Using local scale 222Rn data to calibrate large scale SGD numerical modeling along the Alabama coastline

Current Earth System Models (ESM) do not include groundwater as a transport mechanism of land-born constituent to the ocean. However, coastal hydrogeological studies from the last two decades indicate that significant material fluxes have been transported from land to the continental shelf via submarine groundwater discharge (SGD). Constructing realistic large-scale models to assess water and constituent fluxes to coastal areas is fundamental. This paper demonstrates how an independent tracer groundwater tracer approach (based on ²²²Rn) applied to small scale aquifer system can be used to improve the precision of a larger scale numerical model along the Alabama coastline. Presented here is a case study from the Alabama coastline in the northern Gulf of Mexico (GOM). A simple field technique was used to obtain groundwater seepage (2.4 cm/day) to a small near shore lake, representative to the shallow coastal aquifer. These data were then converted in site-specific hydraulic conductivity (23 m/day) using Darcy’s Law and further incorporated into a numerical regional groundwater flow model (MODFLOW/SEAWAT) to improve total SGD flow estimates to GOM. Given the growing awareness of the importance of SGD for material fluxes into the ocean, better calibrations of the regional scale models is critical for realistic forecasts on the potential impacts of climate change and anthropogenic activities.