浅层地下水埋深、矿化度及硝酸盐污染的空间分布特征

Spatial distribution of shallow groundwater depth,total dissolved solid and nitrate pollution

对银川平原101个观测井取样分析,测定了其浅层地下水位埋深、矿化度及硝酸盐含量。应用地统计学方法结合GIS技术对数据进行了分析。结果表明,地下水埋深服从正态分布,而矿化度和硝酸盐服从对数正态分布。银川平原地下水位埋深、矿化度和硝酸盐含量的平均值分别为1.78m,1.81g/L和3.17mg/L。三者在一定范围内均存在空间相关性,它们的空间相关距离分别为23.7、13.3和12.6km。运用Kriging方法对未测点进行了估值,绘制了三者的空间分布图。银川平原地下水埋深总体较浅,研究区约有75.1%的地区地下水埋深为1.5～2.0m,发现在平原中部的银川地区一带形成了以新旧城区为中心的地下水位降落漏斗区。地下水矿化度在整个平原内自西南向东北呈逐渐升高的趋势,其中66.4%的区域达到了农田灌溉水质标准。仅有3.7%的局部地区的地下水硝酸盐含量超过了饮用水水质标准。

A total 101 water samples were collected from observing wells in Yinchuan Plain.The groundwater depth, total dissolved solid(TDS)and nitrate content of groundwater were measured.The geostatistical method and GIS technique were used to analyze the data.The results indicated that the groundwater depth showed a normal distribution, while TDS and nitrate content were lognormally distributed.The average groundwater depth,TDS and nitrate concentration were 1.78m,1.81g/L and 3.17mg/L in Yinchuan plain in 2005,respectively.The semivariance analysis indicated that those observed items were spatial correlated in a given spatial range,and their spatial correlated distances were 21.6,13.3 and 12.6km,respectively.The Kriging method was applied to estimate the unobserved points and generated their spatial distribution map.It was found that the shallow groundwater depth in Yinchuan plain was fairly small,and the groundwater depth range from 1.5 to 2.0m was about 75.1%of the whole area,but there existed a funnel region of groundwater table around both new and old urban districts of Yinchuan city located in the middle of the plain, and over-extraction of groundwater was the main reason for that.TDS showed an obvious increasing trend from southwest to northeast across the plain,of which 66.4%reached the standard for irrigation water quality(2 g/L).The low shallow groundwater table,strong evaporation,together with poor runoff and exchange capacity of groundwater resulted in high TDS.Only 3.7%of total area which nitrate content exceeded the limit of 10 mg/L for drinking water.The infiltration of industrial sewage and excessive nitrogen fertilizer application were responsible for that.