Impact of sea level rise on chloroform and methane emissions from a forested degraded wetland in coastal South Carolina

Intrusion of seawater into coastal freshwater wetlands in the southeastern United States is increasing due to tropical storms and sea level rise, resulting in a dynamic landscape where freshwater forest is converted to degraded forest/wetland. The biogeochemical consequence is that haloform and methane emissions from this ecosystem can be dramatically altered. Haloforms include bromoform and chloroform, and these volatile organic compounds can contribute to stratospheric ozone depletion. However, their emission patterns are highly irregular, leading to significant questions regarding their overall emissions and their production mechanisms. In the degraded wetland, chloroform emissions are higher and methane emissions are lower than the unaltered freshwater wetland, suggesting an important biogeochemical shift in the transformation processes of soil carbon. We conducted bi-monthly field measurements of halocarbon and greenhouse gas emissions from a degraded wetland in coastal South Carolina over the past year. Three sites were chosen to identify the temporal variability of fluxes and the impact of visible light and dark incubations on halocarbon and greenhouse gas formation. Results demonstrated that the same site can have significant day to day variation, but the emission rates are not clearly related to light exposure. The present research also shows a much larger chloroform emission rate than previously reported for similar environments. Methyl halide emissions were also measured, but this ecosystem was not a significant source of this compound and shifted to a sink during drier conditions.