Assessing Vegetation, Nutrient Content and Soil Dynamics Along a Coastal Elevation Gradient in a Mississippi Estuary

Coastal wetlands are one of the most valuable ecosystems; however, they have an uncertain future when faced with increasing sea-level rise (SLR) and both human-induced and environmental stressors. To better understand future marsh resiliency, we examined above- and belowground biomass, carbon (C), nitrogen (N), and phosphorus (P) tissue content and sediment characteristics along a coastal elevation gradient at the Grand Bay National Estuarine Research Reserve (GNDNERR). Vegetation and sediment characteristics were compared across several marsh types, and data was used to make updated predictions using the marsh equilibrium model (MEM). Standing and total biomass increased from 869 g/m2 and 4250 g/m2 respectively at low marsh sites to 2197 g/m2 and 6789 g/m2 at high marsh sites. N/P ratios increased from 10.25 to 20.43 from the low to high marsh, largely driven by decreasing P content in tissues. Spartina alterniflora and Juncus roemerianus biomass and tissue nutrient content were lower than other marshes in the northern Gulf of Mexico. Juncus roemerianus total biomass was around 50% of other coastal Mississippi locations. A meteorologically driven tidal regime and no major freshwater inflow could cause a lack of nutrient and sediment delivery to the marsh surface stunting total biomass and reducing accretion. Under various SLR rate scenarios, the MEM estimates that coastal wetlands at GNDNERR will undergo substantial changes within the next 50–100 years. The lack of nutrient and sediment delivery means that preserving coastal wetlands at GNDNERR will depend on aiding landward marsh migration.