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Sedimentary Records Of Changing Structures Of Phytoplankton Communities For The Last Hundred Years In The Changjiang Estuary

Posted on:2010-11-09Degree:DoctorType:Dissertation
Country:ChinaCandidate:H Y JinFull Text:PDF
GTID:1100360302479563Subject:Environmental Science
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Particulate organic carbon and photosynthesis pigments were investigated to know the characteristics of organic carbon and the structure of the phytoplankton communities in Changjiang Estuary and East China Sea.Then the paleoproductivity and the changing environment conditions in the past 60 years were discussed based on the studies of some proxies such as organic carbon and nitrogen with their stable isotopes,biological silicon,chlorin and photosynthesis pigments of surface sediments and a sediment core.The results indicate that the primary production is high in the inshore water with high nutrient levels(N/P>16,displays as potential P limits sea area),and the phytoplankton communities derived by HPLC photosynthetic pigments dominated by diatom,next as the cryptophytes,chlorophytes,prymnesiophytes,dinoflagellate and cyanobacteria,but no chrysophytes and prochlorophytes in summer along the latitude of 31°N in East China Sea.While in the outside continental shelf sea area,with low nutrient levels and obvious nitrogen limitation,the primary production was low,and the phytoplankton was dominated by cyanobacteria in the surface water,next as the crysophyes,prymnesiophytes,chlorophytes and prochlorophytes.The diatom was few in the surface water while in the bottom there was some,indicated outward lateral transport.Most of cyanobacteria degraded during deposition in the water column and only a few can deposited in the sedimens.The concentrate of particulate organic carbon was high near the shore affected by the contents of suspended particles while it decreased outwards in the East China Sea.POC in surface layer sea water mainly originates from the marine organisms,while the detritus organic carbon contributes greatly in the bottom layer,especially in inshore water.The contents of total organic carbon(TOC),biological silicon(BSi) and chlorin were used as "proxies" for paleoproductivity.The contents of TOC ranged from 0.10 %to 0.72%in surface sediments with high values in the inner shore and low values off shore.The terrestrial inputs in the Changjiang Estuary and Hangzhou Bay affected the use of TOC as the proxy of paleoproductivity.BSi mainly performance for diatom's productive forces,and the contents ranged from 0.05%to 0.30%.Diatom productive displayed high in the inshore which reduced to the open sea.Chlorin attribute to marine phytoplankton productive forces,the contents is 0.03μg/g~7.71μg/g,the high value distributes in the area of 122.5°E~123.5°E,corresponds with the high productive forces area in the Changjiang Estuary.Studies of Organic carbon isotope(δ13Corg),Nitrogen isotope(δ15N) and the Corg/N ratio indicate thatδ13Corg information was relatively appropriate for difference the originate of organic matters in study area.δ13Corg ranged from -24.45‰to -20.48‰,indicates the mixing source of organic matter from terrestrial origin and marine organisms.δ15N value demonstrates the information of biogeochemistry process transformation.δ15N was light as a result of nitrogen fixation influence in the outshelf of East China Sea,but the inshore water depositδ15N was the result of synthesis information of the nitrate surplus,selectivity degradation of organic matter and denitrification transformation process.Corg/N ratio was changed from 5.27 to 11.29 in study area,reflect the organic matter originates in certain degree,but affected by the absorbance of NH4+ as well as organic matter selectivity degradation.Stable organic carbon isotope,biogenic silicate and pigments were studied from a sedimentary core for discussing the variation of paleoproductivity and the environmental implications in the past decades in Changjiang Estuary.The sedimentary rate was 1.55±0.03 cm/a and the core had recorded the information from the beginning of 1940s to 1997.The sedimentary organic carbon was mixing originate derived from the signature ofδ13Corg(-19.50‰~-26.15‰) and Corg/N values (4.03~19.4).The changing value ofδ13Corg indicated that the riverine organic carbon increased after 1980s..δ15N was 2.23‰~6.39‰,demonstrates the information of biogeochemistry process transformation.Lowδ15N value in the middle of the core, corresponds with the time of 60s~80s was affected by the increasing nitrate inputs and increasing nitrogen fixation.The biogenic proxies present three stages of paleoproductivity changes:Before 1950s,Marine primary production was low,and it increased during 1950s-1980s with diatoms dominated,consistent with increasing of nutrients concentrations.Chlorophytes and cyanobacteria were increased either in this stage.Then the production decreased Later than 1980s.In this stage,the diatom production decreased while the production of other phytoplankton communities such as prasinophytes,crysophytes or dinoflagellate increased.It was affected by continually inputs of high nitrate,but Si,P and so on assume reduce the tendency,and it results high N/P,P/Si nutrients ratios in changjiang Estuary.
Keywords/Search Tags:Organic carbon/nitrogen stable isotope, photosynthetic pigments, paleoproductivity, phytoplankton communities, Changjiang Estuary, East China Sea
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