Impact Study Of Land Use On Water Quality In Reservoir Basin

Water resource is the key factor to ensure the sustainable development of the society.In recent years,due to the change of land cover caused by land urbanization and the severe non-point source pollution caused by excessive fertilization,water quality has become a trend of deterioration.As an important factor affecting hydrological processes and water quality,land use change will not only lead to changes in vegetation types and landscape patterns,but also further affect the process of surface water circulation,which will have a certain impact on water quality.Therefore,in-depth analysis of the impact of land use on hydrology and water quality in the study area can not only clarify the characteristics of non-point source pollution in the study area,but also contribute to land use optimization and water resources protection in the future.Taking the upstream basin of Tangpu reservoir as the research area,the study analyzes the land use characteristics in 2009 and 2019,and evaluates the water quality of water quality monitoring point in the basin by using a variety of evaluation methods.Besides,the study simulates the nitrogen and phosphorus output of the basin in 2015-2019 by using SWAT model,and analyzes the influence of different land use composition and landscape pattern index on the nitrogen and phosphorus output.The study explores the change trend of nitrogen and phosphorus load under different scenarios.The main conclusions of this study are as follows:(1)From 2009 to 2019,the land use change of the basin was mainly due to the decrease of cultivated land and forest,while the increase of construction land.The overall landscape characteristics of the basin showed a trend of increasing fragmentation and complex landscape.The overall land use intensity of the basin increased,and the local land use intensity was mainly low and middle,and there was spatial autocorrelation.In 2029,the area of cropland,garden and water in basin will decrease,and the area of construction land will increase rapidly.(2)The results of single factor evaluation showed that the total nitrogen of water quality exceeded the standard seriously.The overall Nemerow pollution index was slightly higher than 1,which belonged to the light pollution level.The change range of the comprehensive nutritional status index was small,and belonged to the grade of medium nutritional status basically,but there is a trendency to eutrophication.(3)From 2015 to 2019,the annual average total nitrogen output in the Tangpu Reservoir Basin was 317.66 t,and the annual average total phosphorus output was48.69 t.The nitrogen and phosphorus output in the reach of the basin was higher in the main river channel,but lower in the tributaries.The average total nitrogen output per unit area of sub-basins was 6.39kg/hm2,and the total phosphorus output was1.99kg/hm2.The high nitrogen and phosphorus output values were mainly in subbasins No.4、10、12、15 and 22.(4)The annual average per unit area output of total nitrogen in cultivated and garden land were large,17.76kg/hm2 and 21.58kg/hm2 respectively,while the total phosphorus output which was 5.06kg/hm2 was large in cultivated land,indicating that cultivated and garden land contributed more to the nitrogen and phosphorus output.From the perspective of the relationship between land use type proportion and nitrogen、phosphorus output,the proportion of cultivated and construction land was positively correlated with nitrogen and phosphorus output,while the proportion of forest was negatively correlated with it.The results showed that the water quality of subbasins dominated by forest was better than that dominated by cultivated and construction land.(5)Landscape indices such as IJI,SPLIT,SHDI and DIVISION were positively correlated with nitrogen and phosphorus output,while LPI and CONTAG were negatively correlated.The results showed that the better the landscape integrity and connectivity,the smaller the degree of fragmentation and human interference,the more conducive to reduce the output of nitrogen and phosphorus,and play a role in protecting water quality.In addition,the study also show that reducing the amount of chemical fertilizer,riparian vegetation filter zone and returning farmland to forest can help to reduce the output of nitrogen and phosphorus.