Modeling the Effects of Changes to Physical, Hydrological, and Biological Processes on Porewater Salinity Distributions in a Southeastern Salt Marsh

Coastal wetlands provide many important ecosystem services, which include carbon and nitrogen sequestration and transformations, the provision of habitats, and the reduction of erosion by the vegetation. Coastal wetlands will be affected by projected climate change and sea level rise and may fail to provide such services, prompting a need to understand the environmental controls on marsh and vegetation distribution. Therefore, as part of the Georgia Coastal Ecosystems Long Term Ecological Research project, an integrated modeling approach is being developed to simulate how changes in salinity and inundation may change marsh ecosystem services, by coupling a hydrodynamic with a soil and a plant model.

In coastal marsh ecosystems, porewater salinity strongly determines vegetation distribution and productivity. We will present the development of the soil model, which is based on mass conservation for water and salt and links physical, hydrological, and biological processes that determine porewater salinity, including precipitation, evapotranspiration, salt exchange between surface and subsurface, drainage, groundwater exchange, tidal inundation, and surface runoff, with the lateral exchange controlled by marsh topography.

The model is applied to the Duplin River marsh, Sapelo Island, Georgia. Model validation is performed by comparing model-estimated salinities to porewater salinity measurements taken in different vegetation classes and over a range of marsh elevations. Modeled variability in porewater salinities will be presented over spring-neap, seasonal, and annual time scales. To discuss potential impacts of climate change and sea level rise, a sensitivity analysis will be presented that demonstrates the effect precipitation intensity, evapotranspiration, permeability, and marsh elevation have on porewater salinities.