Human accelerated climate change will alter the functioning of coastal plain wetlands through changes in hydrology and sea level rise. Decreased precipitation and sea level rise will increase the probability of saltwater intrusion into formerly freshwater wetlands. While much work has been conducted on the effects of saltwater intrusion on wetland vegetation, much less is known about the effects on biogeochemical cycling of carbon (C), nitrogen (N), and phosphorus (P). Saltwater intrusion can alter biogeochemical cycling of C, N, and P through both microbial metabolic and physicochemical pathways. Microbial metabolic pathways are due to changes in the availability of electron donors and acceptors. Physicochemical pathways are due to changes in chemical equilibrium, flocculation, and cation exchange with sediments. The main objective is to examine the effects of saltwater intrusion on C, N, and P cycling in coastal plain wetlands. The overarching hypothesis is that saltwater intrusion will increase N and P availability, while decreasing C availability, primarily through physicochemical pathways. The work will be conducted in the Timberlake Observatory for Wetland Restoration (TOWeR) site, a large (440 ha) extensively instrumented wetland restoration project in the coastal plain of North Carolina. The temporal and spatial dynamics of saltwater intrusion into the site provide unique opportunities to test the consequences of saltwater on biogeochemical cycling.
The functioning of coastal plain wetlands will change due to alterations in hydrology and sea level rise. Decreased rainfall and sea level rise will increase the probability of saltwater intrusion into formerly freshwater wetlands. While much work has been conducted on the effects of saltwater intrusion on wetland vegetation, much less is known about the effects on biogeochemical cycling of. Saltwater intrusion can alter the cycling of carbon (C), nitrogen (N), and phosphorus (P) in the wetlands. The research proposed will illuminate vital aspects of the coupling of C, N, and P cycles in coastal plain wetlands under saltwater intrusion. The ability to predict how these ecosystems respond to altered precipitation regimes and sea level rise will depend on understanding both the microbial metabolic as well as the physicochemical effects of saltwater on ecosystem function. This work provides a unique opportunity for basic ecosystem ecology research to have a direct impact on the regulations and practice of wetland restoration.
Saltwater incursion into former freshwater wetland ecosystems is likely to become more common due to human activities and sea-level rise. Much research has focused on how saltwater incursion alters wetland plant communities, but less work has examined how it might change the capacity of wetlands to provide clean water. In this project we studied the consequences of saltwater incursion on the capacity of wetlands to remove nitrogen and phosphorus, common pollutants that decrease water quality. We found that seasonal saltwater incursion lead to increased export of nitrogen from two natural wetlands and a restored wetland. The increase in nitrogen export was highest from the restored wetland, probably due to the effects of past fertilizer application (Ardón et al. 2013). We also examined how salinity affected dissolved organic carbon in the water. We found major declines in dissolved organic carbon, and changes in composition of dissolved organic matter. Overall our results indicate that increased salinity in freshwater wetlands can have major impacts on water quality, which means that changes in drought and storms, associated with climate change, and sea-level rise could lead to further deterioration of water quality reaching sensitive coastal waters. The intellectual merits of this project included increasing our understanding of the links between water quality and increased salinity. It also provided information of an unforeseen consequence of wetland restoration. Restoration of the hydrologic connectivity to the Albemarle Sound, facilitated saltwater incursion during drought years to a site that probably had not experienced salinity in at least two decades. The broader impacts of this project included advancing the career of a young investigator that is part of an under-represented group, as well as supporting two masters’ theses and one undergraduate research student. Results from this project were presented at two national meetings and used in two academic courses (Wetland Ecology and Management and Restoration Ecology) taught at East Carolina University. References Ardón M., J.L. Morse, B.P. Colman, and E.S. Bernhard. 2013. Drought-induced saltwater incursion leads to increased wetland nitrogen export. Global Change Biology 19: 2976-2985.
