Relic surface water (clay-pore water) input triggers arsenic release into the shallow groundwater of Bengal aquifers
Relic surface water (clay-pore water) input triggers arsenic release into the shallow groundwater of Bengal aquifers
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DOI：
10.1007/s12040-022-01819-y
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发表时间：
2022-06-01
影响因子：
1.9
通讯作者：
Meeran, Kathiravan
中科院分区：
文献类型：
--
作者：
Pathak, Pousali;Ghosh, Prosenjit;Meeran, Kathiravan
地下水中砷的地质来源是不争的事实。西孟加拉邦浅层地下水中的砷污染是一个令人担忧的健康问题，因为该地区人口和对水的需求不断增长。浅层地下水中的砷污染是由微生物活动促进的，微生物活动依赖于溶解有机碳(DOC)的流入，为从含水层沉积物中释放砷提供了一个临时的还原条件。在这里，我们提供了几年来对浅层地下水、“深池塘水”(从沉积物-水界面上方的池塘最深处收集)、河水和雨水中溶解的总砷含量和稳定同位素比率进行了多年的季节性观测的文件，这些水来自西孟加拉邦哈林哈塔区块的Chakdaha地区。目前的研究首次表明，季节性深池塘水的同位素组成与浅含水层夹层粘土沉积物捕获的孔隙水的同位素组成有很大的相似之处(数据取自孟加拉国地区的文献)。我们重点介绍了干旱时期季节性富营养化、季风期洪水和沉积允许富含有机的粘土沉积物与富含DOC的孔隙水埋藏的可能过程，这些孔隙水是粘土口袋孔隙水的来源。在历史时间尺度上形成的粘土-孔隙水的同位素组成与地表水体的深底水组成相似，为触发As季节性释放到浅层地下水提供了理想的组成。干旱时期地下水的过量抽取和含水层沉积物夹层粘土透镜的挤压等过程，可以将其富含的有机物质排出，引发厌氧微生物活动，并将As释放到邻近的水中。用D-过量和增量O-18作为保守示踪剂，我们已经证明了类似于13-14%的粘土-孔隙水混合(排除)到毗邻的As-未受污染的(10微克/L)动员。
The geogenic source of arsenic (As) in groundwater is an indisputable fact. Arsenic contamination in the shallow groundwater of West Bengal is an alarming health issue with progressive growth of regional population and demand for water. The As contamination in shallow groundwater is facilitated by microbial activities, which depend on the inflow of dissolved organic carbon (DOC), providing a temporary reducing condition conducive to the release of As from aquifer sediments. Here, we present a documentation over several years of seasonal observations on dissolved total As contents and stable isotope ratios in shallow groundwater, 'deep pond water' (collected from the deepest part of the pond just above the sediment-water interface), river water and rainwater from the Chakdaha region, Haringhata block, Nadia district, West Bengal. The current study shows, for the first time, a large similarity in the isotopic composition of seasonal deep pond water with the shallow aquifer-intercalated clay sediment-trapped pore water (data adopted from the literature on a Bangladesh region). We highlight the possible processes wherein seasonal eutrophication during dry time followed by monsoon time flooding and sedimentation allows the burial of organic-rich clayey sediments with trapped DOC-rich pore water, which serve as a source of clay-pocket pore water. The isotopic composition of clay-pore water formed at a historical time scale resembles the deep-bottom water composition of surface water bodies and provides an ideal composition responsible for triggering the seasonal release of As into the shallow groundwater. The processes such as excess withdrawal of groundwater during dry periods and consequent squeezing of aquifer sediment-intercalated clay-lenses can expel its organic-rich contents to trigger anaerobic microbial activities and As release into the adjoining water. Using D-excess and delta O-18 as conservative tracers, we have shown that similar to 13-14% mixing (exclusion) of clay-pore water to the adjoining As-uncontaminated (10 mu g/L) mobilisation.