Spatial Characteristics Of Non-point Source Pollution And Its Effects On Water Quality In The Hanfeng Lake Basin

Agricultural non-point source pollution?NSP?plays an important role in water quality deterioriation and eutrophication,and has been the focus of scientific research and hot issues for a long time.Hanfeng Lake is located at the north shore of Kaizhou District,Chongqing City,and simultaneously situated at the end of Xiaojiang River connected to the backwater area of Three Gorges Reservoir.It is an artificial lake that was used to reduce the effects of the Three Gorges Reservoir riparian zone on the ecological environment of Kaizhou District.Hanfeng Lake has various types of landscape and wetland resources and thus plays a very unique role in ecological and economic status in the Three Gorges Reservoir Area?TGRA?.Clarifying the spatial charateristics of NSP and interpreting its effects on the water quality of Hanfeng Lake are of great significance for understanding the change charateristics of TGRA and making the rational water management measures.In this study,the contribution and spatial distribution of various agricultural non-point pollution sources were mastered in Hanfeng Lake Basin.And,14 sampling points were set up in the inflow,lake and effluent areas of Hanfeng Lake.In the each later month in 2015,water samples were collected and the main water quality indicators were analyzed.Cluster and principal component analysis techiques were used to analyze the temporal and spatial variation characteristics of water quality in Hanfeng Lake,and to study the impact of non-point source pollution on the water quality of Hanfeng Lake.The main results are as follows:?1?According to the types of NSP,the main NSP sources in Hanfeng Lake Basin were fertilizer application,livestock and poultry breeding,crop straw and rural life emissions.The contribution of fertilizer application to TN and TP was 2112.12 t and374.71 t,respectively.The contribution of livestock and poultry breeding to TN and TP was 535.05 t and 108.59 t,respectively.The contribution of crop straw to TN and TP was 70.8 t and 8.37t,respectively.The contribution of rural life emissions to TN and TP was 0.35t and 0.04t,respectively.The contribution of non-point source pollution load caused by fertilizer application accounted for77.61%and 76.16%of the total,followed by that of livestock and poultry industry,accounting for 19.66%and 22.07%of TN and TP,respectively.The NSP caused by fertilizer application was the most serious.?2?In terms of spatial distribution of NSP,the total load of agricultural non-point source pollution for TN and TP in Hanfeng Lake basin is 2721.42 and 492.04t,respectively.The contribution rates of TN in Taoxi River basin,Nanhezi River basin,Donghezi River basin and Hanfeng Lake sub-basin are 28%,35%,31%and 6%respectively,and the contribution rates to TP are 26%,34%,35%and 5%,respectively.The Nanhezi watershed has the highest contribution rate to TN,while the Donghezi watershed has the highest contribution rate to TP.The intensity of TN load is0.2756t·hm^-2,0.325 t·hm^-2,0.328 t·hm^-2 and 0.424 t·hm^-2,and the output intensity of TP is0.047 t·hm^-2,0.057 t·hm^-2,0.066 t·hm^-2 and 0.0612 t·hm^-2,respectively.The output intensity of TN and TP is the highest in Hanfeng Lake Basin and the lowest in Taoxi River Basin.?3?The water quality monitoring points of Hanfeng lake basin can be divided into4 areas respectively,based on the cluster analysis,including the water intake area of Nanhe river and Donghe River,the upper reaches of Hanfeng Lake and the middle and lower reaches of Hanfeng Lake.The concentrations of TN,TP and NH₄⁺-N,in the tributaries were significantly higher than those in Hanfeng Lake.Principal component analysis showed that the main nutrient sources:COD_Mn?TN?NH₄⁺-N?NO₃^--N?TP?DP?PO₄^3--P?Chl-a of Hanfeng Lake are Taoxi River Basin in the Nanhe River inflow area and the upper reaches of Donghe River inflow area,which is consistent with the results of NSP load analysis.