Study on Load of Nonpoint Source Pollution in the Second Songhua River Basin

Nonpoint source pollution (NPS) has been considering as a major environmental issue around the world. It is much more difficult to identify and control nonpoint source than point source (PS). This study was designed to estimate the loads of chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) in the Second Songhua River Basin, where the hydrometeorological characters had distinguishingly seasonal wave and NPS pollution loads were mostly produced in the flood season. PS pollution was much more readily identifiable and its load was steady during a year and interannual years. On the basis of the long term real-time monitoring data of flow and river water quality in the con- trol section (Ganshuigang Section), which was located in the watershed outlet, the loads of NPS and PS could be estimated. The result showed that mean pollution loads of COD from NPS and PS in 1985—2006 were 99 930 t·a-1,174 743 t·a-1, which accounted for 36% and 64% of to- tal output load, respectively. NH3-N load of NPS was 9 888 t·a-1, which occupied 44% and grew markedly during the last five years. PS was still greater pollution source in the research basin. There were significant positive correlation relationship between NPS load and flow, obvious temporal and spatial fluctuations of NPS pollution load in the river basin. The model of NPS load (y) for COD and the flow (x) was y=-44 849+ 161.682x by using regression analysis method. Therefore, it was indispensable to dispose waste water from industrial and municipal sections and to control NPS from farmland runoff in order to protect water quality in the basin. Also, the study provide an useful method to forewarn NPS pollution loads by forecasting of precipitation and flow mass, which will afford a scientific and practical tool of watershed management and NPS pollution control in the Second Songhua River Basin.