[Historical evolvement trends of nutrients in waters of Bohai Bay from 1985 to 2003].

The local condition and the historical evolvement trend of nutrient elements were studied by the collection and analysis of the local investigation and the historical data. The surface seawaters are under the bad nitrogen contaminative conditions. Beitang and Dagu estuary are the main contaminative sources of inorganic nitrogen and phosphorus. The historical evolvement trend of DIN and DIP has close correlation with the yearly runoff, especially in the coastal areas near Dagu estuary. The remarkable positive correlationship between DIN, DIP and the yearly runoff indicates that the main pollution emission source of nutrient elements is the exogenous discharge input. The nutrients structures have changed greatly from 1985 to 2003. Nitrogen limiting in 1985 has changed into phosphorus limiting in 2003, which will influence the structure of phytoplanktons in Bohai Bay.