A PHOSPHORUS-PHYTOPLANKTON DYNAMICS MODEL FOR LAKE DONGHU IN WUHAN

An eutrophication model has been developed for Lake Donghu in Wuhan, an eutrophic shallow body of water with a hydraulic retention time of about five months. The model describes the growth of phytoplankton and phosphorus cycling in the lake on 1-year time scale, and the state variables in the model are phytoplankton biomass, phosphorus in algal cells, orthophosphate, phosphorus in detritus and phosphorus in sediment. The results of model calibration and verification showed that the deerministic description of the given state of the ecosystem by the model is satisfactory, and the model can reasonably respond to the changes of forcing functions in the ecosystem. According to the tentative ideas about the recovery of the lake from eutrophication by engineering techniques, the model has been used to make the forecasts of water quality before and after diversion of the waste water for the lake and to examine the effects of sediment removal or lake water replacement on the improvement of the water quality. The various predictions given by the model are believed to be useful to map out a desirable programme for the restoration of the lake.