Transitions from Freshwater Forested Wetland to Salt Marsh – Impacts of Sea Level Rise.

Saltwater intrusion due to sea level rise along the relatively flat southeastern US coastal plain significantly changes vegetation composition and soil and water chemistry of coastal wetlands, eventually modifying their ecosystem functions and biogeochemical processes. We collected monthly samples for two years to evaluate the dynamics and relationships among aboveground productivity, greenhouse gas emissions, nutrients, and dissolved organic matter of a freshwater forested wetland, a salt-impacted and degraded forested wetland, and a salt marsh in Winyah Bay, South Carolina, representing the salinity gradient and the transition from freshwater forested wetland to salt marsh due to sea level rise. High methane emission was only observed in the freshwater-forested wetland, but there was a strong smell of sulfide noticed in the salt marsh, suggesting that different redox processes control the decomposition of natural organic matter along the salinity gradient. The highest DOC concentration (28 - 42 mg/L) in monthly water samples was found in the degraded forest wetland, followed by the freshwater forested wetland (19 – 38 mg/L) and salt marsh (9 – 18 mg/L). The degraded forested wetland had significantly lower above-ground productivity with annual stem growth of 102 g/m^2/yr and litterfall of 392 g/m^2/yr compared to the freshwater forested wetland (230 and 612 g/m^2/yr, respectively). Results demonstrate that the salt-impacted degraded wetland has unique biogeochemical cycles that differ from unaltered freshwater forested wetland and salt marsh.