GIS and L-THIA Based Analysis on Variations of Non-point Pollution in Nansi Lake Basin,China

Non-point source(NPS) pollution is the main threat to regional water quality,and the estimation of NPS pollution load has become an important task for NPS pollution control in China.Combined with geographical information system(CIS),the longterm hydrologic impact assessment(L-THIA) model was used to evaluate the temporal-spatial changes of chemical oxygen demand(COD),total nitrogen(TN) and total phosphorus(TP) in Nansi Lake basin from 2000 to 2010.The results show:1) the estimated COD,TN and TP loads in 2010 are260017.5,111607.7 and 6372.0 t with the relative errors of 2.1%,2.0%and-8.8%respectively,and more than 90%concentrated in the raining period from June to September;2) cultivated land and construction land take up more than 80%of the whole Nansi Lake basin,and the proportions of the three kinds of NPS pollution loads coming from cultivated land and construction land are more than 98%;3) during 2000-2010,the COD,TN and TP loads increase by 8801.6,180.3 and 71.9 t respectively,and become the main impact factors on the water quality of Nansi Lake.