrelativelycomplex,involvingvariousnaturalandhumanfactorssuchasatmosphericprecipitation,surfacerunoff,soilerosion,andwaterpurification.Atmosphericprecipitationisthedirectcauseofnon-pointsourcepollution.Therunoffitformswillwashawaythesurfaceandcarryawaypollutantsattachedtothesurface,suchaspesticides,fertilizers,andanimalmanure.Surfacerunoffisthemaintransportpathwayofnon-pointsourcepollution,whichtransportspollutantsfromthegroundtorivers,lakes,andotherwaterbodies.Soilerosionisalsoanimportantcauseofnon-pointsourcepollution,whichcandamagethesurfacesoilstructureandmakeiteasierforpollutantsinthesoiltobecarriedawaybyrunoff.非點源污染還受到地形、地貌、植被覆蓋、土地利用方式等自然因素的影響。例如，地形陡峭的地區更易發生水土流失，導致非點源污染加重；植被覆蓋良好的地區，由于土壤保持能力強，非點源污染相對較少。人類活動也對非點源污染產生重要影響，如農業生產中的化肥、農藥使用，城市建設中的土地硬化等，都會增加非點源污染負荷。Nonpointsourcepollutionisalsoinfluencedbynaturalfactorssuchasterrain,topography,vegetationcover,andlandusepatterns.Forexample,areaswithsteepterrainaremorepronetosoilerosion,leadingtoincreasednon-pointsourcepollution;Areaswithgoodvegetationcoveragehaverelativelylessnon-pointsourcepollutionduetotheirstrongsoilconservationability.Humanactivitiesalsohaveasignificantimpactonnon-pointsourcepollution,suchastheuseoffertilizersandpesticidesinagriculturalproduction,andlandhardeninginurbanconstruction,whichwillincreasetheburdenofnon-pointsourcepollution.流域非點源污染產生機理涉及多個方面，要有效控制非點源污染，需要從多個角度入手，綜合考慮自然和人為因素，采取科學合理的措施，減少污染負荷，保護水環境安全。Themechanismofnon-pointsourcepollutioninriverbasinsinvolvesmultipleaspects.Toeffectivelycontrolnon-pointsourcepollution,itisnecessarytostartfrommultipleperspectives,comprehensivelyconsidernaturalandhumanfactors,takescientificandreasonablemeasures,reducepollutionloads,andprotectwaterenvironmentsafety.三、流域非點源污染動態模擬體系構建ConstructionofDynamicSimulationSystemforNonpointSourcePollutioninRiverBasin流域非點源污染的動態模擬是理解和控制污染的關鍵環節。針對非點源污染的復雜性、多變性和不確定性，本文提出了一種流域非點源污染動態模擬體系的構建方法。Thedynamicsimulationofnon-pointsourcepollutioninawatershedisakeylinkinunderstandingandcontrollingpollution.Thispaperproposesamethodforconstructingadynamicsimulationsystemofnon-pointsourcepollutioninawatershed,inresponsetothecomplexity,variability,anduncertaintyofnon-pointsourcepollution.該模擬體系以地理信息系統（GIS）為基礎，結合遙感（RS）技術，對流域內的地形、地貌、土地利用、植被覆蓋等基礎信息進行精確獲取和空間化表達。這些信息是理解流域內污染物產生、遷移和轉化過程的基礎。ThissimulationsystemisbasedonGeographicInformationSystems(GIS)andcombinesremotesensing(RS)technologytoaccuratelyobtainandspatiallyexpressbasicinformationsuchasterrain,topography,landuse,andvegetationcoverinthewatershed.Thesepiecesofinformationarethefoundationforunderstandingtheprocessesofpollutantgeneration,migration,andtransformationwithinthewatershed.體系通過集成水文模型、水質模型和污染物運移模型，構建了一個綜合的流域非點源污染動態模擬模型。該模型能夠模擬不同降雨條件下，污染物在流域內的產生、遷移、轉化和輸出過程，為污染控制提供科學依據。