Opportunities and Challenges in Computing Fresh Groundwater Discharge to Continental Coastlines: A Multimodel Comparison for the United States Gulf and Atlantic Coasts

Abstract

AbstractThe fresh component of submarine groundwater discharge (fresh SGD) transports nutrient and contaminant loads from land to sea. Fresh SGD fluxes are poorly known but depend on geology, topography, climate, and land use. Here we assess two general approaches for quantifying the magnitude of fresh SGD over regional to continental scales—water budgets (lumped parameter models) and groundwater flow models—focusing on the U.S. Atlantic and Gulf Coasts as a large‐scale case study. Estimates of fresh SGD fluxes from groundwater flow models are more variable than estimates from water budgets, and both are often less than field‐based estimates. Both approaches predict the volume of fresh SGD within approximately 50% of 12.3 km3/year, in line with previous estimates, and differences are largely driven by hydrographic data inputs. The simplified water budget approach, while computationally cheap, cannot resolve flow paths or continuous flux distributions and may neglect groundwater flow from deep aquifers or distal recharge zones. Conversely, three‐dimensional groundwater flow models can resolve flow paths and fresh SGD contributions from heterogeneous aquifer systems but are computationally expensive and require more parameterization. Ultimately, multiple models and integrated field data are needed to improve our estimates of fresh SGD fluxes over a wide range of scales.