快速城镇化进程中珠江三角洲高铵地下水赋存环境及驱动因素

Geochemical characteristics and driving factors of high-ammonium groundwater in the rapid urbanization of the Pearl River Delta

地下水中高浓度的铵态氮对生活饮用水安全及生态环境存在潜在威胁。相比较硝态氮,高浓度的铵态氮不仅有各种人为来源,天然沉积环境更是造成高铵地下水的主要成因。本文以城镇化快速发展的珠江三角洲为研究区,运用数理统计、主成分分析等方法深入探讨了研究区高铵地下水的赋存环境特征及驱动因素。结果表明,研究区地下水中NH_(4)^(+)质量浓度介于未检出~180 mg/L。研究区1539组地下水样品中,NH_(4)^(+)质量浓度大于10 mg/L的高铵地下水69组,其中含NH_(4)^(+)质量浓度大于30 mg/L的高铵“肥水”23组。对比2005—2008年历史水化学数据,2009—2018年新增建设用地孔隙含水层高铵地下水样品比例增加25%。高铵地下水呈斑块状分布于三角洲平原区第四系底部低洼的基底、洼地等退积层序发育的淤泥质含水层中。淤泥层等富含有机质和总有机碳的沉积层是珠江三角洲地区的“生铵层”,有机氮的矿化是三角洲平原区城市化孔隙含水层中高铵地下水的主要驱动力。城镇化扩张引起生活污水及富铵工业废水的泄漏入渗是城乡结合部高铵地下水铵氮的重要来源。三角洲平原区中性至弱碱性富含有机质的还原环境是高铵地下水的主要成因。风化溶滤、阳离子交换吸附、海陆交互作用是珠江三角洲高铵地下水质演变的主要水文地球化学过程。

High concentration of ammonium nitrogen in groundwater is a potential threat to drinking water safety and ecological environment.Compared with nitrate nitrogen,the high concentration of ammonium nitrogen not only has a variety of man-made sources,but also the natural sedimentary environment is the main cause of high ammonium groundwater.The rapid urbanization of the Pearl River Delta was taken as a case study to investigate the environmental characteristics and driving factors of high ammonium groundwater by means of mathematical statistics and principal component analysis methods.The results show that the concentration of ammonium in the groundwater in the study area is as high as-180 mg/L.Among 1539 groups of groundwater samples,69 groups of high-ammonium groundwater with ammonium ion concentration greater than 10 mg/L,23 groups of high-ammonium fertilizer water yield ammonium ion concentration greater than 30 mg/L.Compared with the historical hydrochemical data from 2005 to 2008,the proportion of high-ammonium groundwater sample sites in the pore aquifers of newly-added construction land from 2009 to 2018 is 6.5%,which is 1.25 times that of ten years ago.The high ammonium groundwater is distributed in the silty and silty aquifer developed in the low lying basement and depression at the bottom of Quaternary in the delta plain area.The sediments rich in organic matter and total organic carbon,such as silt layer,are the"ammonium producing layer"in the Pearl River Delta region,and the mineralization of organic nitrogen is the main driving force of the high ammonium groundwater in the urbanized pore aquifer in the delta plain region.The leakage and infiltration of domestic sewage from urbanization expansion and ammonium-rich industrial wastewater are the important sources of ammonium-nitrogen in high ammonium-rich groundwater in the urban-rural junction.The reduction environment rich in organic matter is the main cause of the high ammonium groundwater in the delta plain.Lixiviation,cation exchange adsorption and sea-land interaction are the main hydrogeochemical processes of the evolution of high-ammonium groundwater water quality in the Pearl River Delta.