Thesystemintegrateshydrologicalmodels,waterqualitymodels,andpollutanttransportmodelstoconstructacomprehensivedynamicsimulationmodelfornon-pointsourcepollutioninthewatershed.Thismodelcansimulatethegeneration,migration,transformation,andoutputprocessesofpollutantsinthewatershedunderdifferentrainfallconditions,providingscientificbasisforpollutioncontrol.再次，體系注重數據的實時獲取和模型的動態更新。通過在線監測設備，實時獲取流域內的降雨、徑流、水質等數據，對模型進行動態校準和更新，確保模擬結果的準確性和實時性。Onceagain,thesystemfocusesonreal-timedataacquisitionanddynamicmodelupdates.Throughonlinemonitoringequipment,real-timerainfall,runoff,waterqualityandotherdatawithinthewatershedareobtained,andthemodelisdynamicallycalibratedandupdatedtoensuretheaccuracyandreal-timeperformanceofsimulationresults.該模擬體系還具備決策支持功能。通過對模擬結果的分析和解讀，可以為流域管理者提供針對性的污染控制措施建議，幫助決策者制定科學、有效的非點源污染控制策略。Thesimulationsystemalsohasdecisionsupportfunctions.Byanalyzingandinterpretingthesimulationresults,targetedpollutioncontrolmeasurescanbeprovidedtowatershedmanagers,helpingdecision-makersdevelopscientificandeffectivenonpointsourcepollutioncontrolstrategies.本文構建的流域非點源污染動態模擬體系，不僅具有高度的科學性和實用性，而且能夠為流域非點源污染的有效控制提供有力支持。Thedynamicsimulationsystemfornon-pointsourcepollutioninthewatershedconstructedinthisarticlenotonlyhashighscientificandpracticalsignificance,butalsoprovidesstrongsupportfortheeffectivecontrolofnon-pointsourcepollutioninthewatershed.四、流域非點源污染定量控制策略Quantitativecontrolstrategyfornon-pointsourcepollutioninriverbasins流域非點源污染的有效控制需要采取一系列綜合性、系統性的策略。這些策略不僅包括工程技術措施，也涉及政策制定、公眾教育和環境管理等多個方面。Effectivecontrolofnon-pointsourcepollutioninriverbasinsrequiresaseriesofcomprehensiveandsystematicstrategies.Thesestrategiesnotonlyincludeengineeringandtechnicalmeasures,butalsoinvolvemultipleaspectssuchaspolicyformulation,publiceducation,andenvironmentalmanagement.工程技術措施是減少非點源污染的關鍵手段。這包括建設水土保持設施，如梯田、植被覆蓋、緩沖帶等，以減少土壤侵蝕和營養物流失。建設雨水收集和處理系統，如雨水花園、綠色屋頂等，能夠有效地截留和處理雨水中的污染物。Engineeringandtechnicalmeasuresarekeymeanstoreducenon-pointsourcepollution.Thisincludestheconstructionofsoilandwaterconservationfacilities,suchasterraces,vegetationcover,bufferzones,etc.,toreducesoilerosionandnutrientloss.Constructingrainwatercollectionandtreatmentsystems,suchasrainwatergardens,greenroofs,etc.,caneffectivelyinterceptandtreatpollutantsinrainwater.農業是非點源污染的主要來源之一。因此，實施科學的農業管理措施至關重要。這包括推廣使用環保型肥料和農藥，減少化肥和農藥的過量使用；改進農業耕作方式，如采用輪作、間作等，以減少土壤侵蝕；建設農田水利工程，提高農田灌溉效率，減少灌溉水量的浪費和污染。Agricultureisoneofthemainsourcesofnon-pointsourcepollution.Therefore,implementingscientificagriculturalmanagementmeasuresiscrucial.Thisincludespromotingtheuseofenvironmentallyfriendlyfertilizersandpesticides,reducingtheexcessiveuseoffertilizersandpesticides;Improveagriculturalcultivationmethods,suchascroprotationandintercropping,toreducesoilerosion;Constructagriculturalwaterconservancyprojectstoimproveirrigationefficiencyandreducewasteandpollutionofirrigationwater.