Indian River Lagoon (IRL) is one of the most biologically diverse estuarine systems in the continental United States, extending 200 kilometers (km) along the Atlantic coast of central Florida. The lagoon is characterized by shallow, brackish waters with significant human development along both shores and a width that varies between 0.5-9.0 km.
Scientists from the U.S. Geological Survey (USGS) St. Petersburg Coastal and Marine Science Center, working in collaboration with the St. Johns River Water Management District, mapped surface water radon-222 (radon-in-water) and basic physical water column properties (for example, salinity and temperature) to examine submarine groundwater discharge at two locations, Eau Gallie North and Riverwalk Park, along the western shore of IRL. Eau Gallie North is near the central section of IRL while Riverwalk Park is approximately 20 km north of Eau Gallie site. At each study site, a radon mapping survey was performed over seven north-south shore parallel transects (EA-EG and RA-RG, respectively), positioned between 75-1000 meters offshore, and approximately 1.5 km in length. Each transect was mapped three times in an alternating north-south direction. Surface water was continuously pumped on-board into an air-water exchanger. Dissolved radon-222 was purged from the water into a gaseous phase inside the exchanger. Radon-222 in the exchanger was continuously pumped into and measured by commercially available radon-in-air detectors (RAD7, Durridge, Inc.). In situ surface water temperature and salinity, as well as the water temperature in the exchanger, were also measured. Radon-in-air measurements were corrected to radon-in-water activities using the temperature-salinity dependent air-water partitioning coefficient (Schubert and others, 2012). Starting in September 2016, the USGS conducted surveys bimonthly along the same transects to determine seasonal and temporal variability of radon-222. A previously published USGS data release (https://doi.org/10.5066/F7QF8S05) contains the raw radon-222 data and physical water column data collected from September 2016 through July 2017. The final survey, presented in this data release, was conducted during two separate time periods, one at each study site, instead of successively as in previous surveys, due to unfavorable weather conditions for radon-222 mapping. This data release contains the raw radon-222 data, physical water column data, Esri GIS data files and data distribution maps of the radon-222 activity and surface water salinity collected during the final IRL trips in September 2017 and November 2017.