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 (530KB)
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65,458,000 Yen (FY1998: 26,993,000 Yen)
In order to understand the effect of the Changjiang River on the marine environment and the marine ecosystem in the East China Sea, an investigation was conducted offshore from the Changjiang River in October 1997 and May 1998. Temperature and salinity distributions were used to understand the structure of the water mass. It was shown that the Changjiang water plume (below 300100 salinity) flows in the surface layer (less than 10 m depth) and reaches as far as long 123¼£E in autumn and long 124¼£E in spring. Nutrient distribution was used to understand nutrient supply from the river. The N/P atomic ratio in the coastal area was as high as 32 in autumn and 47 in spring, which indicates that there is an excess of nitrogen supplied from the river. The dominant phytoplankton species in autumn (diatoms) were different from those in spring (dinoflagellates). The reason for this was not depletion of silicate in spring, but other factors (stratification of water, N/P ratio, etc.). In order to examine the possible input of anthropogenic heavy metals from the river, the elemental compositions of suspended particles were analyzed; the main sources of 26 elemnents in the suspended particles were soil particles or plankton, Nutrient concentrations in the pore water of bottom sediments were analyzed to estimate what quantity of nutrients can be released from the sediment to the water column. PO43- concentrations in pore water were 4 to 30 times higher than that of the water column, indicating that PO43- can be supplied to the water by disturbance of bottom sediments, which is strongest in winter.
Changjiang estuary, Nutrient, Phytoplankton, Suspended particles