政府應制定和完善相關政策和法規，為非點源污染的控制提供法律保障。這包括制定嚴格的排放標準，限制污染物的排放；實施生態補償機制，對環境保護成效顯著的單位和個人給予獎勵；加強環境監管，對違法行為進行嚴厲打擊。Thegovernmentshouldformulateandimproverelevantpoliciesandregulationstoprovidelegalprotectionforthecontrolofnon-pointsourcepollution.Thisincludessettingstrictemissionstandardsandlimitingtheemissionofpollutants;Implementecologicalcompensationmechanismsandrewardunitsandindividualswhohaveachievedsignificantenvironmentalprotectionresults;Strengthenenvironmentalsupervisionandcrackdownseverelyonillegalactivities.公眾是非點源污染控制的重要參與者。因此，加強公眾教育和意識提升至關重要。政府和社會組織應積極開展環保宣傳活動，提高公眾對非點源污染的認識和重視程度；推廣環保理念和生活方式，鼓勵公眾采取環保行動，如減少使用化肥和農藥、節約用水等。Thepublicisanimportantparticipantinnon-pointsourcepollutioncontrol.Therefore,strengtheningpubliceducationandraisingawarenessiscrucial.Thegovernmentandsocialorganizationsshouldactivelycarryoutenvironmentalprotectionpublicityactivitiestoincreasepublicawarenessandawarenessofnon-pointsourcepollution;Promoteenvironmentalprotectionconceptsandlifestyles,encouragethepublictotakeenvironmentalactions,suchasreducingtheuseoffertilizersandpesticides,andconservingwater.加強環境管理和監測是確保非點源污染得到有效控制的重要手段。政府應建立健全環境管理和監測體系，定期對流域內的非點源污染進行監測和評估；建立信息共享平臺，及時發布環境信息和污染預警；加強跨部門、跨區域的協作和配合，形成合力推進非點源污染控制的良好局面。Strengtheningenvironmentalmanagementandmonitoringisanimportantmeanstoensureeffectivecontrolofnon-pointsourcepollution.Thegovernmentshouldestablishasoundenvironmentalmanagementandmonitoringsystem,andregularlymonitorandevaluatenon-pointsourcepollutioninthewatershed;Establishaninformationsharingplatformtotimelyreleaseenvironmentalinformationandpollutionwarnings;Strengthencrossdepartmentalandcrossregionalcollaborationandcooperation,andformagoodsituationofjointlypromotingnon-pointsourcepollutioncontrol.流域非點源污染的定量控制需要綜合運用工程技術措施、農業管理措施、政策制定與法規建設、公眾教育與意識提升以及環境管理與監測等多種策略。只有這樣，才能有效地減少非點源污染對環境和生態的影響，實現流域的可持續發展。Thequantitativecontrolofnon-pointsourcepollutioninriverbasinsrequiresthecomprehensiveapplicationofvariousstrategiessuchasengineeringtechnologymeasures,agriculturalmanagementmeasures,policyformulationandregulatoryconstruction,publiceducationandawarenessenhancement,aswellasenvironmentalmanagementandmonitoring.Onlyinthiswaycanweeffectivelyreducetheimpactofnon-pointsourcepollutionontheenvironmentandecology,andachievesustainabledevelopmentofthewatershed.五、案例分析Caseanalysis為了具體展示流域非點源污染過程的動態模擬及其定量控制的實際應用，本研究選擇了中國南方某典型山區流域作為案例進行深入分析。該流域地處亞熱帶季風氣候區，降雨充沛，地形復雜，非點源污染問題較為嚴重。Inordertodemonstratethedynamicsimulationandquantitativecontrolofnon-pointsourcepollutionprocessesinthewatershed,thisstudyselectedatypicalmountainouswatershedinsouthernChinaasacasestudyforin-depthanalysis.Thewatershedislocatedinthesubtropicalmonsoonclimatezone,withabundantrainfall,complexterrain,andseriousnon-pointsourcepollutionproblems.