Evolution of nutrient structure and phytoplankton composition in the Jiaozhou Bay ecosystem

The inventories of nutrients in the surface water and large phytoplankton( > 69 microm) were analyzed from the data set of JERS ecological database about a typical coastal waters, the Jiaozhou Bay, China, from 1960s for N, P and from 1980s for Si. By examining long-term changes of nutrient concentration, calculating stoichiometric balance, and comparing diatom composition, Si limitation of diatom production was found to be more possible. The possibility of Si limitation was from 37% in 1980s to 50% in 1990s. Jiaozhou Bay ecosystem is becoming serious eutrophication, with notable increase of NO2-N, NO3-N and NH4-N from 0.1417 micromol/L, 0.5414 micromol/L, 1.7222 micromol/L in 1960s to 0.9551 micromol/L, 3.001 micromol/L, 8.0359 micromol/L in late 1990s respectively and prominent decrease of Si from 4.2614 micromol/L in 1980s to 1.5861 micromol/L in late 1990s; the nutrient structure is controlled by nitrogen; the main limiting nutrient is probably silicon; because of the Si limitation the phytoplankton community structure has changed drastically.