快速城镇化三角洲地区高碘地下水赋存特征及驱动因素:以珠江三角洲为例

Geochemical Characteristics and Driving Factors of High-Iodine Groundwater in Rapidly Urbanized Delta Areas: A Case Study of the Pearl River Delta

沿海城镇化地区地下水中碘来源复杂,高碘地下水对生活饮用水安全存在潜在威胁.以城镇化快速发展的珠江三角洲为研究区,运用数理统计和主成分分析等方法探讨了珠江三角洲不同含水层和不同城镇化水平地区浅层地下水中碘的赋存特征及驱动因素.结果表明,研究区浅层地下水ρ(I^(-))介于未检出~2.34 mg·L^(-1),主要以I^(-)的形式存在.研究区1 567组地下水样品中,ρ(I^(-))>0.1 mg·L^(-1)的高碘地下水检出120组.其中,孔隙和裂隙高碘地下水分别检出84组和36组,岩溶含水层未检出高碘地下水.对比2005~2008年历史水化学数据,近10年新增建设用地浅层地下水ρ(I^(-))均值增加了30%.孔隙和裂隙高碘地下水均主要分布在城镇化地区,其比例均为非城市化地区的3倍以上.高碘地下水以HCO_(3)·Cl-Ca·Na和Cl-Na型水为主,高碘地下水具有pH较高氧化还原电位较低等特性.含碘铁锰(氧)氢氧化物的还原溶解和沉积物中富碘有机物的分解可能是珠江三角洲平原区浅层孔隙高碘地下水的主要来源.富含碳酸盐的岩石中有机物的降解和城市化伴随还原性污水的泄漏,可能为浅层裂隙高碘地下水的主要来源.三角洲平原区中性至弱碱性富含有机质的还原环境是高碘地下水赋存的主要成因.风化溶滤、阳离子交换和海陆交互作用是珠江三角洲高碘地下水演变的主要水化学过程.

The source of iodine in the groundwater of coastal urbanization areas is complex, and high-iodine groundwater is a potential threat to the safety of drinking water. Based on this, this study took the Pearl River Delta, which is developing rapidly in urbanization, as the research area. Additionally, the occurrence characteristics and driving factors of iodide in shallow groundwater of different aquifers and different urbanization levels in the Pearl River Delta were studied using mathematical statistics, principal component analysis, and other methods. The results showed that the concentration of iodide in the shallow groundwater was 2.34 mg·L^(-1)and undetected in the form of I^(-). Among 1 567 groundwater samples in the study area, there were 120 groups of groundwater with high iodine content greater than 0.1 mg·L^(-1), accounting for 7.7%. Among them, 84 and 36 groups were detected in shallow porous and shallow fissure high-iodine groundwater, respectively, whereas no high-iodine groundwater was detected in the karst aquifer. The proportion of high-iodine groundwater was 8.0% in the shallow porous aquifer and 7.5% in the shallow fissure aquifer. Both the porous aquifer and the fissured aquifer with high iodine content were mainly distributed in the urbanized areas, the proportion of which was more than three times that of the non-urbanized areas. The chemical types of the high-iodine groundwater were mainly HCO_(3)·Cl-Ca·Na and Cl-Na type water, which have the characteristics of high pH and low redox potential. The reduction and dissolution of iodine-containing Fe/Mn(oxygen) hydroxides and the decomposition of iodine-rich organics in sediments may be the main sources of high-iodine groundwater in the shallow porous aquifers of the Pearl River Delta Plain. The degradation and urbanization of organic matter in carbonate-rich rocks is accompanied by the leakage of reducing sewage, which may be the main source of high-iodine groundwater in shallow fissured aquifers. The neutral to weakly alkaline reduction environment with rich organic matter was the main cause of high-iodine groundwater in the Delta Plain area. Weathering, leaching, cation exchange, and sea-land interactions are the main hydrogeochemical processes in the evolution of high-iodine groundwater in the Pearl River Delta.