Search

Abstract: The Changjiang (Yangtze River) is known to contribute significantly to the eutrophication that has caused drastic changes to the ecosystem of the East China Sea. However, evidence for historical changes in nutrient concentrations and composition and the consequent effects on the ecosystem in the coastal water is sparse. In this paper we present some long-term data for nutrient concentrations and Si:N:P ratios in the freshwater and the river plume and the long-term response of the ecosystem structure in the river plume. These data reveal increases in the dissolved inorganic nitrogen and phosphate concentrations in the Changjiang freshwater by a factor of five from the1960s to the end of the 1990s and a reduction in dissolved silicate by two thirds over the same period. Concomitantly, an increase in DIN concentration and a reduction in silicate concentration both by a factor of two were observed in the surface water of the Changjiang plume. As an ecological consequence to such nutrient changes, the chlorophyll a concentration increased by a factor of four since the 1980s and harmful algal blooms increased rapidly since 1985 in the Changjiang estuary and adjacent sea areas. The macrozoobenthic biomass decreased sharply from the mid 1980s to the present, suggesting that the Changjiang estuary has been in a high eutrophication state since that time. We predict that, due to the continuously increasing nutrient pressure, the symptoms of eutrophication associated with nutrients will worsen in the Changjiang plume in the near future. [Copyright &y& Elsevier]

This paper discusses the distributions of micronutrients in the Yellow Sea (YS) and the East China Sea (ECS), based on the data obtained during field observations. It is pointed out that there are abundant nutrients in the area of the east and northeast of the Changjiang River estuary throughout the year. It is believed that the nutrients come from the extension of the Changjiang River diluted water and the transportation of the Subei coastal water. The maximum extension range of the nutrients of the Changjiang River diluted water was observed during the catastrophic flooding period of the Changjiang River in the summer of 1998. Based on the Redfield ratio (Si:N:P = 16:16:1) at which three essential nutrients are utilized by marine phytoplankton, the Si/N/P ratios are calculated and studied for the upper water of the YS and the ECS. The results indicate that the Si/N ratios are very high, which suggests that silicate is not the limiting factor for the growth of phytoplankton in the YS and the ECS. Under the influence of terrestrial runoff, especially the Changjiang River runoff which is rich in combined nitrogen and has very high N/P ratios, high N/P ratios occur in the Changjiang estuary and its adjacent areas such as the south and southwest of the YS, the inshore area of the ECS and the area east of the Changjiang estuary in spring and summer. As a result, in contrast to general open marine systems, the systems in these areas resemble estuarine ones rather than typical marine ones. The primary production in a considerable portion of the YS and the ECS may be limited by phosphate rather than nitrogen. [Copyright &y& Elsevier]