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The St. Petersburg Coastal and Marine Science Center’s Estuarine and MaRsh Geology (EMRG) group published a new USGS geonarrative on the extensive research that has taken place in Grand Bay, Mississippi and Alabama over the past nine years.

Animation shows tides washing away brown mud from the shoreline and eroding green marshgrass. A graph follows the tide.
Salt marshes provide important economic and ecologic services but are vulnerable to habitat loss, particularly due to shoreline erosion from storms and sea level rise. Sediments eroded at the marsh edge are either delivered onto the marsh platform or into the estuary, the latter resulting in a net loss to the marsh sediment budget and released soil carbon. Knowledge on the timing, distance, and quantity of sediment deposition versus shoreline erosion along the marsh-estuary interface is critical for evaluating the overall health and vulnerability of coastal marshes to future scenarios of sea level rise and storms. This image is a depiction of what happens to sediments as they are eroded at the marsh edge, delivered into the estuary and onto the marsh platform, leading to a higher marsh platform elevation at the marsh shoreline, but loss of wetland habitat area at the eroding shoreline edge.

Over the past few centuries, Grand Bay, located along the northern Gulf of Mexico, has been impacted by the avulsion of the Escawapa River, large storm events, and the erosion of Grand Batture Island. To assess the past and future environmental impact of these changes, SPCMSC researchers have spent the last nine years assessing the effects of storms, sea-level rise, and restoration activities in Grand Bay. To address those goals, current and past long-term change and short-term variability studies have focused on digitizing historical maps of the area, calculating historical and modern shoreline change rates, generating bathymetric maps based on historical maps and modern data, and collecting surficial and downcore sediment samples. Surficial and downcore sediment samples are used to calculate seasonal and long-term (centurial) sediment accumulation rates, generate regional distribution maps, and assess sediment source through the use of multiple proxies including sediment characteristics, and foraminiferal and diatom biofacies. Accurate historical and modern maps and sedimentation rates can be fed into a variety of different numerical models to evaluate model efficacy and the impact of future coastal erosion hazards or environmental change, and inform managers on the predicted impacts of various restoration efforts.

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