Geochemical Transformations in Subterranean Estuaries: Reactions, Rates, and Fluxes to the Coastal Ocean

在这个项目中，伍兹霍尔海洋研究所的研究人员将研究几种关键元素在通过沿海含水层的地下河口时的地球化学变化和通量。 最近的研究表明，海底地下水排放（SGD）可能有助于溶解的化学物种到海洋的显着通量。然而，这种通量的大小是强烈影响的地下河口，定义为地下水和海水在沿海含水层之间的混合区发生的地球化学过程。越来越多的证据表明，地下河口在地球化学循环中起着重要的作用，因此，我们必须了解这些过程，以便确定SGD在海洋元素预算中的作用。为了做出这一决定，我们必须首先了解地下河口尺度上对这些元素起作用的主要地球化学反应。本研究的主要目的是确定控制具有对比地球化学行为的几种元素循环的过程：（1）氧化还原敏感元素Fe、Mn和U，以及（2）Sr、Ba和Ra，它们对氧化还原条件和（例如吸附锰氧化物）以及盐通过地下河口的运输所驱动的离子强度的变化。该项目由地球化学家和水文地质学家之间的独特合作努力组成，他们将通过实地研究、受控实验室实验和水文地质流动模型的结合来实现项目目标。 更具体地说，拟议的项目将通过季节性地下水取样和地表水调查，更深入地探讨地下河口的氧化还原和盐度驱动的生物地球化学反应。 为了支持实地工作，研究小组将在现场开发一个密度相关流动的模拟模型。 最后，一系列的实验室柱实验将进行以下释放和/或去除的Sr，Ba，Ra，和U从含水层沉积物在不同的温度，盐度和氧化还原条件下。 更广泛的影响：地下河口与地表河口类似，具有发生重大地球化学变化的潜力，阐明这些机制可能对理解其他地区沿海地下水地球化学具有重要影响。虽然SGD对某些元素的全球循环的整体重要性目前尚不确定，但毫无疑问，SGD在美国和世界各地的地方规模上都很重要。 富含营养物（磷酸盐、硝酸盐、铵）的地下水进入沿海沃茨和海湾并不罕见，是SGD的一个重要环境组成部分。 因此，更好地了解地下河口的地球化学制度具有重要的水质影响沿海含水层，并允许洞察基本的生物地球化学反应在一个主要的淡水/海水界面。 这个项目有一个重要的教育组成部分，并寻求资助研究生和本科生谁一直在这个项目上工作，因为高中推广计划（讲座，海报）与瓦奎特湾国家河口研究保护区。

ABSTRACTOCE-0425061In this project, researchers at the Woods Hole Oceanographic Institution will study e the geochemical transformations and fluxes of several key elements as they pass through the subterranean estuary of a coastal aquifer. Recent studies indicate that submarine groundwater discharge (SGD) may contribute significant fluxes of dissolved chemical species to the oceans. However, the magnitude of such fluxes is strongly influenced by biogeochemical processes occurring in the subterranean estuary, defined as the mixing zone between groundwater and seawater in a coastal aquifer. Evidence is mounting that the subterranean estuary plays an important role in geochemical cycling and it is therefore critical that we understand these processes so that the role of SGD in oceanic elemental budgets can be determined. In order to make this determination, we must first understand the major geochemical reactions operating on such elements on the scale of subterranean estuaries. The main objective of this study is to identify the processes that control the cycling of several elements having contrasting geochemical behavior: (1) the redox sensitive elements Fe, Mn, and U, and (2) Sr, Ba, and Ra, which are sensitive to both redox conditions (e.g. sorption to Mn oxides) and changes in ionic strength driven by salt transport through the subterranean estuary.The project consists of a unique collaborative effort between a geochemist and a hydrogeologist, who will achieve project objectives through a combination of field studies, controlled laboratory experiments, and hydrogeologic flow modeling. More specifically, the proposed project will probe deeper into redox and salinity-driven biogeochemical reactions in a subterranean estuary through seasonal groundwater sampling coupled with surface water surveys. In support of the field work, the research team will develop a simulation model of density-dependent flow at the site. Finally, a series of laboratory column experiments will be conducted to follow the release and/or removal of Sr, Ba, Ra, and U from aquifer sediments under different temperature, salinity, and redox conditions. Broader Impacts: As analogues to surface estuaries, subterranean estuaries have high potential for significant geochemical transformations and so elucidating these mechanisms may have significant influence on understanding coastal groundwater geochemistry in other areas. While the overall importance of SGD on the global cycle of certain elements is uncertain at present, there is little doubt that SGD is important at the local scale both within the United States and throughout the world. Nutrient-rich (phosphate, nitrate, ammonium) groundwater, entering into coastal waters and bays, is not uncommon and represents an environmentally important component of SGD. Hence, improved understanding of the geochemical regime in subterranean estuaries has important water-quality implications for coastal aquifers and allows insights into fundamental biogeochemical reactions at a major freshwater/seawater interface. This project has an important educational component and seeks funding for a graduate student and an undergraduate who has worked on this project since high school outreach programs (lectures, posters) associated with the Waquoit Bay National Estuarine Research Reserve.