Characteristics of eutrophication and variation trend of nitrogen and phosphorus nutrient in Shenzhen bay

Based on the field data in 1986-2007 in Shenzhen bay, annual changes characteristics of nitrogen and phosphate concentrations, as well as their correlations with each other are presented. Furthermore, the Nutrition Quality Index (NQI) is employed to assess the eutrophication degree of Shenzhen bay. The dissolved inorganic nitrogen(DIN) concentration shows an increasing trend, while phosphate(PO43--P) concentrations decrease gradually. Ammonia nitrogen (NH4+-N) is the primary form of inorganic nitrogen in Shenzhen bay indicating that inorganic nitrogen is in unstable thermodynamic equilibrium. The ratio of DIN/P increased gradually before 1998, and decreased after 2002. The variation and components of nutrients could influence the community structure of phytoplankton, and the dominant red tide species have been transformed from diatom to dinoflagellate. Nutrient correlation is significant at the 0.01 level, which shows that the nutrient undergo similar biogeochemistry processes. The NQI shows that Shenzhen bay is in high eutrophic status, and it is urgent resort to effective plan for controlling water pollution in the inflow river.