UTILITY OF RADON-222 AS A TRACER OF SUBMARINE GROUNDWATER DISCHARGE TO WAQUOIT BAY, MA

Quantification of submarine groundwater discharge (SGD) is of ecological interest since groundwater nutrient concentrations are often orders of magnitude higher than in receiving waters. Recent studies have popularized the use of radium and radon isotopes for assessing SGD to coastal waters. Radon-222 (half-life=3.8 d) is an ideal tracer of SGD in coastal settings because it occurs naturally in groundwater, is chemically conservative, and is orders of magnitude more concentrated in groundwater than seawater. Similarly, radium is naturally enriched in aquifer fluids and has four isotopes with half-lives ranging from 4 d to 1600 yr. The advantages of using chemical tracers such as 222-Rn and Ra isotopes include the ability to assess distribution and dispersion of SGD and associated nutrients in a coastal ecosystem. In Waquoit Bay, MA, SGD-derived nutrient fluxes will be traced using 222-Rn and radium activities of groundwater and bay water. A comparison of these two approaches will be carried out with data collected during summer 2001.