Temporal and Spatial Variation of Water Pollution in Zhegao River of Chao Lake Basin

Spatial and temporal variation of water pollution of Zhegao river,a tributary of Chao lake,was studied based on the one-day field survey and sampling along the river and the monthly sampling at the outlet of the river during a period of four years.The results demonstrated that water quality of the upper part of the river was at the level Ⅱ-Ⅲ,according to the surface water quality standard,but the nutrient concentration attained moderately eutrophic status with the main nutrient source from agricultural fields;the middle part of the river,which flows through the Zhegao town and receives un-treated municipal effluent,was very seriously polluted,with water quality varying between Ⅴ and inferior Ⅴ and being in hypereutrophic status.The water quality of the main river and its tributaries in the downstream part was at the level Ⅲ-Ⅴ and was at eutrophic status,with multiple pollution sources,such as upstream flow,domestic and agricultural input,inner river sources.Water quality at the outlet showed obvious seasonality: Nitrate level was higher in winter-spring period than in summer period,while total phosphorus(TP) was on the country with higher TP levels in summer,which was a big threat for the river and its receiving water: Chao lake.Multiple control and management measures should be taken to improve the water quality of Zhegao river.