我們對該流域進行了詳細的現場調查，收集了地形、氣候、土地利用、土壤類型等基礎數據。同時，通過布置多個監測站點，對流域內的水質進行了長期連續監測，獲得了豐富的水質監測數據。為了更準確地模擬非點源污染過程，我們還利用遙感技術和地理信息系統（GIS）對流域的空間數據進行了處理和分析。Weconductedadetailedon-siteinvestigationofthewatershedandcollectedbasicdatasuchasterrain,climate,landuse,andsoiltypes.Atthesametime,bysettingupmultiplemonitoringstations,thewaterqualityinthebasinwascontinuouslymonitoredforalongtime,andrichwaterqualitymonitoringdatawasobtained.Inordertomoreaccuratelysimulatetheprocessofnon-pointsourcepollution,wealsousedremotesensingtechnologyandgeographicinformationsystems(GIS)toprocessandanalyzethespatialdataofthewatershed.基于收集到的數據，我們采用了SWAT（SoilandWaterAssessmentTool）模型進行非點源污染的動態模擬。在模型構建過程中，我們根據流域的實際情況對模型參數進行了調整和優化，確保模型能夠更準確地反映流域的非點源污染過程。同時，我們還利用GIS技術對流域的空間數據進行了可視化處理，使得模擬結果更加直觀和易于理解。Basedonthecollecteddata,weusedtheSWAT(SoilandWaterAssessmentTool)modelfordynamicsimulationofnon-pointsourcepollution.Duringthemodelconstructionprocess,weadjustedandoptimizedthemodelparametersbasedontheactualsituationofthewatershed,ensuringthatthemodelcanmoreaccuratelyreflectthenonpointsourcepollutionprocessofthewatershed.Atthesametime,wealsoutilizedGIStechnologytovisualizethespatialdataofthewatershed,makingthesimulationresultsmoreintuitiveandeasytounderstand.通過模擬，我們得到了流域內不同時間段、不同區域的非點源污染負荷分布情況。分析結果顯示，該流域的非點源污染主要來源于農業面源污染和畜禽養殖污染。在降雨季節，由于降雨沖刷作用，大量污染物隨雨水進入河流，導致河流的水質明顯下降。我們還發現不同區域的非點源污染負荷存在較大差異，這主要與土地利用類型、地形地貌等因素有關。Throughsimulation,weobtainedthedistributionofnon-pointsourcepollutionloadsindifferenttimeperiodsandregionswithinthewatershed.Theanalysisresultsshowthatthenon-pointsourcepollutioninthewatershedmainlycomesfromagriculturalnon-pointsourcepollutionandlivestockandpoultrybreedingpollution.Duringtherainyseason,duetotheerosioncausedbyrainfall,alargeamountofpollutantsentertheriverwiththerainwater,resultinginasignificantdecreaseinthewaterqualityoftheriver.Wealsofoundthattherearesignificantdifferencesinnon-pointsourcepollutionloadsindifferentregions,whicharemainlyrelatedtofactorssuchaslandusetypes,terrainandlandforms.針對模擬結果，我們提出了一系列定量控制策略。針對農業面源污染，我們推廣了生態農業技術，如合理施肥、減少化肥農藥使用量等。針對畜禽養殖污染，我們提出了規模化養殖、糞污資源化利用等措施。我們還建議加強流域內生態修復工作，如植樹造林、水土保持等，以提高流域的生態環境質量。Weproposeaseriesofquantitativecontrolstrategiesbasedonthesimulationresults.Inresponsetoagriculturalnon-pointsourcepollution,wehavepromotedecologicalagriculturaltechnologies,suchasrationalfertilizationandreducingtheuseoffertilizersandpesticides.Wehaveproposedmeasuressuchaslarge-scalebreedingandresourceutilizationofmanuretoaddressthepollutioncausedbylivestockandpoultryfarming.Wealsosuggeststrengtheningecologicalrestorationworkwithinthewatershed,suchasafforestation,soilandwaterconservation,toimprovetheecologicalenvironmentqualityofthewatershed.