新疆三工河流域绿洲地下水水质空间变异特征分析

Characteristics of Spatial Variations in Groundwater Quality of Arid Oases over the Sangong River Basin in Xinjiang,China

本文以新疆三工河流域绿洲为研究区域,覆盖全流域选取了77个样点进行实地采样及地下水水质化验分析,运用GIS的地统计分析方法对水质数据进行半变异函数模型分析,揭示了干旱区绿洲地下水水质空间变异性特征。研究结果表明,整个绿洲地下水矿化度、Cl-离子、HCO-3离子和硫酸盐具有中等的空间相关性,硝酸盐具有较强的空间相关性;冲洪积扇绿洲地下水化学特征以NO-3-SO2-4-Ca-Mg型为主,矿化度通常<800mg/l,地下水硝酸盐含量较高,局部地区已造成了地下水硝酸盐污染;冲积平原绿洲地下水化学特征以SO2-4-CL--HCO-3-Ca-Na-K-Mg型为主,矿化度通常>1000mg/l,局部地区矿化度含量较高,主要以硫酸盐、氯化物为主。

Development and evolution of oases in arid areas rely largely on groundwater resources. The unbalanced relationship between water resources and land use is an essential reason for oasis desertification and vegetation degeneration over arid areas. The heterogeneity in spatial distribution of water resources is one of primary constraints affecting long-term exploitation and utilization of water and land resources for arid areas. The characteristics of spatial variations in groundwater quality and the situation of land use/cover changes in the oases of the Sangong River basin, Xinjiang, were examined by means of remote sensing and GIS techniques and associated geostatistical methods. Measurements of groundwater quality from 77 wells over the study area and Landsat ETM ＋ imagery in 2004 were utilized. Results indicated that there exist a kind of moderate spatial correlation between mineralization, CI-, HCO3-, and SO4^2- ion, and a high degree of spatial correlation between mineralization, Cl-, HCO3-, and nitrate content in groundwater. The spatial heterogeneity in nitrate content in groundwater was mainly caused by the spatial structure and its composition, such as terrain, landforms, hydrological conditions and soil. Soil structure and hydrological processes were generally changed by land use/cover changes and human activities, like urban construction, agricultural reclamation, cropping pattern, irrigation and drainage density, which significantly affected the spatial variations in nitrate content in groundwater. The hydrochemical characteristics in alluvial-diluvial fans in the upper reaches of the river were predominantly represented by NO3.-SO4^2--Ca-Mg, with showing the mineralization of groundwater generally lower than 800 mg/1. The areas with high nitrate content in groundwater, like farmland, land for construction, industry and mining, have been undergoing a long period of land resource exploitation and utilization. The hydrochemical type was SO4^2- CL-- HCO3--Ca-Na- K-Mg over the alluvial plain in the lower reaches of the river, with showing the mineralization of groundwater usually higher than 1000 mg/1. The groundwater quality in some regions have become more and more deteriorative, which was closely related to over-exploitation of land resources, irrigation and drainage activities, increasing surface evaporation and the use of chemical fertilization. Groundwater in the alluvial-diluvial fans in the upper reaches of the river, where old oases had been developed, was significantly polluted by nitrate due to urban sprawl and long-term cultivation. The pollution sources were mainly from the applications and utilizations of agricultural chemicals, sewage irrigation, drainage of urban waste water and domestic sewage. Newly reclaimed farmland prevails over the alluvial plain in the lower reaches of the river; however, groundwater in the plain would be probably polluted by nitrate if irrational exploitation of land and water resources continued. Irrational human interferes and over-exploitation of land and water resources should be restricted so that groundwater quality and oasis environments can be protected and improved timely and sustainable development over the Sangong River basin can be ultimately realized.