Department of Civil and Traffic Engineering, Yellow River Conservancy Technical Institute, Kaifeng, Henan, China.
Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences, Shijiazhuang, China.
Water Environ Res. 2024 Jul;96(7):e11076. doi: 10.1002/wer.11076.
Knowledge on natural background levels (NBLs) of aluminum (Al) in groundwater can accurately assess groundwater Al contamination at a regional scale. However, it has received little attention. This study used a combination of preselection and statistic methods consisting of the oxidation capacity and the boxplot iteration methods to evaluate the NBL of shallow groundwater Al in four groundwater units of the Pearl River Delta (PRD) via eliminating anthropogenic-impacted groundwaters and to discuss driving factors controlling high NBLs of Al in groundwater in this area. A total of 280 water samples were collected, and 18 physico-chemical parameters including Redox potential, dissolved oxygen, pH, total dissolved solids, HCO , NH , NO , SO , Cl, NO , F, K, Na, Ca, Mg, Fe, Mn, and Al were analyzed. Results showed that groundwater Al NBLs in groundwater units A-D were 0.11, 0.16, 0.15, and 0.08 mg/L, respectively. The used method in this study is acceptable for the assessment of groundwater Al NBLs in the PRD, because groundwater Al concentrations in various groundwater units in residual datasets were independent of land-use types, but they were opposite in the original datasets. The dissolution of Al-rich minerals in sediments/rocks was the major source for groundwater Al NBLs in the PRD, and the interaction with Al-rich river water was secondary one. The high groundwater Al NBL in groundwater unit B was mainly attributed to the acid precipitation and the organic matter mineralization inducing the release of Al in Quaternary sediments. By contrast, the high groundwater Al NBL in groundwater unit C mainly was ascribed to the release of Al complexes such as fluoroaluminate from rocks/soils into groundwater induced by acid precipitation, but it was limited by the dissolution of Mg minerals (e.g., dolomite) in aquifers. This study provides not only useful groundwater Al NBLs for the evaluation of groundwater Al contamination but also a reference for understanding the natural geochemical factors controlling groundwater Al in urbanized deltas such as the PRD. PRACTITIONER POINTS: The natural background level (NBL) of groundwater aluminum in the Pearl River Delta (PRD) was evaluated. The dissolution of aluminum-rich minerals in sediments/rocks was the major source for groundwater aluminum NBLs in the PRD. The acid precipitation and organic matter mineralization contribute to high groundwater Al NBL in the groundwater unit B. The acid precipitation contributes to high groundwater Al NBL in the groundwater unit C, while dissolution of magnesium minerals limits it.
地下水铝的自然背景水平（NBL）知识可以准确评估区域范围内地下水铝的污染程度。然而，这一问题还没有引起足够的重视。本研究采用预筛选和统计方法相结合的方式，利用氧化能力和箱线迭代方法，排除人为影响的地下水，评估了珠江三角洲（PRD）四个地下水单元浅层地下水中铝的 NBL，并讨论了该地区控制地下水高铝 NBL 的驱动因素。共采集了 280 个水样，分析了包括氧化还原电位、溶解氧、pH 值、总溶解固体、HCO 、NH 、NO 、SO 、Cl 、NO 、F、K、Na、Ca、Mg、Fe、Mn 和 Al 在内的 18 种理化参数。结果表明，地下水单元 A-D 的地下水铝 NBL 分别为 0.11、0.16、0.15 和 0.08mg/L。本研究中使用的方法适用于评估 PRD 地区的地下水铝 NBL，因为在残差数据集中，各个地下水单元的地下水铝浓度与土地利用类型无关，但在原始数据集中则相反。沉积物/岩石中富铝矿物的溶解是 PRD 地区地下水铝 NBL 的主要来源，而与富铝河水的相互作用则是次要来源。地下水单元 B 中高浓度的地下水铝 NBL 主要归因于酸性降水和有机质矿化作用导致第四纪沉积物中铝的释放。相比之下，地下水单元 C 中高浓度的地下水铝 NBL 主要归因于酸性降水诱导岩石/土壤中的氟铝酸盐等铝配合物释放到地下水中，但受含水层中白云石等镁矿物溶解的限制。本研究不仅为评估地下水铝污染提供了有用的地下水铝 NBL，也为理解城市化三角洲（如 PRD）中控制地下水铝的自然地球化学因素提供了参考。
评估了珠江三角洲（PRD）地下水铝的自然背景水平（NBL）。
沉积物/岩石中富铝矿物的溶解是 PRD 地区地下水铝 NBL 的主要来源。
酸性降水和有机质矿化作用导致地下水单元 B 中高浓度的地下水铝 NBL。
酸性降水导致地下水单元 C 中高浓度的地下水铝 NBL，但镁矿物的溶解限制了其浓度。
