外文翻译缓解湖泊富营养化放开氮控制并专注于磷的减排节选.docx

外文翻译缓解湖泊富营养化放开氮控制并专注于磷的减排节选.docx

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外文翻译缓解湖泊富营养化放开氮控制并专注于磷的减排节选

中文4700字，2980单词，16700英文字符

出处：

ProgressinNaturalScience19（2009）1445–1451

原文

MitigationofLakeEutrophication:

LoosenNitrogenControlandFocusOnPhosphorusAbatement

HaijunWang,HongzhuWang

Abstract

Traditionally,nitrogencontrolisgenerallyconsideredanimportantcomponentofreducinglakeeutrophicationandcyanobacteriablooms.However,thisviewpointisrefutedrecentlybyresearchersinChinaandNorthAmerica.Inthepresentpaper,thetraditionalviewpointofnitrogencontrolispointedouttolackascientificbasis:

theN/Phypothesisisjustasubjectiveassumption;bottlebioassayexperimentsfailtosimulatethenaturalprocessofnitrogenfixation.Ourmulti-yearcomparativeresearchinmorethan40Yangtzelakesindicatesthatphosphorusisthekeyfactordeterminingphytoplanktongrowthregardlessofnitrogenconcentrationsandthattotalphytoplanktonbiomassisdeterminedbytotalphosphorusandnotbytotalnitrogenconcentrations.Theseresultsimplythat,inthefield,nitrogencontrolwillnotdecreasephytoplanktonbiomass.Thisfindingissupportedbyalong-termwhole-lakeexperimentfromNorthAmerica.Theseoutcomescanbegeneralizedintermsthatareductioninnitrogenloadingmaynotdecreasethebiomassoftotalphytoplanktonasitcanstimulatebloomsofnitrogen-fixingcyanobacteria.Tomitigateeutrophication,itisnotnitrogenbutphosphorusthatshouldbereduced,unlessnitrogenconcentrationsaretoohightoinducedirecttoxicimpactsonhumanbeingsorotherorganisms.Finally,detailsareprovidedonhowtoreducecontrolsonnitrogenandhowtomitigateeutrophication.

KeywordsLakeeutrophication;Cyanobacteriabloom

1.Introduction

Eutrophicationofwatersisthephenomenonofanecosystembecomingmoreproductivebynutrientenrichment,stimulatingprimaryproducers.Itisusuallycharacterizedbyalgalblooms,causingwaterqualitydeteriorationandfishkills.Itisbecomingaglobalenvironmentalcrisis.InChina,theproblemoflakeeutrophicationisextremelysevere,withfrequentcyanobacteriabloomsthreateningtheecologyofwaters,economicdevelopmentandsocietystability.ThemostrepresentativecaseisthecyanobacteriabloomthatoccurredinLakeTaihuin2007,resultinginashortageofdrinkingwateranddomesticwaterfor5millioncitizensinWuxi,JiangsuProvince.Therefore,mitigationoflakeeutrophicationandcyanobacterialbloomisofgreatimportanceinChinaandtheworld.

Tomitigateeutrophicationandcyanobacterialblooms,nutrientcontrolisafundamentalprocess.Traditionally,besidesphosphoruscontrol,nitrogencontrolisgenerallyconsideredanecessarypractice.Abundantfundshavebeenspentonnitrogenremovalduringwastewatertreatmentprocesses.However,recentresearchesinChinaandNorthAmericasuggestachangetothetraditionalpracticeofnitrogenremovalforinlandwaters:

tomitigateeutrophication,itisnotnitrogenbutphosphorusthatshouldbereduced.Thisfindingisofcriticalimportanceforthepracticeoflakerestoration.

Inthispaper,thetraditionalviewpointofnitrogencontrolispointedoutfirsttolackaconclusivescientificbasis.Then,newresearchesareintroducedtoelaborateageneralrule:

reductioninnitrogenloadingcannotdecreasetotalphytoplanktonbiomass,butstimulatesbloomsofnitrogen-fixingcyanobacteria.Furtheranalysesproceededtoelaborateonthesignificanceofthisgeneralruleforthestrategytocontrolthesourceofnutrients.Intheend,suggestionsonlakerestorationareproposedindetail.

2.Thetraditionalviewpointofnitrogencontrollacksconclusivescientificbases

ThetraditionalviewpointoflimitingnutrientcontrolonphytoplanktonbiomassisbasedmostlyonconsiderationsofN/P（ratiooftotalnitrogentototalphosphorus）andonbottlebioassayexperiments.However,thefollowinganalysesindicatethatboththehypothesisandtheexperimentarenotconclusive.

2.1.TheN/Phypothesisisasubjectiveassumption

Generally,lakeshavebeenregardedaslimitedbyphosphorusifTN/TPwasrelativelylarge（suchasTN/TP>17）,limitedbynitrogenifTN/TPwasrelativelysmall（suchasTN/TP<10）andcolimitedbynitrogenandphosphoruswhenTN/TPwasintermediate（suchas10

N:

PproposedbyRedfieldasacriteriontoassessnutrientlimitation.Again,theRedfieldratioisnotauniversaloptimumratio,butanaverageofspecies-specificratios.TheoptimumN/Pratiosvarygreatlyamongvariousfreshwaterphytoplanktonspecies,from4.1to133.3.Obviously,itisalmostimpossibletosetaspecific“cut-off”ratiotoidentifyalimitingnutrient（s）foramulti-speciescommunity.

