Studies On Biogeochemistry Of Phosphorus In The Coastal Waters Of China

Phosphorus is often the limiting nutrient for algal growth and may limit marine productivity. At present, most studies are focused on dissolved phosphorus concentrations and distributions in our country, and little is known about the suspended paniculate phosphorus and the phosphorus dynamics. In the present dissertation, distributions, partitioning and budget of different forms of phosphorus in the coastal waters of China, i.e. the Yellow Sea and the East China Sea, the Changjiang River Estuaries and the Jiaozhou Bay, are studied detailedly. The main research work is as follows:The different forms of phosphorus are determined during two surveys on the Yellow Sea and the East China Sea in September 2002 and September 2003, respectively. The results show that the distributions of different forms of phosphorus are influenced by Changjiang River diluted water, Kuroshio, Taiwan Warm Current, and Yellow Sea Cold Water, hence the distributions of different forms of phosphorus along different sections are quite variable. The Changjiang River diluted water is the major source of PIP and POP, hence the concentrations of PIP and POP illustrate decrease onshore to offshore, and the sediment brought by Changjiang River has almost deposited in the west of 123° E. The distribution of DIP in the bottom water of section PN, section B and section A and YT are influenced by the Kuroshio Intermediate Water, Taiwan Warm Current and Yellow Sea Cold Water, respectively. At the junction of different water column, the vertical exchange and upwelling there brought amount of nutrients for phytoplankton reproduction, hence the concentrations of DOP are relatively high there.The influence of tide to distribution of phosphorus can be observed at station El,E2, E3 and E5. The concentrations of DIP are maximum at the ebb and are minimum at the flood, the concentrations of PIP and POP are maximum at the flood and are minimum at the ebb. At E4 station, the PIP and POP were governed by settling/resuspension induced by the cyclic changes of tidal currents in September, 2002, and were controlled by dilution of outer water in September, 2003.The Kuroshio Water is the most major source of DIP to the East China Sea, which accounts for 73% of the total DIP source. The Kuroshio Water and Yellow Sea contribute about 41% of total DOP source to the East China Sea, respectively. The Yellow Sea contribute 39% of total PP source. The Shelf Surface Water is the most major sink of phosphorus, almost in dissolved form. In the East China Sea, about 69.6 + 31.9X 109 mol of phosphorus are assimilated by plankton annually, in which about 88% of the phosphorus assimilated by plankton is recycled in the water column.The different forms of phosphorus are determined during four surveys on the Changjiang River Estuaries and its adjacent areas in October and November 2002 and February and May 2003, respectively. The results show that the Changjiang River diluted water is the major source of DIP, PIP and POP, hence high concentrations of DIP, PIP and POP are observed at the Changjiang River Estuaries. The DOP has highest concentration at (123 ° E, 30.5 ° N), which was consistent with the distribution of diatom cell density. In the coastal area(west of 122.5° E), PP are the dominate form of phosphorus.The solid-solution partitioning of phosphorus can be quantified using the conditional distribution coefficient, Kd. The Lg (Kd) has highest value in Spring, followed by Summer, Autumn and Winter. The DIP brought by the Changjiang River are almost depleted, reach 89%~97%.The Changjiang is the major source of phosphorus to the East China Sea. In the Changjiang River Estuaries and its adjacent areas, about 33.9+17.9 k ton of phosphorus are assimilated by plankton annually, in which about 70.2% of the phosphorus assimilated by plankton is recycled in the water column.The different forms of phosphorus are determined during seven surveys in the Jiaozhou Bay from October 2001 to May 2003. The results show that theconcentrations of different forms of phosphorus decreased seaward expect DOP, which had the peak value in the central. The contribution of PP to TP in the west part of Jiaozhou Bay is 1.5-2.4 folds higher than that the east part of the Jiaozhou Bay. During a tidal cycle, PIP and POP were significantly cyclic between flood and ebb governed by settling/resuspension induced by the tidal currents. There were obviously seasonal variation for different forms of phosphorus, and DIP, DOP and POP was well correlated with the biomass of phytoplankton. The DIP depletion percent values are calculated for five major rivers, which empting into the Jiaozhou Bay. The riverine DIP concentration is the key factor controlling the percent of estuarine DIP depletion. The rivers are the major source of phosphorus to the Jiaozhou Bay, contribute about 62% of total phosphorus source. In the Jiaozhou Bay, about 961.0 + 98 ton of phosphorus are assimilated by plankton annually, in which about 95% of the phosphorus assimilated by plankton is recycled in the water column.