城郊农业区小流域土地利用结构对氮素输出的影响

以位于湖南省长沙市城郊农业区的金脱河流域为研究区域,通过解译2009年的Spot-5卫星遥感图获取了小流域的土地利用图;结合流域的DEM图,利用ArcGIS 9.3的水文、空间分析模块将流域划分为若干个子流域,分析各子流域的土地利用结构.从2009年12月～2010年11月在各子流域出口处采取水样,分析其TN、NH4+-N、NO3--N输出浓度、输出量的时空变化特征以及与土地利用结构、施肥等因素之间的关系.结果表明,流域径流氮素污染严重,其TN、NH4+-N输出浓度呈明显的季节变化特征,为冬季>春季>夏、秋季,而NO3--N的输出浓度的季节差异较小.流域内的土地利用结构对NO3--N的输出浓度起着重要的控制作用,林地、水面表现为源作用,水田、旱地、居民地为汇作用;不同的时间尺度上土地利用结构对其影响不同,年度尺度上对NO3--N输出影响最大的为旱地,春夏季为林地,秋冬季为旱地.TN、NH4+-N的输出浓度与土地利用结构的相关性较差,各形态氮素的输出量与纯氮施用量、人口数、养猪量表现为极显著正相关.

Influence of Land Use Structure on Nitrogen Output in the Watershed of Suburban Agriculture Regions

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.