CARBON DIOXIDE, NITROUS OXIDE AND METHANE FLUXES FROM AGRICULTURAL SOILS

Rising atmospheric concentrations of carbon dioxide [CO₂], methane [CH₄], and nitrous oxide [N₂O] are partly responsible for the increase in average global surface temperatures. How much warming can be attributed to greenhouse gas emissions from constructed wetlands is largely unknown. We examined the fluxes of CO₂, CH₄, and N₂O in agricultural soils in southwest Ohio, prior to wetland restoration. Using the static-headspace chamber method, we measured fluxes from 40 chambers on 30 days from June through December 2010. Ancillary measures of soil moisture content and inorganic nitrogen (nitrate and ammonium) were compared to understand the potential controls on gas fluxes. Fluxes of CO₂ were greatest in early summer and began to decline in late summer. N₂O fluxes slowly declined from June through September. Because summer 2010 was quite dry, soil moisture also declined during the same period, before rewetting in late fall. These results suggest that greenhouse gas fluxes from agricultural lands are affected, in part, by soil moisture content, which can vary substantially inter-annually.