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GCE III - Key Finding in 2019

    Groundwater discharge increases with marsh inundation

    Groundwater can be an important source of freshwater and nutrients to coastal waters. However, flow within salt marsh sediments is complex and is affected by plant zonation as well as variation in tidal forcing over daily, monthly, seasonal, and annual scales (Wilson et al. 2015a, b). Peterson et al. 2019 used a combination of field observations and modeling to quantify groundwater inputs into the Duplin River from the intertidal marshes of Sapelo Island. They used a radon mass balance approach (Fig. 1; see also Moore et al. 2006) and found that groundwater discharge increases with the aerial extent of marsh inundation. This conclusion is important for understanding how salt marsh circulation will respond to increased inundation from rising sea levels or reduced sediment supply. This quantification of volumetric water flow is being used to constrain our hydrodynamic model, and it lays the foundation for estimating nutrient fluxes from the subsurface to the receiving surface waters.


    Fig. 1 Schematic of the radon box model. The radon box model considers changes in total radon activity in the main channel (between site A and B) as well as in the headwaters (upstream of site B) to be a function of variable input sources (+; production from decay of parent 226Ra [P], river transport into the box [Qin], and groundwater discharge [Qgw]) and output sinks (-; decay [D], atmospheric evasion [Jarm], current evasion [Jcurrent], and river transport out of the box [Qout]). From Peterson et al. 2019.


This material is based upon work supported by the National Science Foundation under grants OCE-9982133, OCE-0620959, OCE-1237140 and OCE-1832178. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.