2015_NatureHazards_green tide

浒苔;绿潮;2015;海水水质;面积加权水质等级

NatHazards

DOI10.1007/s11069-015-1694-x

ORIGINALPAPER

Interpretingtheprogressiveeutrophicationbehind

theworld’slargestmacroalgalbloomswithwaterqualityandoceancolordata

QianguoXing1?LuigiTosi2?FedericaBraga2

XueluGao1?MengGao1?

Received:12January2015/Accepted:11March2015

ÓTheAuthor(s)http://wendang.chazidian.com

AbstractWorld’slargestmacroalgalblooms(MAB)causedbyUlvaproliferaoutbreakeverysummerintheYellowSeasince2007,whichbringpotentialdamagetoregionalmarineenvironmentandeconomics.Assessingtheevolutionofhistoriceutrophicationstatusisofimportanceforexploringthereasonsfortheblooms.Inthisstudy,weusedanarea-weightednutrientpollutionindex(AWCPI-NP)andoceancolordatatoassesstem-poralchangesineutrophicationstatusintheYellowSeabasin.Resultsshowthatsig-ni?cantshiftsoccurredfromthepre-MABphase(2001–2006)toMABphase(2007–2012):theaverageAWCPI-NPwashigherthanthatinthepre-MABphase(2001–2006)byabout45%;chlorophyllaconcentration,anindicatorofeutrophication,increasedbyabout15%intheregionofMAB.Meanwhile,intheJiangsuShoal,theoriginplaceofthe?oatingmacroalgae,theannualinsitunutrientconcentrationsincreasedrapidlyfrom2000to2011.TheresultobtainedthroughourapproachhighlightsthattheMABintheYellowSeamightbeprimarilylinkedtotheprogressiveeutrophication.Inordertoreducethishazard,policymakersshouldincludethisnewknowledgeforaneffectivecountermeasureplanning.KeywordsMacroalgalbloomsÁWaterqualityÁOceancolorÁSeaWIFSÁMODISÁTheYellow

Sea

&QianguoXingqgxing@http://wendang.chazidian.com

1KeyLaboratoryofCoastalEnvironmentalProcessesandEcologicalRemediation,CAS,

No.17ChunhuiRoad,LaishanDistrict,Yantai264003,China

InstituteofMarineSciences,NationalResearchCouncil,Arsenale-Tesa104,Castello2737/F,30122Venice,Italy2

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1Introduction

Theoccurrenceoflarge-scalemacroalgalblooms(MAB)aroundtheworldarousedaglobalconcernonthecoastalmarineenvironment.Speci?cally,thisMABcausedadverseimpactsonlocalcoastaltourism,marinetransportation,andcommercial?sheries.Coastaleutrophicationisthemostevidentexplanationfortheproliferationofmacroalgaebiomass(SmetacekandZingone2013),althoughtheremightbeotherreasonscontrollingthebloomssuchaslackofgrazerandincreaseinaquaculture(Liuetal.2009).UnderstandingthereasonsforMABisthebasisforacorrectplanofprevention,control,andmitigationactions.

Small-scaleMABoccurredintheYellowSeaatleastsincethesummerof1999(Huetal.2010;Xingetal.2015).However,becauseoftheirlimitedextent,theseeventsneverreceivedpublic’sattentionuntiltheysuddenlypresentedalargescaleof‘‘hazard’’inQingdaointhesummerof2008(Zhangetal.2015),i.e.,whenthecitywasoneofthesiteoftheOlympicGameshenceinthespotlightoftheworld.

