Ecology of Tidal Freshwater Forested Wetlands of the Southeastern United States

Science Center Objects

Tidal freshwater forested wetlands - TFFWs - can be found in the upper intertidal areas of many estuaries and act as a transition between coastal marshes and bottomland hardwood wetlands. However, it is because of their location that makes them vulnerable to sea-level rise, and they are constantly transitioning to different wetland types. USGS addresses how various processes are affected in TFFWs as they shift from a forest wetland state to a low-salinity marsh. 

Sampit River, SC, USA
Sampit River, South Carolina

The Science Issue and Relevance: Tidal freshwater forested wetlands (TFFWs) occur in upper intertidal reaches of many estuaries throughout the world, and represent a transition between coastal marshes and fluvial bottomland hardwood wetlands. Because of this landscape position, TFFWs are susceptible to sea-level rise and are constantly transitioning to different wetland community types over time scales of centuries to millennia. This project addresses how carbon, water, and biogeochemical processes are affected in TFFWs as they transition from a forested wetland state to an emergent, low-salinity marsh. Salinity is the primary driver of transitional changes along Atlantic and Gulf Coastal study locations. During previous research we have documented shifts in stand-level water use, increases in N and P mineralization, altered fluxes of greenhouse gas emissions from soils, changes in sediment inputs, and feedbacks to surface elevation loss as trees experience stress and die as forests transition to marsh. We also have determined some recovery in soil surface elevation as marshes take over.

Methodologies for Addressing the Issue: TFFWs take up nutrients, baffle water flows to induce sedimentation, sequester atmospheric carbon, support biodiversity, and provide barriers between terrestrial habitats (including human infrastructure) and aquatic environments during storms. In short, we measure as much of this directly as we can, and have been since 2005. While this project focuses on changes in soil and growth processes on 18 core study plots in South Carolina, Georgia, and Louisiana in a contemporary sense (decadal-scale), we also work with other USGS scientists to document Holocene habitat shifts (<6 ka) in TFFWs. Our overall project goal is to determine change in carbon budgets along the transition to marsh, and to link carbon, water, nutrient, and sediment budgets together as TFFWs are impacted in various ways and over different time scales by sea-level rise-induced salinization.

Future Steps: This project is actively expanding through other USGS collaborations to the Chesapeake Bay, and we will continue to advance our process-based understanding of how wetlands respond to salinity through new experiments. Expansion into new watersheds in the US and abroad is a likely future course.