Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur, India.
Department of Environmental Science, SRM University-AP, Mangalagiri, Andhra Pradesh, India.
Environ Pollut. 2023 Feb 1;318:120838. doi: 10.1016/j.envpol.2022.120838. Epub 2022 Dec 7.
The role of submarine groundwater discharge (SGD) in transporting terrestrial-sourced arsenic (As) to the global oceans is not well documented. In the present study, executed on a coast adjoining the extensive groundwater As-contaminated Ganges river delta, we hypothesize that As-enriched groundwater discharges to the adjoining Bay of Bengal (BoB) through SGD flow paths. We conducted high-resolution, field-based investigations and thermodynamic modeling to understand the SGD-sourced As discharge and geochemical cycling of As and other redox-sensitive solutes along the discharge path under varying redox conditions and water sediment interactions. The As distribution and other solutes were measured in a series of multi-depth observation wells and sediment cores, extending from the high tide line (HTL) to 100 m toward the sea, for pre- and post-monsoon seasons. Results reveal the presence of a plume carrying up to 30 μg/L dissolved load of As toward the sea. Arsenic is associated with a plume of Fe and exhibits similar shore-perpendicular variability. Arsenic distribution and transport is controlled by the Fe-Mn redox cycle and influenced by terrestrial groundwater discharge. Field-observations and geochemical modeling demonstrate that Fe-hydroxide precipitates in the subterranean estuary and acts as an interim sink for As , which is eventually mobilized on alteration of geochemical conditions with the season. Fluctuating plume size can be attributed to seasonal variation in fresh groundwater input to the site. Estimates indicate up to 55mg/m/d As is released to BoB from the site. Based on physicochemical observations this study demonstrates the yet to be studied SGD derived As cycles and the role of SGD dynamics in controlling the fate of redox-sensitive contaminants and their discharge into global oceans.
海底地下水排泄（SGD）在将陆源砷（As）输送到全球海洋中的作用尚未得到充分记录。在本研究中，我们在毗邻广泛地下水砷污染恒河三角洲的海岸上进行了研究，假设富砷地下水通过 SGD 流径排泄到毗邻的孟加拉湾（BoB）。我们进行了高分辨率的现场调查和热力学模拟，以了解在不同氧化还原条件和水-沉积物相互作用下，沿排放路径的 SGD 来源的 As 排放和 As 及其他氧化还原敏感溶质的地球化学循环。在季风前和季风季节，我们在一系列多深度观测井和沉积物岩芯中测量了从高潮线（HTL）到朝向海洋 100 米的范围内的 As 及其他溶质的分布。结果表明，存在一个携带高达 30μg/L 溶解负荷的 As 向海的羽流。砷与铁羽流有关，并表现出类似的垂直岸线变化。砷的分布和运移受铁-锰氧化还原循环控制，并受陆地地下水排泄影响。现场观测和地球化学模拟表明，铁氢氧化物在地下河口沉淀，并作为 As 的临时汇，最终随着季节的变化，在地球化学条件改变时被释放出来。羽流大小的波动可能归因于现场新鲜地下水输入的季节性变化。估计表明，该地点每年向 BoB 释放高达 55mg/m/d 的 As。基于物理化学观测，本研究证明了尚未研究的 SGD 衍生的 As 循环以及 SGD 动力学在控制氧化还原敏感污染物的命运及其向全球海洋排放中的作用。
