Abstract：Based on the monitoring data on water quantity and quality at different river cross sections, a procedure on calculating the spatial distribution of pollutant loads was suggested. A method for identifying critical source area based on the relationship between pollutant loads and catchment areas in sub-areas was further proposed. The procedure and method had been taken into practice in the Jinjiang River Basin, an important drinking water source area. The results showed that the output pollutant loads of the Jinjiang River Basin (Jinji water intake section) mainly derived from East stream (EStm) and West stream (WStm). In low river flow periods, the output pollutant loads of CODMn, NH3-N (ammonia nitrogen) and TP (total phosphorus) were 226.8, 27.1 and 17.1g/s, which accounted for 18%~67% of high and normal flow periods. In high and low flow periods, EStm (Honglai section above) and WStm (Yuanmei section above) had almost same contribution in pollutant loads to the total outputs, but in normal flow period WStm generated significantly greater pollutant loads than EStm. Five critical source areas were indentified using the above method, including Penghu-Changtingqiao, Changtingqiao-Ganglong and Hengkou-Yuanmei section, etc. The identification method can not only mirror spatial distribution of pollutant concentrations and loads, but also define key pollutants and sensitive flow periods, which is beneficial to pollution control. The proposed procedure and method in this paper can be widely used in the other river basins in China.
