The Distribution And Variation Of Dissolved Carbon And Nitrogen In The East China Sea

The East China Sea is a model with various characteristics of marginal seas,which has attracted more and more attention for harmful algal blooms. Carbon andnitrogen are all basic elements for growth of plankton. The research onbiogeochemical characteristics of carbon and nitrogen in the sea, can help us discussthe mechanism of harmful algal blooms, and plays an important role for estimatingthe flux of carbon dioxide between gas and marginal sea.Seawater samples were collected from statins nearby the Changjiang Estuaryduring April and May, included9cruises, and analyzed for dissolved organiccarbon（DOC）, dissolved organic nitrogen（DON）, and dissolved inorganiccarbon（DIC）, in combination with hydrophical, chemical and biological dates, weanalyse the distribution and influence factors of them. The C/N is also related. Themain results are following:The concentration of DOC is higher near the shore than offshore in investigatingarea. During the bloom, the distribution of DOC is related to the quantity of plankton,and irregular in the surface and middle waters. DOC is affected by terrestrial inputsand biological activities simultaneously. The concentration of DOC is inverselycorrelated with salinity indicates the distributions of DOC is influenced by theterrestrial inputs. DOC in the bottom water is inversely correlated with AOU. Whenthe phytoplankton bloom breaks out, the distributions of DOC is positive correlatedwith chlorophyll, which indicates the distribution and concentration of DOC arerelated to the biological activities.The distribution of DIC in the area is higher near shore and lower offshore. Theconcentration of DIC near the shore is mainly affected by terrestrial inputs andtemperature. Through the analysis of the relevance between DIC and temperature, orsalty, we can find that DIC is influenced by the terrestrial inputs and temperature inspring, and temperature play a more important role. Phytoplankton absorbs CO₂andrelease as organic carbon, which can affect the distribution and concentration of DOCand DIC. Because of the phytoplankton bloom, DIC is quite influenced by thebiological activities in May, and chlorophyll is inversely significant correlated withDIC.According to the distribution characteristics of DIC, we could find that the pCO₂is high in the terrestrial inputs, which conducts as the source of the CO₂. Because theproductivity of Kuroshio Current is low, the pCO₂is high by comparison. Theconcentration of HCO₃-is higher with the depth increasing of the sea. Theconcentration of CO₃2-is higher in the surface and lower in the bottom, becausePhytoplankton absorbs CO₂in the surface, while bacteria decompose organiccompound and release CO₂in the bottom.The distribution of DON is higher near shore and lower offshore, whichindicates it is mainly controlled by the terrestrial inputs. The distribution of the DON is related to the biological activities, because the concentration of the DON was highin the area where the phytoplankton bloom broke out. From April to the middle ofMay, with strengthen of the biological activities, the proportion of the DON to theTDN increases gradual, which indicates the biological activities affects thetransformation of the nitrogen. In late May, because the decreasing of the terrestrialinputs and Kuroshio Current with low DON, the average concentration of the DONbecome lower. Terrestrial input was the main resource of the DON, because theconcentration of the DON was inversely correlated with the salty. As a whole, maybebecause of the great influence of the terrestrial input, the relationship between DONand chlorophyll was weak, but in the area with large quantity of plankton, theconcentration of DON is high. The C/N is smaller near shore and larger offshore.When phytoplankton bloom broke out, the C/N becomes smaller in accord with thevalue of the Redfield ratio.The concentration and distribution of DOC、DIC and DON in the water isanalyzed, the tendency of the C and N agrees well with process of the phytoplanktonbloom during the investigation. Though the terrestrial inputs and the quantity ofplankton is uncertain, investigation in the small-scale could not describe the wholeregularity of the C and N accurately.We use Hierarchical cluster analysis divide thedates into three groups, including: the basic elements of phytoplankton, the hydrologyand biological parameters related to the biological activities, and the hydrologicparameter which indicates the influence of terrestrial inputs.