QUANTIFYING GROUNDWATER INPUTS TO EASTERN NORTH CAROLINA TIDAL CREEKS USING RADON TRACER

Tidal creeks especially those that drain permeable terrestrial upland watersheds, are hotspots for groundwater-surfacewater exchange and can influence the quantity and quality of water from both systems. Despite being a very common coastal feature in North Carolina, both volumetric water and dissolved contributions to coastal waters is less known. We quantified the net groundwater discharge in tidal creeks along the coastline of Wilmington NC using the natural groundwater tracer ²²²Rn. Initial survey results from a representative creek (Bradley Creek) showed radon in water concentrations from 52 Bq m^-3 to 198 Bq m^-3 during high and low tide events respectively. These generally high radon counts suggest high groundwater influx into the creek. Calculated groundwater discharge rates using ²²²Rn mass account for losses from offshore mixing range from 0.02 m d^-1 to 0.79 m d^-1 with an average flux of 0.41 m d^-1. These values account for an average of 38.5% of the tidal volume. Our initial results suggest that groundwater contributes a substantial amount of water and potentially associated dissolved materials to North Carolina coastal waters.