This project proposes to develop 223,224,228,226Ra isotope systematics to address the issue of groundwater flow into Florida Bay. Such methods are critical in accurately evaluating the role of submarine discharge and have direct implications for assessing coastal eutrophication, contamination and overall ecosystem change. Techniques proposed for this project have been successfully utilized to quantify the contribution of groundwater in coastal mixing on time scales of a few days to years. Briefly, radium has a very different geochemical signature in freshwater versus seawater. This attribute, in addition to known source functions, a wide range of half-lives (3.8 days to 1600 years), and elevated groundwater activities make radium ideal to examine subsurface water/sediment transitions. By measuring this suite of radium isotopes in local groundwater wells (which are already in place) as well as in surrounding fresh water, seawater and underlying limestone, the coastal groundwater discharge rate and magnitude will be determine. The application of radium isotopes in this system will provide vital information for establishing a comprehensive water and contaminant budget for Florida Bay.