INTEGRATED INVESTIGATION OF SUBMARINE GROUNDWATER DISCHARGE PROCESS AND CHEMICAL FLUX INTO THE OCEAN USING UNMANNED AERIAL VEHICLE (UAV)-THERMAL INFRARED (TIR) MAPPING AND IN-SITU MEASUREMENT DATA

Submarine groundwater discharge (SGD) is a global phenomenon that carries large volumes of groundwater and chemical species into the ocean. Despite its importance, lack of tools to assess SGD’s spatial and temporal variability has hampered deeper understanding of the process and its implications in global water and elemental cycles. Here we report the spatial and temporal variations of SGD flux and chemical flux into a coastal water of Jeju Island, Korea, based on aerial surveys with an unmanned aerial vehicle (UAV) equipped with a thermal infrared (TIR) system complemented by field investigations. This is the first work to report successful acquisition of SGD plume imagery using a UAV. We observed strong thermal signatures of SGD plumes along the coastline of the study site. Multiple UAV aerial surveys clearly captured dynamics in sea surface temperature (SST) driven by temporal variability of SGD, with greatly improved resolutions in SST maps compared to those obtained using heavy aircrafts. SGD flux estimated assuming a linear relationship between SGD flux and plume area relation ranged from 800-1300 m3/h during high tide to 2300-3300 during low tide. Based on the estimated SGD rates and measured concentrations, we appraised the loads to the coastal system of dissolved inorganic nitrogen (DIN), maximum dissolved inorganic phosphorous (DIP), and silica at 20-40, 0.2, and 32-60 mole/d/m, respectively. Our observations highlight that TIR mapping using a UAV can serve as one of the most powerful tools in studying SGD and other coastal processes.