Influence of Land Use Structure on Nitrogen Output in the Watershed of Suburban Agriculture Regions
城郊农业区小流域土地利用结构对氮素输出的影响

This study was conducted in Jintuo watershed of Changsha City,Hunan Province,in the suburban agriculture regions,by selecting 8 sub-basins to examine the effect of land use on watershed runoff nitrogen output.The land use map of watershed was interpreted from Spot-5 image of 2009,and by using hydraulic analysis function and spatial analysis extensions of ArcGIS 9.3,the catchment areas were delineated from DEM.Water sampling was carried out from Dec.2009 to Nov.2010,and the relationships between different types of nitrogen export and land use were analyzed.The results showed that nitrogen pollution in the watershed was extremely serious.There was a distinct seasonal variation in the following order: WI>SP>SU ≈ FA in the output concentration of total nitrogen and ammonium nitrogen which was not observed in the nitrate output.Moreover,land use was a dominant factor that determined the export of nitrogen,and especially a significant correlation was figured out between the nitrate output concentration and the land use structure.Forest and water body had a negative impact on nitrate output concentration while dry land,paddy field and habitation road had a positive effect.However,the effects varied with time.Dry land had the most significant important effect on nitrate output concentration in winter and fall,but in spring and summer was the forest land.The correlation between land use structure and the output concentration of total nitrogen and ammonium nitrogen was not found.The resident number,pig number and fertilization also had a major impact on nitrogen output quantity.