SatelliteimagerecordsrevealedthatlargescaleofMABstartedfrom2007intheYellowSea(Keesingetal.2011;Xingetal.2011).These?oatingMABhaveseriouslyimpactedtheYellowSeabycoveringhundredsofsquarekilometersofoceansurfaceineverysummer.IntheearlyMay,i.e.,attheearlystagesofbloom,thepatchesof?oatingalgaeUlvaproliferaoriginatedfromtheturbidwatersofJiangsuShoalusuallydriftsouthwardalongwiththeJiangsuCoastalCurrentandentertheEastChinaSea.AstheNortheastAsiamonsoonbecomesstronger,mostofthe?oatingmacroalgaedriftnorth-wardlyandreachthesoutherncoastofShandongpeninsulainJuneandJuly,andtheydisappearinAugust(Xingetal.2011).Duetotheinsuf?cientknowledgeontheemergingofMABandthereasonsfortheirdevelopment,noeffectivemeasuresaretakenbytheChineseauthoritiestocontroltheblooms,andthesuper?oatingMABoccureverysummerfrom2007,despitethespectacularpresenceinthecoastofQingdaointhesummerof2008.InChina,thestatusofcoastalwatersisregularlymonitoredandrepresentedthroughthecoastalwaterqualitylevels(WQLs)andtheirspatialdistributionintheMarineEnviron-mentalQualityBulletin(agovernmentreport).TheWQLshavebeendominatedbythenutrientpollution,i.e.,thetotalinorganicnitrogen(TIN-N)andtheactivephosphorus(PO4-P)(SOA2010,2011,2013).However,thesitesofregular?eldmonitoringalwayslieinnearshorewaters.Therefore,therearenolongtimeseriesofinsitumeasurementsintheoffshorewaters,andthespatiallydiscreteresultsarenotsuitablefortheenvironmentassessmentatabasinscale.AsreportedbyXingetal.(2010),thereisneitherlong-termdatanoreffectivetraditionalapproachesfortheassessmentofmacroalgae-associatednutrientenrichmentintheentiresemi-enclosedregionofthelargeYellowSeabasin.Chlorophylla(Chl-a),aphytoplanktonpigment,iswidelyusedasindicatorintheassessmentofeutrophication(Carlson1977).Thedynamicsofphytoplanktonisusuallycontrolledbynutrientsinaquaticecosystem(EggeandAksnes1992;GaoandSong2005);similarlyformacroalgae,growthofUlvassp.andEnteromorphaspp.washighlyrelatedtotheenrichmentofnutrient(especiallythenitrogen)asshownbyexperimentalandnu-mericalstudies(Menesguenetal.2006).However,thelong-termrecordsofinsituChl-aarescarcebecauseitisnotacompulsoryparameterinthemarineenvironmentalmonitoringproceduresinChina(Quetal.2006).Alternatively,archivesatellitedatahaveconsiderablepotentialinprovidinghistoricalenvironmentaltrendssincetheyareregularlycollected.Hence,remotesensingtechniquesareoftensuccessfullyusedforassessing123

浒苔;绿潮;2015;海水水质;面积加权水质等级

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marineenvironmentalparameters(Liuetal.2014),especiallyintheoffshorewaterswhereinsitumeasurementsrequireoceanographiccruisesthatarerelativelyfewinnumber.Inordertounderstandthecausesofthepresenceoflarge-scaleMABintheYellowSea,itisessentialtoknowthestatusandthetrendofnutrientenrichmentbeforeandaftertheiroccurrence.Previousstudies(e.g.,Liuetal.2012,2013andtherein)discussedthenutrientpollution;however,theycouldnotindicatehowwasitsevolutionbehindtheMABintheYellowSea.

Inthispaper,weusesatellite-derivedChl-a,seasurfacetemperature(SST),andpho-tosynthesisactiveradiation(PAR)toanalyzethechangeandtrendofeutrophicationintheYellowSea.Inaddition,anovelindexcombiningtheareaofnutrient-pollutedmarinewatersandtheircorrespondinglevelisusedtoevaluatetheentireregionalnutrientpol-lutionstatusofcoastalwatersandtoexploretheprocessofeutrophicationbehindthesuperMAB.

2Dataandmethods

2.1Studiedareaand?eldwork

TheYellowSea(Fig.1a)isasemi-enclosedcoastalseawithanareaof380,000km2connectingtheBohaiSeawithopenwaters—theEastChinaSea;theBohaiSeawithanareaofabout77,000km2mayalsobeconsideredtobepartofthelargeYellowSeaecosystem(UNDP2007).

