Collaborative Research: Chemistry of Groundwater Transport Pathways Associated with a Coastal Lagoon System

根据该奖项，研究将侧重于了解可渗透沉积物中的反应和运输路径，并将试图确定营养物质和其他微量物质在连接巴西泻湖和邻近海洋的地下淡水-海水混合区中是如何运输和修改的。这项研究还将评估水文强迫条件如何改变这些过程。油田区域是巴西最南端海岸上毗邻帕托斯泻湖的屏障口岸。之所以选择这个地点，是因为：1)PI初步结果表明，该地区有利于海底地下水排放(SGD)，他们预计会有大的化学信号和交换率。2)相对不受人类活动的影响。3)有两个Ilter项目专注于这个系统，4)这个系统与美国东南海岸形成了鲜明的对比。这项研究将确定相关的反应，并估计营养物质和微量元素的通量(使用镭同位素)。如果可渗透沉积物是感兴趣物质的重要来源或汇，哪些反应路径控制它们在沉积物中的行为，以及过程如何受到外部强迫(主要是泻湖水位)的影响，PI将确定。该项目包括三个部分：1)实地活动，2)实验室动力学实验，3)通过定性和定量分析以及简单的数值模拟综合结果。实地工作将涉及在屏障口岸和海洋一侧的海滩上放置井，部署海底暗室，以及沿海巡航，后者建立近海Re同位素梯度，以评估SGD通量。实验室研究将使用流动塞式反应堆中的岩芯切割，以更好地评估反应的性质和动力学。最后，数值模拟将被用来帮助解释结果。

Under this award, study will focus on understanding of reaction and transport pathways in permeable sediments and will attempt to determine how nutrients and other trace substances are transported and modified in the subterranean freshwater-seawater mixing zone connecting a Brazilian lagoon to the adjacent ocean. The study will also evaluate how these processes are altered by hydrologic forcing conditions. The field area is the barrier spit adjacent to the Patos Lagoon on the extreme southern coast of Brazil. This site was chosen because: 1) the PIs preliminary results demonstrate that this region is favorable to Submarine Groundwater Discharge (SGD) and they anticipate large chemical signals and exchange rates. 2) it is relatively unimpacted by human activity. 3) there are two ILTER Programs focused on this system, and 4) this system provides a contrast to the southeastern US coast. This study will identify relevant reactions and estimate the fluxes of nutrients and trace elements (using radium isotopes). The PIs will detenrnine if permeable sediments are a significant source or sink for the materials of interest, which reaction pathways control their behavior in the sediments, and how processes are affected by external forcing (primarily lagoon water level). The project has three components: 1) field campaigns, 2) laboratory kinetic experiments, and 3) synthesis of results through qualitative and quantitative analyses and simple numerical simulations. Field work will involve placement of wells both across the barrier spit and along the beach on the ocean side, benthic chamber deployments, and coastal cruises, the latter to establish offshore gradients of radium isotopes to assess SGD fluxes. Laboratory studies will use core cuttings in flow-through plug reactors to assess better the nature and kinetics of reactions. And finally, numerical simulations will be used to aid in interpreting results.