Hydrogeologic Controls on Trace Metal and Nutrient Fluxes from Subterranean Estuaries

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

Despite being a major vector for the land-ocean transport of materials, the role of groundwater in oceanic elemental mass balances has been poorly characterized. And where groundwater has been explicitly considered, most studies have not quantified the importance of chemical transformations that occur during the mixing of meteoric water with saline pore water (the ?subterranean estuary?) prior to surface water discharge. In this study, researchers at the Woods Hole Oceanographic Institution will examine the importance of coastal hydrogeology on the flux of trace elements and nutrients from subterranean estuaries (STEs). In order to accurately quantify the impact of STEs on global biogeochemical cycles, they will investigate reactions in, and fluxes from, a wide range of coastal geomorphologies. The study will address the following key questions: 1. How does coastal hydrogeology influence the fluxes of trace elements into and out of subterranean estuaries? They will conduct a study of four STEs on the basis of their hydrological and geological characteristics: (1) karst (Yucatan Peninsula, Mexico); (2) fractured bedrock (Ubatuba, Brazil); and (3) ocean island ) volcanic and (b) carbonate platform (Guam). These sites were chosen to span a range of rock type, rainfall, and aquifer residence time. 2. What effect do these fluxes have on the mass balance of trace elements in the global ocean? In addition to sampling within the STE, the team will use radium isotopes and radon to quantify the flux of trace elements to the coastal ocean. By sampling each of these sites on a seasonal basis, they expect to scale the local fluxes to the global estimates using a coastal typology database. The potential broader impacts of this work are expected to be significant. Eutrophication due to anthropogenic nutrient enrichment is a global phenomenon and is arguably the greatest agent of change in coastal waters. This project will benefit society by helping to develop a better understanding of the behavior of groundwater transported trace metal and nutrients within a large proportion of coastal waters. The PI will actively involve undergraduate and high school students in this project, some from underrepresented groups. One full time Ph.D. student will be funded to work on this project. The proposed project offers a graduate student a variety of challenging research opportunities that cross traditional disciplinary boundaries such as hydrology, marine geochemistry and environmental analytical chemistry. Other broader impacts include collaboration with scientists from other countries. The outreach component of this proposal will involve the PI?s participation in the annual AmeriCorps water resource education training. AmeriCorps members participate in the Groundwater Guardians Water Festivals, which are held in middle school classrooms across Cape Cod, and involve several hands-on demonstrations designed to introduce students to all aspects of the water cycle on Cape Cod and the protection of water resources. In all, approximately 1800 students are expected to participate in this program each year. In addition to providing a training lecture to the volunteers, the PI will aid in the development of new submarine groundwater discharge teaching aid kits for this program.