Abstract:

The rapid increase of nonpoint source pollution has made water quality of Le′an River decline in recent years.Water samples were taken in April,September and December 2009,and land use investigation was carried out in Le′an River watershed for nonpoint source nitrogen pollution study.Using GIS as a tool,spatial information was analyzed to demonstrate the temporal and spatial characteristics of nonpoint source nitrogen pollution of the study area.Results indicated that loss of nitrogen was mainly via the soluble form.TN and DTN changed rapidly throughout the year.Generally,they were highest in December,followed in April,and lowest in September.The range of TN concentration was 0.09~1.359mg/L,indicating that Le′an River was reaching to mediumeutrophication situation.The average concentration of NO3－N was 65% of DTN.NO3－N was the major form of DTN loss and had similar spatial and temporal distribution with TN.The average concentration of NH3－N was the highest among the forms of nitrogen in September.NO2－N concentration was the lowest throughout the year.The research area was divided into two districts according to the physiognomy and the terrain:the northeast low mountains and the southwest hilly area.Various forms of nitrogen concentration in southwestern part were generally higher than those in the northeastern,and the water quality of the upstream was generally better than the downstream