AsconsequenceoftherapideconomicdevelopmentofChinastartedfromthelastdecades,thecoastalareasoftheYellowSeahaveexperiencedstronganthropogenicimpactbecauseofthenewurbanizationandgrowthofeconomicactivitiessuchasindustry,agriculture,andaquaculture.Coastalanthropizationresultedinlargeamountsofnitrogenandphosphorusaswellasotherpollutantshavebeendischargedintothebasin,and

theFig.1aStudyareaoftheYellowSeaanditsvicinity.Greenarrowsshowthemajordriftingpathwaysof?oatingmacroalgae(Xingetal.2011);thefourredboxesshowthelocationswheresatellite-derivedChl-aconcentrationwasextracted;theredlinesshowthenorthernandsouthernboundariesoftheYellowSea.Thewhitecirclesshowthe?eldobservationsitessampledin2009(15May–19June),andthegreenbulletsindicatethesitesofmacroalgaeobservationonthetidal?ats.bExampleofwaterqualitylevels(WQL)ofChinacoastalwaterqualitylevelsin2007(source:SOA,China)

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aquaticecologicalsystemhasbeenfacingaseriousproblemofdegradation(SOA2010).GreenMABwereinvestigatedbothintidal?atsandinoffshorewaters.In2007,2008,2010,and2014,thelocationofmacroalgaebloomsandtheirtypewererecordedatthecoastofYantai,Qingdao,andtheNorthJiangsuShoal.Thepresenceof?oatinggreenmacroalgaewasdetectedintheoffshorewatersoftheYellowSeaandtheEastChinaSea,duringanoceanographiccruisefromMay15toJune19,2009.ThelocationofstationsisshowninFig.1a.

2.2Area-weightedwaterqualitylevel

Eutrophicationindexorcompositepollutionindex(CPI)canbeusedtoevaluatethepollutionstatusofagivenwaterbody,especiallywiththeissueofeutrophication(Lund1967;SOA2011;Zouetal.1985;Chenetal.2007).CoastalwaterqualityinChinaisdominatedbynutrientpollution(SOA2010,2011,2013),and,inordertoevaluatetheoverallwaterqualitystatusinregionalwaterswhichcanbeclassi?edasdifferentwaterbodieswithdifferentWQLs,anarea-weightednutrientpollutionindex(AWCPI-NP)isproposedinthisstudy(Eq.1):

AWCPI-NP¼5X

i¼2ðNiÁPiÁAiÞð1Þ

whereiistheWQLofpollutedwaters(seeFig.1bforanexampleofChinacoastalWQLsin2007),NiisthelowerlimitofTIN-Nconcentration(mg/L)attheleveli,PithelowerlimitofPO4-Pconcentration(mg/L)attheleveli(Table1),andAiisthecorrespondingareaofwaterbodyatthislevel(km2).WQL(i)anditsarea(Ai)werecollectedfromtheannualreportsofSOA,China,andtheyareavailablefrom2001.TINandPO4-PaswellasothermarineenvironmentalparametersalongChinacoastswereregularlymeasuredonwatersamplesaccordingtoChinastandardmarinesamplingandmeasuringprotocols(GB17378.4-1998)(Quetal.2006;SOA2011).Ateachsite,watersampleswerecollectedatthesurface(0.5mdepth),middle,andbottom(0.5mabovethesea?oor)layers.Theconcentrationofeachparameterwasobtainedbyaveragingthevaluesofthethreelayers.ThesedatawerereprocessedinaregulargridbytheKriginginterpolationmethodforobtainingthemapoftheir2Dhorizontaldistributions.Finally,accordingtothelimitsforenvironmentalparameters,e.g.,TINandPO4-PshowninTable1,theareaofeachlevel

(A)wascalculated.

