Simulation on stream flow and nutrient loadings in Gucheng Lake, Low Yangtze River Basin, based on SWAT model

A distributed watershed hydrologic model soil and water assessment tool (SWAT, 2000 Version) was applied to simulate stream flow and nutrient loadings (including total nitrogen (TN) and total phosphorus (TP)) in Gucheng Lake Basin, which is located in the lower reach of Yangtze River Basin. Model parameters related to stream flow and nutrient loadings were calibrated and validated by the observed value, and the simulation showed that the simulated values were reasonably comparable to the observed data, suggesting the validity of SWAT model. The simulated surface runoff and nutrient yield between two stages, viz. 1981–2000 and 1951–1960, were compared, basically considering land reclamation in the mid-1970s. The result indicated that, the average annual runoff and output of TN and TP in 1981–2000 were 1.32 × 108 m3 a−1, 411.88 × 103 kg a−1 and 43.04 × 103 kg a−1 respectively, much higher than that in 1951–1960, which were 1.15 × 108 m3 a−1, 49.55 × 103 kg a−1 and 7.67 × 103 kg a−1 respectively. The simulation provides better understanding on stream flow and nutrient loadings responding to variations of land use conditions, agricultural tillage operation and natural rainfall, etc.