High-resolution observations of submarine groundwater discharge reveal the fine spatial and temporal scales of nutrient exposure on a coral reef: Faga'alu, AS

Submarine groundwater discharge (SGD) can deliver substantial nutrient and contaminant loads to nearshore coral reefs. Correctly scaling SGD rates from a point source to a reef is generally a linear process involving simplified assumptions on the hydrogeology, bathymetry, and nearshore hydrodynamics that are essential to properly assess SGD scale and impact to individual coral heads. Here, we apply high-resolution SGD techniques to provide information at the scale of individual coral heads in Faga’alu Bay, American Samoa, where focused SGD delivers a plume of freshened and nutrient-rich water directly to the adjacent coral reef. Unoccupied Aerial System-based measurements were used to acquire remotely sensed, calibrated, high-resolution thermal infrared imagery that were coupled with traditional in-situ SGD observations. This approach permits a detailed assessment of SGD and associated nutrient loadings to individual coral heads as a function of time and enables a more realistic method to quantify SGD impact.