man in red shirt riding yellow kayak on sea during daytime

Radon detector setup.USGS physical scientist Cordell Johnson installs a special buoy in the waters of the National Park of American Samoa on Ofu in the Manuʻa Islands Group, American Samoa. The special buoy, developed by USGS scientists, measures radon on the reef. Radon is a marker of submarine groundwater discharge that brings low-salinity waters, and sometimes nutrient- and contaminant-laden waters, to the coral reefs.