US-Thailand Planning visits: Influence of climate on groundwater interactions with Mekong River: Implications for arsenic concentrations in alluvial aquifers

在整个南亚和东南亚，排出喜马拉雅山脉的河流沿线的含水层被大量用于旱季灌溉和家庭供水。以前的工作记录了这些河流三角洲含水层中砷(As)浓度升高的情况，这些河流包括恒河-雅鲁藏布江、红河和湄公河。在三角洲含水层的冲积含水层中进行的研究很少，但这些研究很少记录当地As浓度升高的情况。该地区的季风气候迫使河流和邻近含水层之间的水力梯度发生变化。由于水流大小和方向以及氧化还原条件的变化，这些梯度变化有可能影响地下水中痕量元素的行为。该项目与泰国坤健大学的研究人员开展了一项国际合作，从泰国东北部湄公河沿岸的一个冲积含水层收集初步的水文和地球化学数据。水井和河流将在旱季(11月)和季风季(5月至6月)进行采样，并对样品进行现场参数、主要离子、选定的微量元素、溶解有机碳和稳定同位素的分析。将在选定的井中安装设备，进行持续监测。这些数据将使追踪冲积含水层和湄公河之间的水流成为可能。该小组将开发冲积含水层-河流相互作用的概念模型，这将成为NSF水文科学计划建议的基础，以进行更长期和更密集的研究。研究结果将与泰国当地居民、教育工作者和政府机构分享，并通过泰国水利部S水文信息系统(HIS)与研究人员分享，并将在湄公河上拟议的大坝建设项目之前为含水层提供基线。该概念模型将为该地区的其他冲积含水层提供一个模板，例如缅甸的伊洛瓦底河谷，那里正在建造或计划修建大坝。非技术摘要：南亚和东南亚地区地下水中砷含量升高是一个严重的公共卫生问题。砷和其他微量元素在地下水中的行为与水文和地球化学过程有关，而这些过程又受到气候的影响。另一个可能的压力是大坝的建设，这极大地改变了河流和邻近含水层之间的联系。我们的目标是收集泰国东北部湄公河附近含水层在两个水文季节：旱季(11月)和季风季(5月至6月)期间地下水地球化学的初步数据集。这些结果将被用来开发一个概念模型，说明气候如何影响含水层与河流的相互作用，以及这些相互作用是否会影响含水层的浓度。这些数据将提供一个基线？在湄公河下游拟建大坝之前，对含水层的水质进行了评估。

Across South and Southeast Asia, aquifers along rivers draining the Himalayas are heavily utilized for dry-season irrigation and domestic water supply. Previous work has documented elevated arsenic (As) concentrations in the deltaic aquifers of these rivers, including the Ganges-Brahmaputra, the Red, and the Mekong. Few studies have been conducted in the alluvial aquifers upgradient of the deltaic aquifers, but those few have documented locally elevated As concentrations. The monsoonal climate of the region imposes shifts in hydraulic gradients between the river and adjacent aquifers. These gradient shifts have the potential to influence the behavior of trace elements in groundwater due to changes in flow magnitude and direction, as well as in redox conditions. This project initiates an international collaboration with investigators at Khon Kaen University, Thailand to collect preliminary hydrologic and geochemical data from an alluvial aquifer along the Mekong River in northeast Thailand. Wells and the river will be sampled during the dry season (November) and the monsoon season (May-June) and samples analyzed for field parameters, major ions, selected trace elements, dissolved organic carbon and stable isotopes. Equipment will be installed in selected wells for continuous monitoring. This data will enable tracking of flow between the alluvial aquifer and the Mekong. The group will develop a conceptual model of alluvial aquifer-river interactions, which will form the basis of a proposal to the NSF Hydrologic Sciences program for a longer-term and more spatially intensive study. Results will be shared with local residents, educators and government agencies in Thailand, and with researchers through CUAHSI?s Hydrologic Information Systems (HIS), and will provide a baseline for the aquifer prior to dam construction projects proposed on the Mekong. The conceptual model will offer a template for other alluvial aquifers in the region, such as the Irrawaddy valley of Myanmar, where dams are being built or planned. Non-technical abstract:Elevated arsenic (As) in groundwater across South and Southeast Asia is a critical public health problem. The behavior of As and other trace elements in groundwater is tied to hydrologic and geochemical processes, which are in turn influenced by climate. Another possible forcing is the construction of dams, which dramatically changes the connections between the river and the adjacent aquifers. Our goal is to collect a preliminary dataset on the geochemistry of groundwater in an aquifer adjacent to the Mekong River in northeast Thailand during two hydrologic seasons: the dry season (November) and the monsoon season (May-June). The results will be used to develop a conceptual model of how climate influences aquifer-river interactions, and if those interactions affect As concentrations in the aquifer. These data will provide a ?baseline? of water quality in the aquifer prior to construction of proposed dams on the Lower Mekong.