Modeling of water quality evolution and response with the hydrological regime changes in Poyang Lake

The water quality in Poyang Lake has changed in recent 20 years according to the long-term data analysis. The main driving factors of water quality evolution trends are the increasing pollutant loads and hydrological regime alterations. The water levels in the lake have declined, which led to the shortening of the limnetic faces period of the lake. The seasonal allocations of basin inflow and lake outflow have also been altered mildly by some hydraulic facilities in the basin. To study the impacts of changing hydrological regime on water quality, a two-dimensional depth-averaged model for hydrodynamics and water quality is set up, validated, and applied to simulate two hydrological processes before and after Three Gorges Reservoir as 1956-2002 and 2003-2015 scenarios. The results reveal that water quality in lake are mainly determined by the pollutant loads and are influenced by the hydrological regime particularly in spring and autumn. The hydrological regime changes of Poyang Lake have resulted in 10.6 and 11.7% increases in TN concentrations associate with 12.4 and 13.6% increases in TP concentrations during the periods of April-May and September-October.