Camille Stagg, a USGS research ecologist who led the study titled “Accelerating elevation gain indicates land loss associated with erosion in Mississippi River Deltaic Plain tidal wetlands,” explained that this information sheds new light on the way researchers study wetland loss. 

Wetlands are a vital wildlife habitat for thousands of species and provide flood protection by buffering land from storms, among other functions.

In recent years, the Mississippi River Delta has experienced the highest rates of wetland loss in the United States.  Costal Louisiana alone has lost more than 2,000 square miles of land from 1932 to 2016, according to USGS research, and subsidence, or decreasing elevation, is most commonly cited as the cause of this loss.

However, while Stagg’s study notes edge erosion, or receding marsh, as a leading cause of coastal wetland loss in this region, it also found that sites with the most land loss exhibited accelerating elevation gain. 

This wetland loss phenomenon has also been observed in Grand Bay, Mississippi, documented in a 2021-released study by USGS research ecologist Kathryn Smith. A follow-up study published this year, led by USGS scientist Alisha Ellis with co-authors Christopher Smith and Kathryn Smith, suggests this process has been operating over many years.

Stagg’s study shows the prevalence of this process and links it to land loss through the use of satellite imagery. 

This is a surprising finding that provides a new, multidimensional way of thinking about wetland loss, said Stagg, explaining that it can be used to provide more accurate wetland vulnerability assessments. 

In this process the shoreline of a wetland is eroded by waves or currents eating away the sediment along the edge of the wetland. The displaced sediment is then deposited back onto the wetland platform by other waves. When this process happens continually, layers of displaced sediment build up over time, raising the surface of the wetland. This process ultimately leads to both elevation gain and land loss at the same time. 

“This is an exciting finding for us, as it gives us a new indicator for wetland loss and provides a more wholistic view of how these systems are changing,” Stagg said. “By coupling elevation change data with satellite-acquired land loss data, we can gain a better understanding of what is causing land loss.”

For more detailed information on wetland research at the USGS, please visit https://www.usgs.gov/centers/wetland-and-aquatic-research-center/science/priority-landscape or https://geonarrative.usgs.gov/grandbay/. 

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