| In the dissertation, temporal- spatial variability for the carbon fixed production of phytoplankton (CFP) and its role playing in carbon cycle in the South Yellow Sea (SYS) as well as the response of ecosystem were discussed in detail for the first time. The annual value of CFP in the entire marginal seas of eastern China and their contribution to the absorption of atmospheric CO2 were also gained. Furthermore, simulated experiments coupled with ocean biota dynamics were performed in laboratory. In these experiments, effects of pollutants on marine carbon fixation system and CO2 fluxes were investigated. A series of results and viewpoint are presented as followed:1. The CFP of the SYS in recent years were characterized of distinguished spatial and temporal change which was significantly correlated with phosphate concentration, light availability and chemical hydrographic condition. It had significant influence on the carbon sink/source pattern in the SYS. The value of CFP was estimated to be 9.5×104t d-1 in 2005 and found to show a negative trend since 1983 which should mainly attribute to the deficiency of phosphorus in the SYS through our analysis. The annual value of carbon fixed production of phytoplankton in the entire marginal seas of eastern China was estimated to be 222×106t, which accounted for 2% of the annual value of CFP in global marginal sea areas. Carbon fixation system of phytoplankton was examined for its biogeochemical activities based on the compositive investigations of hydrography, chemistry and biology in the SYS. The value CFP in autumn of the SYS ranged from 97 to 701 mg C m-2 d-1 with an average of 307 mg C m-2 d-1. Study showed that the correlated factors to CFP were transparency, salinity, pH, ammonia, phosphate and Chl a. Among these factors, the most correlated was phosphate which was controlling factors to phytoplankton growth in autumn of the SYS, and the second was Chl a and ammonia.Investigation showed that if excluding data gained from the stations occupied by upwelling (A9,B7,B8,B9,C8,C9,D9和A1), a good negative correlation (r=-0.8,n=23, p<0.001)between CFP and pCO2 of the surface water would be found. In the eastern region of the SYS where the CFP value was relatively high, pCO2 was low; however, in the western region of the SYS where the CFP value was relatively low, pCO2 was high. The average value of CFP corresponding to the transition from CO2 source area to CO2 sink area was 230 mgC m-2 d-1, namely while CFP lower than this transition, the corresponding sea area was presented as a source to atmospheric CO2. By contrast the sea area became a CO2 sink area. It showed that carbon fixation of phytoplankton had significant influence on the carbon sink/source pattern in the SYS. Furthermore, according to the present study results together with previous investigations, the annual value of carbon fixed production of phytoplankton in the entire marginal seas of eastern China was estimated to be 222×106t, which accounted for 2% of the annual value of carbon fixed production of phytoplankton in global marginal sea areas. Besides, it was as 16.2 times as the annual value of apparent carbon sink strength (1396×104t) in the entire marginal seas of eastern China.The study of spatio-temporal mechanism of CFP showed that from 1999-2005 the CFP in the costal waters has been positively related to transparency. Since 2001 the CFP in the central region of the SYS has been positively related to phosphate concentration with a reasonably good correlation but had lack of correlation with TN concentration, which indicated that SYS ecosystem has probably been experiencing limitation of P rather than N. The factors correlated to CFP in the YS and ECS mixed Water were relatively complicated than in other water types. It was controlled by light availability and nutrients supplement simultaneously in such water type.Moreover, we found that there were pronounced responses of ecosystem to the changes of the water quality parameters in the SYS during observation years, including strengthening nutrient limitation, declining Chl.a and phytoplankton abundance, succession of dominant phytoplankton species from diatoms to non-diatoms and zooplankton biomass, especially the negative trends of CFP (decrease from 536.52 mgC m-2 d-1 to 353.02 mgC m-2 d-1). It means that the role of the SYS playing in the process of photosynthesis carbon fixation has declined. Furthermore, zooplankton abundance and fish production were also declined during the observation years.2. Simulated experiments coupled with ocean biota dynamics were performed in laboratory and the changes of marine biological carbon fixation system and CO2 sink/source pattern under the stress of heavy metal (copper, cadmium, zinc and lead) and organic pollutants (ethanol, acetone, organic nitrogen and organic phosphorus) were investigated. The results indicated that changes of carbon fixation system and CO2 sink/source pattern were correlated with the concentrations and kinds of pollutant. In the groups of low concentration of pollutant (0.1and1μmol L-1 for heavy metal , <0.5 mol L-1and <75 mol L-1 for ethanol and acetone, respectively), the dry weight of alga and carbon fixation strength of marine biological carbon fixation system were increased and DIC,HCO3-and Pco2 significantly decreased comparing to the control experiment data (P<0.01), correspondingly. However, when the pollutant infusions were higher than the"critical concentration", the carbon fixation strength were decreased and organic carbon might change into inorganic carbon. As a result the concentration of DIC,HCO3-and Pco2 were ascended and the ascending range was correlated with the kind and dose of pollutant. As for organic nitrogen (ON) and organic phosphorus (OP), when they were 80 and 20mgL-1, decreasing trend of inorganic carbon in sea water was still found. It showed that nitrogen and phosphorus in the pollutant could be used by alga as nutrient source and promoted carbon fixation.Moreover, the results indicated that CO2 sink/source pattern might be controlled by pollutant and were correlated with the concentrations and kinds of pollutant. The critical concentration was 5μmol L-1for copper, 20μmol L-1for cadmium and 0.75mol L-1for acetone, respectively. when the pollutant infusions were lower than that critical concentration, the corresponding sea water was presented as a sink to atmospheric CO2 and when the pollutant infusions were higher than that critical concentration, the sea water became a CO2 source area. For the other pollutant, in the range of our experiment dose, the sea water was always present as an atmospheric CO2 sink.
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