為了評估定量控制策略的實施效果，我們在流域內選擇了幾個典型區域進行了試點。通過對比實施前后的水質監測數據，我們發現試點區域的水質得到了明顯改善。具體而言，氨氮、總磷等主要污染物的濃度均有所下降，達到了預期的治理效果。這表明我們所提出的定量控制策略是有效的，可以為其他類似流域的非點源污染治理提供參考和借鑒。Inordertoevaluatetheimplementationeffectofquantitativecontrolstrategies,weselectedseveraltypicalareaswithinthewatershedforpilottesting.Bycomparingthewaterqualitymonitoringdatabeforeandafterimplementation,wefoundthatthewaterqualityinthepilotareahassignificantlyimproved.Specifically,theconcentrationofmajorpollutantssuchasammonianitrogenandtotalphosphorushasdecreased,achievingtheexpectedtreatmenteffect.Thisindicatesthatourproposedquantitativecontrolstrategyiseffectiveandcanprovidereferenceandinspirationforthetreatmentofnon-pointsourcepollutioninothersimilarwatersheds.通過案例分析，我們展示了流域非點源污染過程的動態模擬及其定量控制的實際應用。實踐證明，通過科學的模擬和有效的控制策略，我們可以有效地降低流域的非點源污染負荷，改善水質狀況，保護生態環境。Throughcaseanalysis,wedemonstratethedynamicsimulationandpracticalapplicationofquantitativecontrolofnon-pointsourcepollutionprocessesinriverbasins.Practicehasproventhatthroughscientificsimulationandeffectivecontrolstrategies,wecaneffectivelyreducethenon-pointsourcepollutionloadinthewatershed,improvewaterquality,andprotecttheecologicalenvironment.六、結論與展望ConclusionandOutlook本研究針對流域非點源污染過程進行了深入的動態模擬研究，并探索了定量控制策略。通過構建高精度的非點源污染模型，我們成功模擬了不同時空尺度下的非點源污染過程，揭示了其動態變化特征。同時，本研究也提出了針對性的定量控制措施，包括土地利用優化、農業管理措施改善以及生態修復等，為非點源污染的防治提供了科學依據。研究結果表明，實施這些控制措施可以顯著降低流域內的非點源污染負荷，改善水質狀況，保護生態環境。Thisstudyconductedin-depthdynamicsimulationresearchonnon-pointsourcepollutionprocessesinriverbasinsandexploredquantitativecontrolstrategies.Byconstructingahigh-precisionnonpointsourcepollutionmodel,wesuccessfullysimulatedthenonpointsourcepollutionprocessatdifferentspatiotemporalscalesandrevealeditsdynamiccharacteristics.Meanwhile,thisstudyalsoproposestargetedquantitativecontrolmeasures,includinglanduseoptimization,agriculturalmanagementimprovement,andecologicalrestoration,providingscientificbasisforthepreventionandcontrolofnon-pointsourcepollution.Theresearchresultsindicatethatimplementingthesecontrolmeasurescansignificantlyreducethenon-pointsourcepollutionloadinthewatershed,improvewaterquality,andprotecttheecologicalenvironment.盡管本研究在流域非點源污染過程的動態模擬及定量控制方面取得了一定的成果，但仍存在許多需要進一步探討的問題。未來研究可以從以下幾個方面展開：Althoughthisstudyhasachievedcertainresultsinthedynamicsimulationandquantitativecontrolofnon-pointsourcepollutionprocessesinriverbasins,therearestillmanyissuesthatneedfurtherexploration.Futureresearchcanbeconductedfromthefollowingaspects:模型優化與改進：繼續完善非點源污染模型，提高模擬精度和可靠性，以更好地反映實際污染過程。同時，加強模型在不同流域、不同氣候條件下的適用性研究，為更多地區的非點源污染控制提供指導。Modeloptimizationandimprovement:Continuetoimprovethenonpointsourcepollutionmodel,improvesimulationaccuracy