Impacts of Nonpoint Source Pollution on Water Quality in the Yuqiao Reservoir

The Yuqiao Reservoir is an important drinking water source for the city of Tianjin. In recent years, the water quality of this reservoir has been seriously threatened by eutrophication resulting from increased nonpoint source pollution loads. In this study, we used a Soil and Water Assessment Tool (SWAT) model to calculate pollution loads (total nitrogen [TN] and total phosphorus [TP]) in the area surrounding the Yuqiao Reservoir. We then established a coupled two-dimensional hydrodynamic and water quality model that was used to simulate temporal and spatial distributions of TN and TP from June to September 2008. SWAT model results provided water quality boundary conditions for the coupled two-dimensional model. Results indicated that Liu Xiangying and Wu Baihu were the main TN inlets, and the average TN concentration in the reservoir was highest in September (3.74 mg/L). Meanwhile, the TP concentration in the eastern portion of the Yuqiao Reservoir was higher than that in the west, and the average TP concentration peaked in August (1.56 mg/L). The combination of the SWAT model and two-dimensional hydrodynamic and water quality model provides an effective method to simulate water pollution with consideration of various factors.