土地利用变化对绿洲区地下水硝酸盐空间变异特征的影响

Effects of Land Use Change on the Spatial Variation Characteristics of Nitrate Content in Groundwater in Oases

应用遥感、地理信息系统和地统计学方法,分析了三工河流域绿洲区地下水硝酸盐空间变异特征和土地利用/土地覆被变化状况,探讨了土地利用变化对绿洲地下水硝酸盐空间变异特征的影响。研究数据主要包括2004年77口采样井地下水水质数据以及1987年TM影像和2004年ETM影像数据。结果表明,流域上游至下游硝酸盐含量逐渐降低,样点含量介于1.4～83.1mg·L-1之间,变异系数为1.11,属于较高的变异强度。上游冲洪积扇和下游冲积平原硝酸盐平均含量分别为27.37和6.02mg·L-1,冲洪积扇出现了显著的地下水硝酸盐污染。硝酸盐含量较高的区域均是土地资源开发历时较长的区域,主要为耕地和建设及工矿用地的土地利用变化方式。反映出随着绿洲的不断扩展,土地利用变化对地下水硝酸盐空间变异特征产生了显著的影响。

The spatial variation characteristics of nitrate content in groundwater and the situation of land use/cover change in the oasis in the Sangong River Basin, Xinjiang, are analyzed, and the effects of land use change on the spatial variation characteristics of nitrate content in groundwater are lucubrated using RS and GIS means and geostatistical methods. The data used in the study include mainly the data of groundwater quality measured from 77 wells in 2004, TM image in 1987 and ETM image in 2004. The results reveal that the nitrate content in groundwater varies in a range of 1.4-83.1 mg·L^-1, the variation coefficient is 1.11, and the variation intensity is high. The nitrate content in groundwater decreases gradually from the upper reaches to the lower reaches of the drainage basin, the average nitrate contents in groundwater beneath the alluvial-diluvial fans in the upper reaches and beneath the alluvial plain in the lower reaches are 27.37 mg·L^-1 and 6.02 mg·L^-1 respectively, and groundwater beneath the alluvial-diluvial fans is significantly polluted by nitrate. The nitrate content in 27.3% groundwater samples in the study area is higher than the health standard of potable water in China（20 mg·L^-1）, and that in 40.3% groundwater sampies is higher than the health standard of potable water of World Health Organization（ 10 mg·L^-1 ）. There is a high spatial correlation of nitrate content in groundwater （17.9%）, and the spatial autocorrelation distance is 32 kin. These reveal that the spatial heterogeneity of nitrate content in groundwater is mainly caused by the spatial structure, such as the terrain, landforms, hydrological conditions and soil, the soil structure and the hydrological cycle process are changed by land use change, and human activities, such as urban construction, agricultural reclamarion, cropping pattern and irrigation and drainage intensity, affect significantly the spatial variation of nitrate content in groundwater. The areas where the nitrate content in groundwater is high are the regions with long-term exploitation of land resources, and the land use patterns are dominated by farmlands and lands for construction, industrial and mineral purposes. Groundwater beneath the alluvial-diluvial fans in the upper reaches, where the old oases are developed, is seriously polluted by nitrate due to the extension of urban areas and long-term cultivation, and the pollution sources are mainly the application of agricultural chemicals, sewage irrigation and drainage of urban waste water and domestic sewage. The alluvial plain in the lower reaches is the main part of the newly reclaimed farmlands ; however, groundwater beneath the plain will be possibly polluted by nitrate if the irrational exploitation of land and water resources is Continued. Therefore, the irrational human activities and the irrational exploitation of land and water resources must be restricted so as to improve groundwater quality, avoid groundwater pollution, conserve the oasis environment and achieve sustainable development in the drainage basin.