Marsh migration changes the spatial patterns of plant communities across an estuary

Link To Share This Poster: https://cdmcd.co/v9DKrb

Molly Mitchell, VIMS, Gloucester Point, VA and Julie Herman, Center for Coastal Resources Management, Virginia Institute of Marine Science, Gloucester Point, VA

Background/Question/Methods
Tidal marshes are important ecological systems that are responding to sea level rise-driven changes in tidal regimes. As tidal marshes shift in response to sea level rise, the overall ecological structure of the estuary will also alter. Depending on their plant communities, tidal marshes provide different habitat, water quality, and carbon storage functions. Understanding the future distribution of the marshes allows us to predict changes in ecological function. To investigate shifts in estuarine ecological structure, we modeled the migration of marshes under sea level rise over the landscape of the Chesapeake Bay, VA, up to the tidal extent (including tidal freshwater communities). We included marsh plant community in the model to elucidate the effects of migration on different marsh types and to consider the impacts of changing marsh distribution on blue carbon storage.
Results/Conclusions
This study shows that in the Chesapeake Bay, USA, overall estuarine tidal marshes are projected to decline by approximately half over the next century. Tidal freshwater and oligohaline habitats, which are found in the upper reaches of the estuary and are typically backed by high elevation shorelines are particularly vulnerable. Due to their geological setting, losses of large extents of tidal freshwater habitat seem inevitable under sea level rise. In addition, saltwater intrusion into the upper reaches of creek systems will convert freshwater wetlands to saltwater, releasing carbon stored in the sediments. However, in the meso/poly/euhaline zones that (in passive margin estuaries) are typically low relief areas, tidal marshes are capable of undergoing expansion.
The overall loss of marsh acreage is concerning and will greatly affect the storage of blue carbon. Sediment released during front edge erosion or through the drowning of the front edge of the marsh will enter the estuarine system and be lost. Newly migrated marsh areas will take years to accumulate the depth of organic soils being lost under current accretion rates. The reduction of tidal freshwater marsh will reduce the amount of critical habitat available for anadromous fish and may impact populations, particularly in creek systems where freshwater marshes will be squeezed up into the headwater wetlands.