ORIGINAL RESEARCH Greenhouse Gas Emissions and Denitrification within Depressional Wetlands of the Southeastern US Coastal Plain in an Agricultural Landscape Jarrod O. Miller 1 & Thomas F. Ducey 1 & P. William Brigman 1 & Charlie O. Ogg 1 & Patrick G. Hunt 1 Received: 5 May 2016 /Accepted: 30 September 2016 /Published online: 17 October 2016 Abstract Carolina Bays are depressional wetlands on the Coastal Plain of the southeastern United States. These wet- lands are often the recipient of nutrient runoff from adjacent agricultural lands and there is potential for production of greenhouse gases during nitrification and denitrification pro- cesses 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 en- zyme activity and microbial analysis. Emissions of nitrous oxide (N 2 O) 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 N 2 O were below detection and did not vary within the bays. The carbon dioxide emis- sions from Carolina Bays averaged 15.8 g m -2 d -1 and were largely controlled by temperature. Denitrification enzyme ac- tivity 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. Keywords Carolina bays . Denitrification . PLFA . DEA . Photoacoustic gas analysis . PAGA Introduction Carolina Bays are depressional wetlands on the South Atlantic Coastal Plain of the United States, with a water cycle largely dependent on precipitation (Newman and Schalles 1990; Lide et al. 1995; Bruland et al. 2003; Sharitz 2003). While rainfall and evaporation dominate inputs into these wetlands, ground and surface water from adjacent uplands also flows through Carolina Bays (Sun et al. 2006). Water inputs from uplands are governed by topography as well as the presence of restric- tive layers beneath the landscape (Sun et al. 2006). Because of the variability in water inputs, these wetlands may have dif- ferent hydrologic regimes, with some being consistently drier than others (Lide et al. 1995; Sharitz 2003). Carolina Bays also have a large range in size, with some bays being greater than 3000 ha, but most others less than 1 ha (Sharitz 2003). Many of the smaller bays have been drained for agricultural use (Kirkman et al. 1996; Bruland et al. 2003; Sharitz 2003), but have demonstrated the ability to return to a forested state (Kirkman et al. 1996; Bruland et al. 2003). Soils within Carolina Bays can be composed of organic or mineral materials, and are often underlain by sandy or clay layers (Sharitz 2003; Caldwell et al. 2007). Mineral soils are more likely to be found inland, while those bays near the coast are more likely to consist of peat materials (Newman and Schalles 1990; Sharitz 2003). Soil characteristics of surface horizons will vary as they move towards the center of the bays. Reese and Moorehead (1996) have reported thicker A horizons at the rim, while pH, bases (Ca, Mg, K), and sand content typically increase towards the center of the bays. * Thomas F. Ducey Thomas.Ducey@ars.usda.gov 1 ARS-USDA, Coastal Plains Soil, Water, and Plant Research Center, 2611 W. Lucas St, Florence, SC 29501, USA Wetlands (2017) 37:33–43 DOI 10.1007/s13157-016-0837-5 # Society of Wetland Scientists (outside the USA) 2016