Analysis Of Ultrophication Variation Characteristic And Ecological Effect Of Bohai Sea

With the rapid development in Bohai Sea Area, the environmental quality of Bohai Sea is not so optimistic. Ultrophication and frequent redtide have bcome serious ecological problems. As an important sustaining system, the healthiness of Bohai ecological environment plays an important role for the economy healthy development in Bohai Bay area. So Systematically analysis the variation character of Bohai ultrophication and the relation with redtide has an important significance for making a further research on ecological environmental evolutive mechanism, openning out environment quality variation trend and prevention and cure of environment pollution of Bohai Sea. These conclusions are as follows:(1)At the early stage of 1960's, DIN concentration in Bohai Sea water has a very low background value, otherwise the concentration of PO4-P has a relative high background. Since 1980's, the concentration of DIN and PO4-P increased rapidly and reached the peak value in 1995 and 1997, respectively . Then the concentration of DIN and PO4-P showed decreasing trend. This variation trend is closely related to. the development of agriculture and industry around the Bohai Sea, the amount of nitrogenous fertilizer utilization, restricted P in consumer goods (especially for scour), as well as the pollutants control. During fifty years, concentration of SiO3-Si continous decreased, which illustrate the less fresh water entering into the Bohai Sea. DIN/PO4-P increase and SiO3-Si/DIN decrease gradually.(2)The plane distribution of DIN,PO4-P,COD in surface sea water shows a decreasing trend from coastal area to middle area. Especially at the four rivermouth area and the coastal sea area of some important coastal cities, their concentration is higher than annual average value.(3)Since the late stage of 1980's, ultrophication is the main factor for the increasement of redtide occurrence. High concentration of nutrious salts is the main reason for the frequent redtide at the bottom of Bohai Bay and Liaodong Bay. High sea water temperature, enough high DIN and PO4-P concentration in coastal sea area and more and more nutrious salts discharging from land-based sources which is much more for the phytoplankton actural requirement are the most important reasons for the redtide occurring in summer in Bohai Sea. In the Lvjuhe rviermouth sea area, utrious salts, sea water temperature and salinity are the main factors which influence redtide in summer in 2004.