Submarine groundwater discharge estimates at a Florida coastal site based on continuous radon measurements

The direct discharge of groundwater into thecoastal zone has received increased attentionin the last few years as it is now recognizedthat this process represents an importantpathway for material transport. Assessingthese material fluxes is difficult, as there isno simple means to gauge the water flux. Weestimated the changing flux of groundwaterdischarge into a coastal area in the northeastGulf of Mexico (Florida) based on continuousmeasurements of radon concentrations over aseveral day period. Changing radon inventorieswere converted to fluxes after accounting forlosses due to atmospheric evasion and mixing. Radon fluxes are then converted to groundwaterinflow rates by estimating the radonconcentration of the fluids discharging intothe study domain. Groundwater flow was also assessed via seepagemeters, radium isotopes, and modeling duringthis period as part of an ``intercomparison''study. The radon results suggest that the flowis: (1) highly variable with flows ranging from～5 to 50 cm/day; and (2) strongly influenced bythe tides, with spikes in the flow every 12hours. The discharge estimates and pattern offlow derived from the radon model matches theautomated seepage meter records very closely.