Sedimentary records of eutrophication in the Changjiang Estuary upwelling area over last 100 a

TheupwellingareaintheChangjiangEstuarywasselectedtocollectthecore,wheretheredtideoccurredfrequentlyandhypoxicexisted.Thetotalorganiccarbon(TOC),totalnitrogen(TN),biogenicsilica(BSi)andstableorganiccarbonisotopicratios(δ13Corg)weredeterminedonthe210Pb-datedsedimentcore.TheconcentrationsofTOC,TN,BSiaswellastheirsedimentationfluxeshaveincreasedtosomeextentsincethe1970s.TOCandTNfluxesincreasedabout45%,36%respectively.Theaverageδ13Corgvalueinthecorewas-23.67×10-3whichremainednearlyconstantbeforethe20century.Theδ13Corgvaluesincreasedafterthe1900s,twomarkedincreaseswereobservedfromthe1950sandthe1970s.Asimpleδ13Corgmodelwasusedtoestimatethecontributionofterrigenousandmarineorganicmatterinputsforthesediment,whichindicatedtheincreaseinaccumulationsincethe1970shasbeenalmostexclusivelymarine.Theincreasingofmarineorganicmatteraccumulation(TOC,TNandBSi)wascorrespondingwiththeincreasingoffertilizerconsumptionandtheNO3-NbudgetsfromtheChangjiangRiver.Theriverinerunoffoffertilizersandnutrientsstimulatedthealgaeblooming.Enhancedprimaryproductionresultedinanenrichmentoforganicmatterinthesediment.ThesedatasupportthehypothesisthatanthropogenicnutrientloadinghasbeenasignificantfactorontheeutrophicationintheChangjiangEstuary.