Geochemical and hydrogeological contrasts between shallow and deeper aquifers in two villages of Araihazar, Bangladesh: Implications for deeper aquifers as drinking water sources
Geochemical and hydrogeological contrasts between shallow and deeper aquifers in two villages of Araihazar, Bangladesh: Implications for deeper aquifers as drinking water sources
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DOI：
10.1016/j.gca.2005.06.001
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发表时间：
2005-11
影响因子：
5
通讯作者：
Y. Zheng;A. Geen;M. Stute;R. Dhar;Z. Mo;Zhongqi Cheng;A. Horneman;I. Gavrieli;H. Simpson
中科院分区：
文献类型：
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作者：
Y. Zheng;A. Geen;M. Stute;R. Dhar;Z. Mo;Zhongqi Cheng;A. Horneman;I. Gavrieli;H. Simpson
对孟加拉国两个村庄的沉积物和地下水剖面进行了比较，以了解调节地下水中溶解砷浓度的地球化学和水文地质因素。在这两个村庄，细粒沉积层将砷含量< 28 m的浅层含水层与砷含量< 10 μg/L的深层含水层（40-90 m）分开。在一个村庄（达里），放射性碳定年法表明，深层含水层沉积物沉积于大约50万年前，地下水年龄为数千年。在另一个村庄（海湾），沉积物年龄小于20 ka，直至90 m，较深的含水层地下水较年轻，约为数百年。两个村庄的浅层含水层砷含量都很高，含有炸弹- 3h和炸弹- 14c，表明最近有补给。浅层和深层含水层的主、次离子组成也存在显著差异。深层水为Na+- hco3型，溶解NH4+（76±192 μmol/L）、Fe（27±43 μmol/L）和Mn（3±2 μmol/L）相对较少。浅层水为Ca2+-Mg2+- hco3型，溶解NH4+（306±355 μmol/L）、Fe（191±73 μmol/L）、Mn（27±43 μmol/L）浓度升高。在这两个村庄，用1 mol/L磷酸盐溶液从深层含水层砂中可提取的砷（0.2±0.3 mg/kg, n = 12; 0.1±0.1 mg/kg, n = 5）比从浅层沉积物中可提取的砷（1.7±1.2 mg/kg, n = 9; 1.4±2.0 mg/kg, n = 11）低一个数量级。这些差异表明沉积物中磷可提取砷的浓度是控制地下水中砷浓度的一个因素。在两个低砷的深层含水层中都观察到低磷可提取砷水平，尽管在两个村庄这些含水层的沉积时间有很大差异。本研究中提供的地球化学数据和水文曲线表明，只要取水量不超过1厘米/年的补给速率，砷含量低的全新世和更新世深层含水层都应该是可行的饮用水来源。
Sediment and groundwater profiles were compared in two villages of Bangladesh to understand the geochemical and hydrogeological factors that regulate dissolved As concentrations in groundwater. In both villages, fine-grained sediment layers separate shallow aquifers (< 28 m) high in As from deeper aquifers (40–90 m) containing < 10 μg/L As. In one village (Dari), radiocarbon dating indicates deposition of the deeper aquifer sediments > 50 ka ago and a groundwater age of thousands of years. In the other village (Bay), the sediment is < 20 ka old down to 90 m and the deeper aquifer groundwater is younger, on the order of hundreds of years. The shallow aquifers in both villages that are high in As contain bomb-3H and bomb-14C, indicating recent recharge. The major and minor ion compositions of the shallow and deeper aquifers also differ significantly. Deeper aquifer water is of the Na+-HCO3–type, with relatively little dissolved NH4+(76 ± 192 μmol/L), Fe (27 ± 43 μmol/L) and Mn (3 ± 2 μmol/L). In contrast, shallow aquifer water is of the Ca2+-Mg2+-HCO3–type, with elevated concentrations of dissolved NH4+(306 ± 355 μmol/L), Fe (191 ± 73 μmol/L), and Mn (27 ± 43 μmol/L). In both villages, the quantity of As extractable from deeper aquifer sands with a 1 mol/L phosphate solution (0.2 ± 0.3 mg/kg, n = 12; 0.1 ± 0.1 mg/kg, n = 5) is 1 order of magnitude lower than P-extractable As from shallow deposits (1.7 ± 1.2 mg/kg, n = 9; 1.4 ± 2.0 mg/kg, n = 11). The differences suggest that the concentration of P-extractable As in the sediment is a factor controlling the concentration of As in groundwater. Low P-extractable As levels are observed in both deeper aquifers that are low in As, even though there is a large difference in the time of deposition of these aquifers in the two villages. The geochemical data and hydrographs presented in this study suggest that both Holocene and Pleistocene deeper aquifers that are low in As should be a viable source of drinking water as long as withdrawals do not exceed recharge rates of ∼1 cm/yr.