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

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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.