Analysis of general additive model on the relationships between chlorophyll-a concentrations and environmental factors in Beihu Lake of Chongming Island.

The relationships between chlorophyll-a and its related environmental factors in Beihu lake was studied by GAM method. The total phosphorus, total nitrogen and water temperature were significant as explanatory variables in explaining chlorophyll-a (P0.05). Chlorophyll-a initially increased monotonically with the total phosphorus, but decreased monotonically after the total phosphorus reached 0.12mg/L. Impacts of different total nitrogen concentrations on chlorophyll-a varied, being weak when the total nitrogen concentration ranged from 0.6 to 1.8mg/L. Highest chlorophyll-a concentrations occurred when the water temperature ranged from 24 to 26℃. Furthermore, the relationship between chlorophyll-a and the TN:TP ratio was significant (P0.1) nonlinear relationship. Chlorophyll-a was inversely related to TN:TP ratio under nitrogen-limitation. Chlorophyll-a decreased monotonically with TN:TP ratio under phosphorus-limitation.