Asaforesaid,sincethedataofWQL(iandAi)werecollectedinannualreportsbySOAonlyfrom2001,theyearlyAWCPI-NPobtainedbyEq.1referstothe2001–2012period.Inaddition,becausewaterqualitydataofcoastalwatersforYellowSeaandKoreanTable1TINandPO4-PconcentrationsusedforcalculationofAWCPI-NP

Waterqualitylevela

TIN(mgL-1)

PO4-P(mgL-1)

aII0.20.015III0.30.030IV0.40.030V0.50.045WaterqualitylevelsII,III,IV,andVarecorrespondingtorelativelycleanwater,slightlypollutedwater,mediumpollutedwater,andheavilypollutedwater,respectively.And,levelVhasonlyalowerlimitoftheconcentrationofeachpollutant(MEP1997)

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Peninsulaarenotavailable,theAWCPI-NPwascalculatedonthebaseofthewaterqualitydataofChina.Thishasbeendoneonthebasetakingintoaccountpopulation,watershed,andrelatedfactors,andassumingthatAWCPI-NPatthewesternKoreancoastalwaterswouldnotdecrease.Forthisreason,itisreasonabletothinkthisassumptionnotsig-ni?cantlyin?uencedtheresultsoftimeseriesanalysis.

2.3Mapping?oatingmacroalgae

Floatingmacroalgaehavespectralcharacteristicssimilartothoseofvegetation,andthewidelyusednormalizeddifferencevegetationindex(NDVI)orothersimilarindices(ShiandWang2009;Garciaetal.2013)canbeusedtoextractthemacroalgaepatches.Itshouldbenotedthatstudiesusingdifferentspatialresolutionimagesanddifferenceindices(e.g.,Liuetal.2009;Xingetal.2011;Keesingetal.2011;Garciaetal.2013)couldgivedifferentresultsoncoveringareaof?oatingmacroalgae.

Inthiswork,tokeeptheconsistencywithourpreviousresults(e.g.,Liuetal.2009;Xingetal.2011),Moderate-ResolutionImagingSpectroradiometer(MODISterra/aqua)re?ectanceproductswitharesolutionof500mareused.AfterMODISimageriesweregeoreferenced,thebands1#(840–875nm)and2#(620–670nm)wereusedtogeneratetheNDVIimagesandtheNDVIwascalculated(Eq.2).

NDVI=ðband1Àband2Þ=ðband1þband2Þð2Þ

AthresholdvalueofNDVIwassettoidentifythe?oatingmacroalgaepatches;duetotheimpactsfromclouds,haze,sunglints,andwaterbackground,astrategyofdynamicNDVIthresholdwasappliedtoextractmacroalgaepatches(Xingetal.2011;Cuietal.2013).Finally,themaximumMODIS-deriveddailydistributionsofmacroalgaewerecalculatedforthe2007–2013period.

2.4Satellite-deriveddata

TheannualChl-aconcentrationwitha9km99kmspatialresolutionwasobtainedfromthesatelliteimagingproductsofSea-ViewingWideField-of-ViewSensor(SeaWIFS)andMODISaqua(dataavailable:http://oceancolor.gsfc.nasa.gov).TheChl-adatawerederivedfromSeaWiFSandMODISaquaimageryonthebasisofthealgorithmdevelopedbyO’Reillyetal.(1998).Thehighloadofsuspendedsediments,mainlyduetoriverdischargeandsedimentre-suspensioninshallowwatersintheYellowSea,couldleadtooverestimateinsatellite-derivedChl-a(Yamaguchietal.2012).Inordertoreducetheuncertaintiesinanalysis,whichmightbebroughtbytheinaccuratelyestimatedChl-ainturbidwaters,weextractedtheaverageofChl-aatthemiddleoftheYellowSea(123–125°E,34–36°N)aswellastheBohaiSea(120–120.5°E,38.25–38.75°E)consid-eringthe1998–2012period(Fig.1):(a)MODISdata:2002–2012and(b)SeaWIFS:1998–2010.ThesystematicbiasbetweentheSeaWIFSChl-aandtheMODISChl-awascor-rectedwiththeregressionequationbetweenMODISandSeaWiFSmonthlyChl-a(Eq.3).Theywerespatiallyandtemporallymatched,andthen,thecorrectedSeaWIFSChl-afrom1998to2002andtheMODISChl-afrom2003to2012wereusedtogenerateayearlytimeseriesofsatellite-derivedChl-a.

SeaWIFSChl-a;lg/L¼1:0772ÂMODISChl-aþ0:0961ð3Þ

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