基于证据权重法地下水中氮浓度影响因素分析

针对地下水中氮素浓度主控因素难以确定的问题,本文以三江平原松花江-挠力河流域为例,采用证据权重法,选取降水量、土地利用类型、人口密度、土壤有机质含量、粘土层厚度、地下水埋深、含水层厚度和地下水类型为证据因子,分别建立地下水中氨氮和硝态氮的预测模型,并分析其对氮素浓度分布的影响程度,取得了较好的预测结果,其中氨氮和硝态氮的预测精度分别达到77.2%和89.1%.分析表明:三江平原地下水中氨氮和硝态氮浓度与降水量、人口密度呈正响应关系;氨氮浓度与含水层厚度呈正响应关系,而硝态氮与含水层厚度则呈负响应关系,说明氨氮受含水层氧化还原环境条件影响较大,硝态氮受含水层对流弥散作用影响较大;当土地利用类型为居住用地时,地下水中氨氮和硝态氮浓度通常较高.

Influencing factors of nitrogen concentration in groundwater based on weights of evidence method

For the difficulty of identifying the primary factors controlling the nitrogen concentration in groundwater, this work firstly selected precipitation, land-use pattern, population density, soil organic matter content, thickness of clay layer, groundwater depth, aquifer thickness, and groundwater type as evidence factors and analyzed their influence on the distribution of the nitrogen concentration in groundwater, through a case study of the Songhua River-Naoli River Watershed in the Sanjiang Plain. Based on the Weights of Evidence (WofE) method, the separate prediction models for ammonia nitrogen and nitrate nitrogen were then established, which successfully predicted the concentrations of ammonia nitrogen and nitrate nitrogen in groundwater with the accuracy of 77.2% and 89.1%, respectively. The findings demonstrated the positive correlations among the nitrate nitrogen and ammonia nitrogen concentrations in groundwater and the precipitation as well as population density in the Sanjiang Plain. While the concentration of ammonia nitrogen responded positively to aquifer thickness, the concentration of nitrate nitrogen responded negatively, indicating that the redox environment of the aquifer had a significant impact on ammonia nitrogen while the nitrate nitrogen was more affected by the convection and dispersion in the aquifer. In addition, the concentrations of ammonia nitrogen and nitrate nitrogen in groundwater were found usually high in the studied residential area.