Changes of the environmental parameters and their relationship in recent twenty years in the Bohai Sea

Abstract

The series data of nutrients and biological parameters in the central Bohai Sea for 20 years were reviewed. It is found that both concentration and relative content of nutrients were 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 average ratio of N/P in May and October in the central Bohai Sea was increased from 1 64 in 1982～1983 to 16 2 in 1998～1999, but the average ratio of Si/N was decreased from 13 12 in 1982～1983 to 1 32 in 1998～1999. The situation of nitrogen limiting in the central Bohai Sea was gradually changing to that of relative lack of phosphate and silicate. The decrease of Yellow River flow into to Bohai Sea may be resulted in this change. These may limit the growth of diatom and thus promote the development of pyrrophyta if other conditions (e.g.temperature and hydrodynamics) were suitable. This may be the major factor for pyrrophyta red tide occued in Bohai Sea.