Effect Of Land Use Structure On Non-point Source Nitrogen Loss In Typical Small Watershed,China

South-North Water Transfer Project is one of large-scale strategic projects of trans-basin water resource’s allocation in china’s economic construction.It’s building in have great signification to alleviate the grim situation on lack of water resources in North China plain.Danjiangkou reservoir have a stringent requirement in water quality as largest drinking water source protection area.In order to improve the situation of non-point source pollution in reservoir area,The local government implemented a comprehensive renovation project of the river basin,which is based on the reform of the slope,The implementation of the project changed the situation of land use in the reservoir area,Land use is the key factor of non-point source pollution,the combination of land use type and structure has an important influence on non-point source pollution.Taking Hujiashan small watershed as the study area,based on the monitoring data of runoff plots with different slope and different land use types,the output coefficient of non-point source nitrogen in different land use types was estimated,under the support of GIS technology,our study explored the effect of small watershed management project on temporal and spatial variation of TN load of non-point source pollution,in order to reveal the influence of comprehensive control project on the spatial and temporal variation of watershed non-point source pollution and provide a theoretical basis for control and management measures of non-point source in Danjiangkou reservoir.The main results are as follows:Analyzing land use structure of Hujiashan watershed,the results shows,the implementation of comprehensive control project increased the area of cultivated land,reduced the area of woodland and wasteland.The cultivated land is mainly distributed in the slope range below 15 degrees,the trend was gradually reduced with the increase of slope in 2005,but showed a trend of first increase and then decrease in 2015.Before the project implementation,the distribution of woodland less below 8 degrees interval,by 2015 the area increased significantly,however,Woodland area in the range of 15 degrees above the proportion is far lower than before the implementation.The area of wasteland was reduced in all the slope range,especially in the following 15 degrees interval in 2015.The inflow and outflow of land use types are different in different slope ranges.Cultivated land mainly changed into forest land,forest land changed into cultivated land and wasteland changed into cultivated land and forest land below 8 degrees interval.Cultivated land and forest land are relatively stable in 8~15° interval。A large number of cultivated land inflow,but woodland and wasteland outflow in 25~35°interval.Large amounts of cultivated land continue to flow,a large number of forest outflow,compared with other areas of badland,the gap between the inflow and outflow rate narrowed.In 2015,the output load of TN was reduced by 25.6% compared with that in 2005.The contribution rate of cultivated land to non-point source TN output was significantly higher than that of other land use types,before and after the implementation of governance projects were 54.1% and 57.9%,respectively.The high nitrogen load intensity area mainly concentrated in 5 ~15°interval,but concentrated at 15 ~35°interval after the implementation of the project.The output of non-point source TN load caused by land use change in 2015 decreased by 2827.91 kg compared with that in 2005 in whole watershed.The increase of cultivated land area plays a decisive role in the increase of TN load output,the increase of forestland and wasteland area had little effect on the increase of TN load in 2005~2015.The increase of cultivated land TN load mainly comes from the conversion of forest land to cultivated land.The contribution of wasteland to farmland was mainly in the range of 8~15°and 15~25°interval,the contribution of other areas was smaller than that of TN.The contribution of forest land to TN load was mainly from the conversion of cultivated land to forest land,the conversion of wasteland to woodland contributes less to TN.The increase of TN load caused by forest land conversion was mainly above 15°interval.