​​​​​​​A balancing act: Project travels up estuaries to find tipping points

Four-year grant connects marsh health with local economics and environmental impact

The forces at work in a marsh require a delicate balancing act.

Rising and falling tidewaters keep clumps of Spartina grasses from growing too dense. But too much water makes it difficult for them to survive. Tip this balance too far in either direction and the marsh ecosystem collapses, resulting in a population of different plants—or no plants at all.

We know a lot about this process in salt marshes. But as you travel farther away from the shore, venturing into brackish and even freshwater marshes, there’s less we know about how these systems stay healthy. Now, a new grant will help University of Georgia scientists delve into the dynamics of these wetlands, including how collapsing marshes can affect property values and storm resiliency in coastal communities.

“We’re taking an existing mathematical model that’s out there for salt marshes and moving it up into brackish and freshwater marshes, which have different vegetation and different soils,” said Lori Sutter, research scientist at the University of Georgia Warnell School of Forestry and Natural Resources and principal investigator on a new four-year, $1.5 million grant from the National Oceanic and Atmospheric Administration. “And, we want to use what we know about how long a marsh will be able to stay at a high enough vertical space to keep up with sea-level rise.”

The project is one of five new projects across the country aimed at addressing the complex challenges of sea level rise. The full list of projects is available online.

Using a biophysical feedback model, the Marsh Equilibrium Model, Sutter and colleagues from University of South Carolina and Villanova University will be able to more realistically predict interactions between soil, plants and water level in tidal marshes. Those results will be incorporated into a flooding model called the Sea Level Affecting Marshes Model, or SLAMM, which the team will apply to marsh areas in Georgia, South Carolina and the Delaware Bay. Once they determine wetland areas that will likely flood, the team will incorporate various scenarios of rising sea levels.

From there, the results will point to how the sea level changes affect marsh health—as well as the economic impact that flooding could have on property values. Healthy marshes help prevent storm surge and flooding, but when that delicate balance in a marsh has been tipped, its protections are decreased.

The project incorporates UGA expertise from environmental economist Yukiko Hashida in UGA’s College of Agricultural and Environmental Sciences, as well as researchers in Franklin College of Arts and Sciences department of geography. In the end, the team plans to create maps of imperiled inland marshes and property that could be affected by the loss of the flooding protection these wetlands provide—along with a pathway to shoring up marshes to mitigate extensive property damage.

“So, local managers or even the public could say, in theory, ‘Gosh, it looks like, under this scenario that’s likely to happen in 20 years, we’re going to lose $10 million in buildings in this part of the world,’” said Sutter. “But if we fix this area of the marsh that’s degraded—maybe if we do a bit of planting years in advance—maybe we could offer some protection and we’d only lose $500,000.”

By pointing out places where marshes can be improved, added Sutter, coastal managers and city officials can pinpoint the best places to invest. Small changes now could add up to big savings down the road, as coastal storms begin to increase in intensity and sea levels creep higher.

“A lot of what we know about salt marsh ecology has come out of Georgia,” she said. “I’ve spent many years working in these areas to predict what’s going to happen, and some of this work suggests that unless we do some work to plan proactively, some marshes are going to turn into mud flats.”