Research On Non-point Source Pollution Control In Nansi Lake Basin Based On The Theory Of "source-sink" Landscape Pattern

As the largest freshwater lake in northern China,the water quality of the Nansi Lake Basin is related to the quality of the south-to-north water diversion and domestic water.In recent years,sewage discharge,excessive use of chemical fertilizers and pesticides have aggravated the non-point source pollution in the Nansi Lake Basin.Since non-point source pollution is affected by the spatial arrangement and combination of different landscape types,in order to control non-point source pollution,this paper based on the "source-sink" landscape pattern theory,analyzes the landscape structure characteristics,spatial and temporal changes of the Nansi Lake Basin based Landsat TM data and DEM data from the 2010 to 2015.Nitrogen and phosphorus weights were assigned to different landscape types by combining statistical data and spatial attribute data,Landscape Contrast Index(LCI)and The Grid source-sink Landscape contrast Index(mGLCI)were analyzed by ArcGIS,so as to study the spatial and temporal changes and characteristics of the contribution of "source-sink" landscape pattern to non-point source pollution risk of ford.Through the reasonable distribution of "source" and "sink" landscape layout,the non-point source pollution can be balanced in the time and space process,and the final goal of controlling the non-point source pollution can be achieved.The main conclusions are as follows:(1)The construction land and cultivated land in the Nansi Lake Basin changed obviously,and the cultivated land was occupied mainly by the construction land.The analysis of spatial and temporal landscape types of the Nansi Lake Basin in 2010 and2015 found that the main landscape types the Nansi Lake Basin are cultivated land,forest land,grassland,wetland,construction land and bare land.Among them,the construction land and cultivated land have the largest change,and there is mutual transformation between them.The landscape distribution is significantly affected by slope and relative elevation.With the increase of slope and elevation,the proportion of cultivated land and construction land decreases,while that of forest land and grassland increases.Below 100 m in elevation,plain is the main landscape type,and cultivated land is the main landscape type.(2)The analysis results of Landscape Contrast Index show that the unreasonable distribution of "source-sink" landscape pattern in the Nansi Lake Basin is gettingworse,and the unreasonable distribution of such water systems as the Guangfu River,Zhuzhao New River,Dongyu River,and Wanfu River basin is more serious than other water systems.In 2010 and 2015,the LCI values of N,P and NP were all greater than0 in slope,relative height and distance,with an upward trend.Meanwhile,the risk of nitrogen pollution was higher than that of phosphorus pollution.The basin area of more than 1000 km2 of large rivers in LCI index analysis,The LCI values of the 7rivers are all greater than 0,and the N and P for LCI values of the Guangfu River basin more than 0.40.The unreasonable distribution of the "source" and "sink" landscapes along the river is more serious.then the landscape structure of Zhuzhao New River,Dongyu River,and Wanfu River basin also need to adjust.(3)Based on ArcGIS,An analysis of The Grid source-sink Landscape contrast Index shows that the area of the source has been increasing,the area of sinks has been decreasing,and the unreasonable distribution of landscape is aggravating over the past five years.In plain areas where construction land is concentrated,m GLCI values are generally high.As the distance from the lake body approaches,mGLCI values tend to increase.On the north bank of the Nanyang Lake,the west bank of the Zhaoyang Lake and the west bank of the Dushan Lake,the imbalance of "source" and "sink" landscapes is the most serious.In the mountainous and hilly areas in the east of the basin,because of the increase in slope and elevation,the distribution of the forest land,grassland and other landscapes is concentrated,and the mGLCI value is small.(4)Based on the calculation and spatial analysis of the Landscape Contrast Index,the measures and suggestions for landscape optimization are put forward.By adjusting the landscape type and combination mode,the key areas are identified,and the risk of non-point source pollution is controlled.This article divides the Nansi Lake Basin into four major areas according to the reasonable combination of landscape,the risk of non-point source pollution to the lake,the local terrain and economic characteristics,and related policies,including the key ecological protection zone of the river basin,the ecological protection zone and buffer zone at the river source,the lake ecological protection area,scenic area ecological protection area,and carries out regional landscape adjustment and environmental governance in different regions.