Nutrients concentration and changes in decade-scale in the central Bohai Sea

The nutrients contents and distributions are discussed briefly, based on the data obtained in 1998~1999.Besides explanation of the results, a 20-a time series data of nutrients and biological parameters for central Bohai Sea are reviewed.It is found that both concentration and relative content of nutrients have been changed dramatically.The increase of nitrogen and decrease of phosphate and silicate led to the dramatically increase of N/P ratio and the decrease of Si/N ratio.The situation of nitrogen limiting in central Bohai Sea is gradually changing to that of relative lack of phosphate and silicate The decrease of the Huanghe River input to the Bohai Sea may be responsible for this change.These in turn may limit the growth of diatom and thus promote the development of pyrrophyta if other conditions (e.g.temperature and hydrodynamics) are suitable.We conclude that this may be the major inducement factor of pyrrophyta red tide in the Bohai Sea.