Effects Of Land Use Structure On Nitrogen Export At Watershed Level

South-North Water Transfer Project is one of large-scale strategic projects of trans-basin water resouces allocation in China's economic constraction.It's building in have great significance to alleviate the grim situation on lack of water resources in North China plain.Danjiankou reservoir have a stringent requirement in water quality as largest drinking water source protection area,at the same time,the proteion of water quality is the key of South-North Water Transfer Project.Nitrogen pollution is being in Dnajiangkou reservoir,in order to provide a theoretical basis for control and management measures of NPS in Danjiangkou reservoir,this paper study the effect of land use stuctre on nitrogen export base on the dates of land use and nitrogen expoxt in Danjiangkou reservoir,the main results are as follows:(1)Analyzeing land use structure of Hujiashan watershed,the rusult shows,"source" land use is the main in watershed,the ration of dry land and residents up to 52.79%,The highest of ration of dry land and residents in Wulongchi sub-watershed,that ration up to 78.62%.and lots of"source" land use distribute in distance of 30m sides river,"sink" land use distribute 50m away from river.Besides,lots of dry land distribute the slop of >25°.(2) Analyzeing the nitrogen export from Jan.to Dec.in 2008,result shows that, nitrate nitrogen was the main compoment in nitrogen,NO₃^--N/TN up to 50%.Total nitrogen export highest in spring,higher in summer and autumn and lower in winter, nitrate nitogen export highest in autumn,higher in summer and spring and lower in winter. The coefficient of variation of spatial is winter autumn summer spring,the nitrogen export concentration of all sub-watershed exceed theâ…¡standards of urface water environmental quality standards.(3)Analyzeing the effect of land use on NO₃^--N/TN,the result shows that,relativity of NO₃^--N/TN and residential than relativity of NO₃^--N/TN and dry land.woodland and grassland have a negative correlation to NO₃^--N/TN.Annually,residential was the top nitrogen producer.However,seasonally,top producers were dry land,residential, residential and dry land in spring,summer,autumn and winter,respectively. (4) The results showed that dry land and residential area exported significant amount of nitrogen,whilst forest and grassland could be considered as nitrogen sinks.Land use was a controlling factor that determined the amount of nitrogen export,although the effects varied with time.Annually,dry land was the top nitrogen producer.However, seasonally,top producers were dry land,residential,residential and dry land in spring, summer,autumn and winter,respectively.Rainfall,temperature and human activity are also important for influencing the nitrogen export.(5) Analysis the relation of land use and temporal and spatial coefficient of variation of total nitrogen,the result show that season and land use structure effect on coefficient of variation of space of total nitrogen and nitrate nitrogen together.Negatively correlation between dry land,residents and nitrogen together,positively correlation between woodland,grassland and nitrogen together.(6)Basis on the research of effect of land use patterns on nitrogen export,found that land use patterns and nitrogen export has a certain relevance.Unreasonable land use pattern of nitrogen is the majior cause of pollution caused,so that,adjusting and optimizeing the land use pattern and making use of land I reason are essential requirement for control soil erosion and non-piont source pollution.