Analysis of water environmental pollution in plain river network region in small watershed of Caoqiao River

As the main inflow river in the Taihu Lake Basin, Caoqiao River Basin is a typical plain river network in small watershed region, which owns a gentle topography, lots of small rivers around. Pollution sources and pollutants characteristics were analyzed by source apportionment for the basin. The results showed that chemical oxygen demand(COD) mostly came from industrial and rural life pollution, as for total nitrogen(TN), mainly from agriculture farming and dry-wet deposition, NH4-N, mostly from dry-wet deposition, agriculture farming, industrial and rural pollution; total phosphorus(TP), mainly from agriculture farming and urban life pollution. Water pollution index of four water quality monitoring sections were evaluated and analyzed, and the results showed that the water quality reached water standard Ⅳ during high-flow period, and was inferior to water standard V during mean and low flow period. In addition, water quality of upper reaches could be affected by inflow from Wuyi Canal, while lower reaches by inflow from Taige Canal. There were thirty-seven major rivers around Caoqiao River being evaluated by equivalent standard pollutant loading method, which showed that the total nitrogen loading was the largest, followed by ammonia. This research can provide basis in water regulation of Caoqiao River basin network and eco-restoration planning of water environment, and also provides a certain reference for water regulation of river network area in the south of China as well.