基于GIS的华北高产粮区地下水硝态氮含量时空变异特征

集约化农业生产区地下水的硝酸盐污染是一个十分普遍的问题.选取华北平原典型高产粮区桓台县为研究对象,分别在2002年和2007年同一季节对该县境内的394个潜水水样和283个承压水水样的硝态氮含量进行了取样分析,应用地质统计学与GIS技术相结合的方法对其时空变异规律进行了分析.结果表明,2002年和2007年潜水硝态氮的平均含量分别为8.08 mg·L~(-1)和14.68 mg·L~(-1),承压水硝态氮的平均含量分别为3.87 mg·L~(-1)和7.19 mg·L~(-1),2007年比2002年含量增幅均接近1倍.2个时期承压水硝态氮含量的空间相关距离均远大于潜水硝态氮含量的相关距离.2007年与2002年相比,潜水硝态氮含量各等级(0～5、 5～10、 10～15、 15～20、 20～30和>30 mg·L~(-1))的面积变化幅度分别为-28.87%、 -14.63%、 13.06%、 14.37%、 12.23%和3.85%;承压水中前4个等级的面积变幅分别为-37.82%、 28.01%、 9.33%和0.48%.通过对地下水硝态氮含量的垂向分析发现,2个时期的承压水硝态氮含量与取样井深存在显著负相关关系,并且深层承压水的硝酸盐含量呈现上升趋势.

GIS-based Analysis of Spatio-temporal Variability of Groundwater Nitrate Concentration in High-yield Region in North China Plain

Nitrate pollution in groundwater is very widespread in intensive agricultural region. 394 samples from phreatic water wells and 283 samples from confined water wells were collected across Huantai County at the same season of 2002 and 2007, which is representative of high-yield region of North China Plain. The NO^-₃-N concentration was determined. Geostatistics combined with GIS technique were used to analyze the spatio-temporal variability of groundwater nitrate concentration. The average nitrate concentrations in phreatic water were 8.08 mg·L^-1 and 14.68 mg·L^-1 in 2002 and 2007 respectively, and that in confined water were 3.87 mg·L^-1 and 7.19 mg·L^-1 respectively. The spatial correlation distances of nitrate concentrations in confined water for both periods were greater than that in phreatic water. The mapping showed that the areas of phreatic groundwater with high levels of nitrate concentrations (10-15, 15-20, 20-30, and >30 mg·L^-1) increased by 13.06%, 14.37%, 12.23%, and 3.85% from 2002 to 2007, while the area with low levels (0-5 and 5-10 mg·L^-1) nitrate concentrations were decreased by 28.87% and 14.63% compared with 2002. However, the areas of confined water with nitrate concentrations of 5-10 mg·L^-1, 10-15 mg·L^-1and 15-20 mg·L^-1 were increased by 28.01%, 9.33%, and 0.48% respectively, while the areas of NO^-₃-N concentration (0-5 mg·L^-1) was decreased by 37.82%. The NO^-₃-N concentration in confined water was significantly negative related to groundwater depth for the two period, we found an increasing trend of NO^-₃-N concentration in the deeper confined water from 2002 to 2007.