| The Danjiang River Basin originates from the southern slope of the Qinling Mountains.The soil layer is thin and easy to be eroded,and the area of the slope farmland is large,accounting for 65%of the total cultivated land area.The soil nutrient loss in slope farmland is serious,and the main pollution form in Danjiang River Basin is agricultural non-point source pollution.Based on GIS and RS technology,this paper discusses the response relationship between vegetation pattern,land use pattern and agricultural non-point source pollution.Through the research on water quality,vegetation and land use,the paper analyzes the status of water polluti,on in Danjiang,reveals the change law of Danjiang vegetation,and inverts the vegetation coverage of Danjiang River;analyzes the temporal and spatial changes of land use,and simulates 2020 and 2030.Land use will eventually lead to a non-point source and landscape response.The main conclusions of this study are as follows:(1)The overall water quality of Danjiang River Basin is good,but the contribution rate of total phosphorus and ammonia nitrogen to agricultural non-point source pollution is higher,which has a greater pollution risk.In terms of inter-annual variation,the water quality of Danjiang River Basin changed steadily and seasonal variation was not obvious,but the difference of dissolved oxygen was obvious:winter>spring>autumn>summer,microbial reproduction in summer directly affected the decrease of dissolved oxygen in water;82.14%of 84 monitoring in 7 years were in a clean state,and 16.67%were in a slight pollution state.And the pollution of Danjiang River Basin is mainly agricultural non-point source pollution of total phosphorus and ammonia nitrogen type.(2)The vegetation in the Danjiang River Basin has recovered well.The annual average NDVI of the basin showed fluctuations,and finally stabilized around 0.71;the seasonal variation of NDVI showed "arch shape",which has a high similarity with the trend of precipitation;it will show positive and sustained growth in the future;estimate the vegetation coverage of Danjiang River Basin.Degrees show that the average coverage of Danjiang in 2002 and 2015 is 60.3%and 71.2%respectively;the characteristics of vegetation landscape:medium and low coverage is more fragmented,reflecting the strong influence of human activities,the decrease of dominance and richness;Extremely high coverage tends to be more integrated,with increased dominance and richness.(3)The urbanization of land use in Danjiang is accelerating obviously.Grassland is the base landscape of the study area,and grassland area>forest area>cultivated land area>urban area>water area>unused land area;the fastest growth rate of land use is the cities and towns from 2005 to 2013,with the change rate reaching 4.465%,and the fastest decrease is the cultivated land from 2000 to 2005 with the change rate of-0.785%.The land use in 2030 is simulated,compared with 2010,cities and woodlands.The land use landscape characteristics of the study area:fragmentation of the region,reduction of richness and dominant species,poor landscape extensibility and connectivity,but more landscape contact and diversity.(4)Agricultural non-point sources and land use in Danjiang River Basin have a better response relationship.In the order of correlation degree between agricultural non-point source pollutants and vegetation landscape,ammonia nitrogen>total phosphorus>total nitrogen>nitrate nitrogen,and agricultural non-point source and land use landscape all have correlation degree:ammonia nitrogen>total phosphorus>nitrate nitrogen>total nitrogen,but they all have good correlation degree;establish the response relationship between agricultural non-point source pollutants and vegetation landscape,agricultural non-point source pollutants and land use landscape,and establish multiple factors.Regression model,and through introducing vegetation coverage index to optimize the regression model of total phosphorus and landscape pattern,and achieved good results,finally four regression models of agricultural non-point source pollutants were determined.Land use in 2030 was simulated by calculation,and then the spatial and temporal changes of non-point source pollution in Danjiang River Basin were estimated.It was concluded that the source of Danjiang River would still be calculated under the evolution of land use.It is a "serious disaster area" of agricultural non-point source,and the total nitrogen pollution is the most serious.According to the characteristics of Danjiang River Basin,the strategies of ecological conservation in the upper reaches,ecological development in the middle reaches and ecological restoration in the lower reaches are put forward. |
