鄂尔多斯盆地多级次地下水流系统中硝酸盐分布特征及其成因

水资源短缺的鄂尔多斯盆地内地下水遭受硝酸盐(NO₃^-)污染等问题日益突出,识别盆地不同地下水流系统的NO₃^-分布规律及其成因,对地下水资源的合理利用与保护具有重要意义。选取鄂尔多斯盆地北部湖泊集中区白垩系地下水系统为研究对象,基于水化学和聚类-主成分分析划分地下水流系统级次,在此基础上对比分析不同级次地下水流系统中NO₃^-分布特征,综合水化学和环境同位素分析识别多级次地下水流系统中NO₃^-来源及其潜在过程。研究表明:研究区ρ(NO₃^-)超出地下水质量标准(GB/T 14848-2017)Ⅲ类水标准的地下水样品集中在局部-中间地下水流系统,其超标率达到28%;区域地下水流系统中ρ(NO₃^-)均值约为1 mg/L。研究区不同级次地下水流系统中ρ(NO₃^-)分布特征主要与人类活动影响程度有关,而地下水蒸发富集和反硝化衰减作用对ρ(NO₃^-)的影响可以忽略。其中,局部-中间地下水流系统受到人类活动产生的污染影响显著,其NO₃^-污染主要来源于无机铵肥和粪便污水等;区域地下水流系统可能尚未受到人类活动污染,其NO₃^-来源于天然有机氮矿化。

Distribution characteristics and genesis of nitrate in nested groundwater flow system in northern Ordos Basin

Under the situation of water shortage and increasingly serious groundwater nitrate pollution in Ordos Basin, it is helpful for rational utilization and protection of groundwater resources to identify the distribution and causes of nitrate in different groundwater flow systems in Ordos Basin, so this research was carried out in the typical groundwater-fed lakes area within the basin.Hydrochemistry and multivariate statistical analysis (i.e., hierarchical cluster analysis and principal component analysis) were combined to identify the nested groundwater flow systems.Based on this, the distribution characteristics of nitrate in different groundwater flow systems were compared and analyzed.And both hydrochemistry and environmental isotopes were considered to further identify the sources and potential evolution processes of nitrate in nested groundwater flow systems.The results show that the groundwater samples with nitrate content exceeding the groundwater quality standard (GB/T 14848-2017) were taken from the local and intermediate groundwater flow system, with an over-standard rate reached 28%, and the mean nitrate content in the regional groundwater flow system is about 1 mg/L.The distribution of nitrate in different groundwater flow systems was dominated by the extent of human activities, while the influence of evaporation enrichment and denitrification attenuation processes can be ignored.And within the nested groundwater flow systems, the local and intermediate ones were significantly affected by pollution from human activities, with inorganic ammonium fertilizer and manure and sewage the main pollution sources of nitrate, but the regional one has not been polluted, with mineralization of natural organic nitrogen as its nitrate source.