Wetlands are one of the most valuable ecosystems, providing services such as carbon sequestration and nitrogen removal. Studies suggest that created wetlands may not function the same as natural wetlands and management techniques, such as organic matter addition (OM), have been proposed to promote natural functions. The objective of this study was to understand the effects of OM additions on greenhouse gas (GHG) emissions in created wetlands with different vegetation, hydrology and soil characteristics. This study was conducted from 2016 to 2017 at two created wetlands (A2S and A3A) at High Acres Nature Area in Fairport, New York. There was high seasonal and inter-annual variability in weather conditions during the study period and rainfall and temperature were the dominant factors controlling GHG fluxes within both wetlands. Drought condition during 2016 limited soil respiration and C uptake by plants. In 2017, when moisture conditions were more typical, OM addition increased soil respiration rates at A2S in the fall. There was a trend towards higher ecosystem respiration at this time; however, OM addition also increased gross primary production, resulting in no net change in CO2 exchange. Due to dry conditions, methane (CH4) emissions were low during much of the study. When emissions were high, fluxes were significantly higher in the light than the dark at A2S, but not A3A, suggesting that vegetation differences between the site impact CH4 transport pathways. While OM addition did not change anaerobic CH4 or CO2 production potential, there were significant differences between the sites, with higher production rates in A2S, where hydrologic conditions in the field may have selected for microbial communities adapted to anaerobic environments. These findings highlight the importance of precipitation and hydrology in controlling C cycling in created wetlands and suggest that wetland characteristics will influence their responses to management techniques
