Greenhouse Gas Emissions and Denitrification within Depressional Wetlands of the Southeastern US Coastal Plain in an Agricultural Landscape

Abstract

Carolina Bays are depressional wetlands on the Coastal Plain of the southeastern United States. These wetlands are often the recipient of nutrient runoff from adjacent agricultural lands and there is potential for production of greenhouse gases during nitrification and denitrification processes occurring in the wetland sediments. Because of their saturated conditions, Carolina Bays may improve regional water quality through denitrification of soil nitrate. Three small bays in South Carolina were selected for denitrification and greenhouse gas analysis. A transect of four points was sampled within each Carolina Bay in May, July, September, and November over a two year period. Gas emissions were measured in-situ using a photoacoustic gas analyzer and soil samples were brought back to the lab for denitrification enzyme activity and microbial analysis. Emissions of nitrous oxide (N2O) averaged 1.8 mg m−2 d−1, with a median of 0.47 (with a range of below detectable limits to 9.414 mg m−2 d−1). Many measurement events of N2O were below detection and did not vary within the bays. The carbon dioxide emissions from Carolina Bays averaged 15.8 g m−2 d−1 and were largely controlled by temperature. Denitrification enzyme activity had a larger response to nitrate additions further into the bays. Gram + bacteria were also greater deeper into the bays, while Gram- and fungal populations were greater at the field/wetland interface. Manure application had some minor effects on DEA within the bays, but did not appear to increase gas emissions over the period measured.