Spatiotemporal Variability of Carbon Dioxide and Methane Fluxes in Six Temperate Wetlands

Wetlands are important to global carbon cycling, emitting large amounts of the greenhouse gas (GHG) methane (CH4) and acting as sources or sinks of carbon dioxide (CO2). Yet, wetland GHG fluxes are uncertain due to spatiotemporal variability among and within wetlands and multiple environmental factors influencing fluxes. To address these sources of uncertainty, we studied six wetlands representing three wetland types (bog, emergent, and forested) in Central New York (USA) from June to November. We measured CO2 and CH4 fluxes and environmental parameters related to porewater, hydrology, temperature, and vegetation. GHG fluxes differed over time across the wetland types, with CO2 fluxes ranging from -30.31 to 30.85 and CH4 fluxes from -0.18 to 31.20 mmol m−2 h−1. For CO2, emergent wetlands were sinks in June and emitted the most in July, forested wetlands showed consistent emissions over time, and bogs switched between sources and sinks, with highest emissions in July. For CH4, emergent wetlands had the greatest fluxes in July, bogs had similarly variable fluxes over time, and forested wetlands had consistently low fluxes. Within a wetland, spatial variability exceeded temporal variability for CO2 fluxes but was similar to temporal variability for CH4 fluxes. Warmer porewater temperatures increased CO2 and CH4 fluxes, and CH4 fluxes positively related to standing water depth. Overall, wetland GHG fluxes varied among wetland types within one region, with idiosyncratic variation across time and space, suggesting that including local vegetation and temporal variability may reduce uncertainty in upscaled models of wetland GHG fluxes.