L-thia Based Research On Temporal-spatial Evolution Of The Non-point Source Pollution In Nansi Lake Basin

At present, the non-point source pollution(NPS) is the main factor of the Nansi Lake water environment. It is the premise and basis to master the temporal and spatial distribution characteristics for controlling non-point source pollution. This research analyst the space-time evolution features of land using/cover changes in Nansi Lake Basin, correct key parameters inside the L-THIA model, simulate the temporal and spatial distribution characteristics of rainfall runoff and NPS pollutant load(COD, and TN and TP) in Nansi Lake Basin, analyst the impacts of land use type and rainfall change on non-point source pollution in-depth, and put forward the corresponding measures.The main contents and conclusions are as follows:(1) Using Landsat TM and ETM images as data source. The land use maps of years 2000, 2005 and 2010 were obtained by the method of supervised and artificial interpretation. The dominant land use types of Nansi Lake Basin were cultivated land and construction land, In 2010, the areas of cultivated land and construction land were 19611.7 km2 and 4840.8 km2, occupying 67.7% and 16.7%, respectively. In the past 10 years, the overall change in land use expressed an increase in construction land, woodland, water and wetland, and the reduction of cultivated land, grassland and unused land. During 2000-2010, cultivated land reduced by 748.96km2 and 3.68%, and construction land increased by 689.8 km2 and 16.6%.(2) Compare the average annual runoff with simulated rainfall runoff based on L-THIA model of 3 sub-basin in Nansi Lake Basin, the relative errors are all below 10%, related coefficient(r) are greater than 95%; and Nash-Sutcliffe coefficient are between 0.30 to 0.36; The non-point source pollution loads(COD, and TN and TP) errors in this research are 2.1%, 2% and-8.8% compared with predecessors simulation results based on L-THIA model.(3)In 2010, the discharge intensities of COD, TN and TP in Nansi Lake Basin were 89.8 kg/ha, 38.5 kg/ha and 2.2 kg/ha, respectively. The NPS pollution loads of Nansi Lake Basin were mainly from construction land and cultivated land, and the pollution loads of COD, TN and TP from both land use types in 2010 took up 99.0%, 99.0% and 98.8 %, respectively. During 2000-2010, COD, TN and TP increased 8801.6 t, 180.3t and 71.9 t, non-point source pollution has become the most important factors affecting the water quality in Nansi Lake Basin.(4) The land use type and precipitation is the main factors of the space-time difference of non-point source pollution in Nansi Lake Basin. The construction land has a higher output of pollutants,leading to non-point source pollution load increases. And precipitation is the driving force of non-point source pollution, during one year,the non-point source pollution which mainly concentrated in the 6-9 months is in trend line with precipitation changes.