Environmental tracers to evaluate groundwater residence times and water quality risk in shallow unconfined aquifers in sub Saharan Africa
Environmental tracers to evaluate groundwater residence times and water quality risk in shallow unconfined aquifers in sub Saharan Africa
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用于评估撒哈拉以南非洲浅层无承压含水层地下水停留时间和水质风险的环境示踪剂
DOI：
10.1016/j.jhydrol.2020.125753
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发表时间：
2021
影响因子：
6.4
通讯作者：
Banks E
中科院分区：
文献类型：
--
作者：
Banks E
在撒哈拉以南非洲，浅层含水层系统是农村社区主要的安全和有保障的水资源。随着地下水开发的增加，关于地下水抽取的可持续性和脆弱性的信息变得越来越重要。作为UpGro联合会项目-隐藏的危机的一部分，对150个深度在15米至101米之间的手泵钻孔进行了调查，以检查埃塞俄比亚高地含水层系统的恢复能力，以及乌干达和马拉维的结晶基底岩石。环境示踪剂（氯氟烃（CFCs）、SF6、氯化物和水的稳定同位素）、水质指标（硝酸盐和大肠杆菌）。大肠杆菌）和地下水位时间序列数据被用来估计区域范围（100- 10 000平方公里）的地下水停留时间和补给，并调查不同时间范围内水质和供水所面临的风险以及地质和气候环境。使用三种不同的技术（氟氯化碳、氯化物质量平衡、地下水位波动法）估算的埃塞俄比亚、乌干达和马拉维的平均补给率分别为30 - 330、27-110和30-170毫米年。这些补给估计表明，从分散的低产HPB中提取是可持续的。降雨和地下水中稳定同位素的比较表明，在补给之前几乎没有蒸发，补给事件偏向于降雨量较大和降雨事件较强的月份。在埃塞俄比亚或马拉维的大肠杆菌和氯氟烃。E.在大部分地点（埃塞俄比亚= 38%，乌干达= 65%和马拉维= 47%）发现的大肠杆菌表明，受污染的地表水迅速进入钻孔，地下水中CFC-12浓度低于75 pg kg− 1的大肠杆菌表明，非常年轻的水与超过40年的水混合。快速交通通道最有可能与损坏的HPB渠首工程和不良施工有关。在几个受监测的HPB中，由于抽水导致的每日水位下降使地下水位接近HPB的底部，这表明这些HPB位于渗透性低的含水层部分，或者设计不良，为增加的需求提供有限的容量。需要改善HPB的选址和建设，以及地下水位监测，以利用浅层含水层中更具弹性的地下水，并为农村社区提供充足和优质的供水。
In sub-Saharan Africa, shallow aquifer systems are relied on as the main safe and secure water resource available to rural communities. Information on the sustainability and vulnerability of groundwater abstraction is becoming increasingly important as groundwater development increases. As part of the UpGro Consortium Project- Hidden Crisis, 150 hand pumped boreholes (HPBs), ranging between 15 and 101 m depth were investigated to examine the resilience of aquifer systems in the Ethiopian Highlands, and the crystalline basement rocks of Uganda and Malawi. Environmental tracers (chlorofluorocarbons (CFCs), SF6, chloride and the stable isotopes of water), water quality indicators (nitrate and E. coli), and groundwater-level time series data were used to estimate groundwater residence time and recharge at a regional scale (100–10,000 km2) and investigate the risks to water quality and water supply over different timeframes, and geological and climatic environments. Average estimated recharge rates using three different techniques (CFCs, chloride mass balance, water table fluctuation method) were between 30 and 330, 27–110 and 30–170 mm y−1, for sites in Ethiopia, Uganda and Malawi, respectively. These estimates of recharge suggests abstraction from dispersed low-yielding HPBs is sustainable. Comparison of stable isotopes in rainfall and groundwater indicates that there is little evaporation prior to recharge, and recharge events are biased to months with greater rainfall and more intense rainfall events There was a weak correlation between nitrate and CFCs within all three countries, and no correlation between E. coli and CFCs within Ethiopia or Malawi. The presence of E. coli at a large proportion of the sites (Ethiopia = 38%, Uganda = 65% and Malawi = 47%) suggests rapid transit of contaminated surface water into the borehole and its presence in groundwater that has CFC-12 concentrations less than 75 pg kg−1indicates mixing of very young water with water >40 years old. The rapid transit pathways are most likely associated with damaged HPB headworks and poor construction. In several monitored HPBs, daily drawdown due to pumping, drew the groundwater levels close to the base of the HPB, indicating that these HPBs were located in parts of the aquifer with low permeability, or were poorly designed, offering limited capacity for increased demand. Improved HPB siting and construction, coupled with groundwater level monitoring are required to capitalise on the more resilient groundwater within the shallow aquifers and safeguard adequate and good quality water supply for rural communities.
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DOI：
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DOI：
--
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