ByanalyzingtheregressionsandscatterplotsofphytoplanktonChlaorophyllwithnitrogenandphosphorus,SakamotofirstproposedtheN/Phypothesis.However,whenprobingintotheevidence,wefindthathisconclusionisjustasubjectivejudgmentonthepatternsofthescatterplots.Inhisanalysis,henotedthreepointswithaN/Pratiolargerthan15–17deviating.HeconcludedthatphosphorusbecamethecriticallimitingfactoriftheN/Pratiowaslargerthan15–17.Infact,therearetenpointswiththislevelofN/Pratioandtheleftsevenpointsfellexactlyontheregressionline.Obviously,suchareasoningbasedonminorpointsisnotright.Similarly,heconcludedthatphytoplanktonwaslimitedbynitrogenwhenN/Pwaslessthan9–10basedontwooutlierpoints,whenanalyzingtheregressionrelationshipbetweenlog（TN）andlog（Chla）.Therefore,thisearliestempiricalevidencedoesnotsupporttheN/Phypothesis.

ManyresearchershavefollowedtheprinciplesespousedbySakamototoanalyzethelimitingnutrientandvariationsunderdifferentN/Pratios.However,alltheanalyseshavebeenperformedwithoutstrictstatisticaltests,failingtoprovethatthedependenceofphytoplanktononnitrogenandphosphorusaresignificantlydifferentunderdifferentN/Pratios.

Inconclusion,throughlogicalreasoningandempiricalanalyses,theN/Phypothesisisfoundtobejustasubjectiveassumptionwithoutconclusiveevidence.

2.2.Bottlebioassayexperimentsaretoosmallinscaletosimulatethenaturalprocessofnitrogenfixation

Bottlebioassayexperimentshavealsolongbeenusedtodemonstratethelimitingnutrientofphytoplanktoninawaterbody.Theexperimentsareusuallyperformedinanenclosedcontainertodiscriminatethelimitingnutrientbyobservingthegrowthofphytoplanktonafternutrientaddition.Theygenerallylastaperiodbetweenseveralhoursto1week.Ifgrowthofphytoplanktonisstimulatedbytheadditionofsomenutrient,thisnutrientisconsideredtobethelimitingfactor.Duetotheirsmallscaleintimeandspace,theseexperimentsfailtosimulatesomeimportantprocessesinrealopensystemssuchasbiologicalnitrogenfixation.Therefore,bottlebioassayexperimentscannotprovethelong-termexistenceofnitrogenlimitationinthefield.

3.Newresearchesfindthatnitrogencontrolfailstorestraintotalphytoplankton,butstimulatesbloomsofnitrogen-fixingcyanobacteria

InMay2008,ourarticledisprovedtheN/Phypothesisbasedonregionalcomparativestudies.InAugust2008,anarticlebyresearchersfromNorthAmericaindicatedthatnitrogencontrolmightstimulatenitrogen-fixingcyanobacteriabasedonalong-termwhole-lakeexperiment.Accordingly,itappearsthatreductioninnitrogenloadingcannotdecreasethebiomassoftotalphytoplankton.Itisalsologicalwhencomparingthecyclingcharacteristicsofnitrogenandphosphorus.

3.1.RegionalresearchintheYangtzeBasin

TotesttheN/Phypothesisonalargescale,weanalyzedtherelationshipsofChlaorophyllawithtotalnitrogenandtotalphosphorusbasedonmulti-yearinvestigationsofmorethan40Yangtzelakes.AlmostalltheTP-ChlaregressionshadhigherR2valuesandlowerpercentagepredictiveerrorthanthoseofTN-Chlaregressions,indicatingthesuperiorityofTPoverTNasapredictor.

BecausedifferentthresholdsofTN/TPratioshavebeenproposedintheliterature,wefurthercomparedthedifferencesofR2valuesbetweenTP-ChlaandTN-ChlaregressionsoverthecompleteTN/TPspectrum.Theresultsshowedthat28R2valuesofTP-ChlaregressionswerehigherthanthoseofTN-ChlaregressionsovertheentireTN/TPspectrum.AccordingtothetraditionalN/Phypothesis,thesecasesshouldbelimitedbyphosphorusandhaverelativelyhighTN/TPratios.However,theywerenotconfinedtoanyspecificregionofhigherTN/TPratios,butdistributedevenlybetween5and50.ItfurtherdemonstratesthefailureofTN/TPtoindicatenutrientlimitation.

ForagivenamountofTP,ChlavariedregardlessofthechangesofTN.Thatis,withintheTN/TPrangeofthepresentresearch,Chla/TPtendstowardsaspecificvalue.However,foragivenamountofTN,ChlaincreasedrapidlywiththeincreaseinTP.Therefore,inthefield,thetotalphytoplanktonbiomassisnotdeterminedbyTNbutbyTP.

OurresearchdisprovedthetraditionalviewpointofusingN/Pasanindextodiscriminatenutrientlimitingphytoplankton.WeareoftheopinionthatTPistheprimaryfactorregulatingphytoplanktonChlaregardlessoftheconcentrationofTN.

3.2.Long-termwhole-lakeexperimentsinCanada

InLake227,asmalllakeintheExperimentalLakesArea（ELA）ofOntario,Canada,researchersfromCanadaandtheUSAhaveperformedwhole-lakefertilizationexperimentsfor37years.Thelakehasbeenfertilizedwithconstantphosphorusanddecreasingnitrogenaddition.Int