Integration of Aerial Thermal Infrared and Radon Surveys to Investigate Groundwater Discharge to Pearl Harbor, Oahu, Hawaii

The largest freshwater spring complex in the Hawaiian Islands discharges groundwater into Pearl Harbor via subaerial springs, submarine springs, and non-point source (diffuse) seepage. We used airborne thermal infrared remote sensing to map the spatial distribution and mixing of cold groundwater discharge throughout the harbor. We then conducted in situ surveys of the harbor's surface, intermediate, and bottom waters for radon-222, a tracer of groundwater discharge. We used these data to calculate groundwater discharge fluxes from radon and salinity mass-balance models. Our fresh groundwater flux estimates were comparable to estimates from published water budget models. Next, we multiplied the groundwater fluxes by representative nutrient concentrations in groundwater end-members from around the harbor. Compared to inputs from other Hawaiian coastlines, Pearl Harbor receives similar dissolved silica, nitrate, and orthophosphate loads on a shore-normalized basis from submarine groundwater discharge. By combining the thermal infrared and radon techniques, we produced linearly and highly correlated relationships between discharge plume areas and groundwater fluxes. Such relationships provide a way to up-scale local groundwater discharge and nutrient fluxes to regional scope.