Global climate change is predicted to cause extensive changes in the earth's ecosystems. Sea level rise (SLR) currently averages 3 mm yr-1, but is expected to accelerate over the coming century. Some of the habitats most vulnerable to SLR are tidal wetlands, which exist at the interface between land and sea. Decades of research at the Georgia Coastal Ecosystems (GCE) LTER has shown that coastal wetlands provide important ecosystems services such as wildlife habitat, carbon sequestration, and water quality improvements, especially the removal of nitrogen from coastal waters.
A series of long-term studies conducted by researchers at the GCE showed that SLR and the subsequent intrusion of seawater into freshwater wetlands will dramatically alter the wetland landscape in coastal Georgia and the important services that they provide. With funding from the GCE, the U.S. Environmental Protection Agency’s STAR [in full??] program and the U.S. Department of Energy’s NICCR [in full??] program, researchers employed a combination of field, laboratory and modeling techniques to predict how tidal wetlands will be affected by accelerated SLR and saltwater intrusion. Model simulations based on the Intergovernmental Panel on Climate Change A1B Maximum Scenario, performed with the Sea Level Affects Marshes Model, predicted that overall wetland area will decrease by as much as 33% by 2100, but these differences were uneven, with a decline in salt marsh area of 45% as they convert to open water, and a decline of 39% in freshwater marsh. The loss of freshwater wetlands will be particularly bleak for endemic species like the American alligator and the wood stork. In contrast, brackish marsh area will only decline by 1% as they migrate inland and replace former freshwater habitats.
The researchers also documented substantial differences in terms of the services provided by different wetland types: biomass production, which is important for habitat provision and carbon sequestration, was 50% higher in fresh and brackish marshes than in salt marshes.
Nitrogen accumulation and denitrification rates, indicative of a wetland's ability to remove nitrogen from coastal waters, were more than 3 times higher in fresh and brackish marshes. Although sea level rise will lead to marsh loss in the coming century, the finding that brackish marshes provide ecosystem services at equivalent or higher rates than other marsh types, combined with the prediction that they will see little reduction in area, suggests that they may moderate the decline in ecosystem services.
Currently, GCE scientists are working to integrate long-term records of salinity and discharge from Georgia rivers into modeling efforts and investigate mechanisms that may compound the effects of SLR. For example, reduced freshwater and sediment inputs can lower accretion rates in marshes, and increases in salinity in freshwater wetland soils due to salt water intrusion can cause the release of sequestered carbon from these sediments, resulting in the collapse and submergence of freshwater soils.
This research is especially important to wilderness and wildlife management agencies, as it indicates the importance of protecting habitat that will be occupied by brackish and freshwater marshes as sea level rises.