SPATIAL AND TEMPORAL PATTERNS OF CO2, CH4, AND N2O FLUXES AT THE SOIL-ATMOSPHERE INTERFACE IN A FORESTED WATERSHED OF THE US NORTHEAST

Forest soils are recognized as sinks and sources of greenhouse gases (GHG) (CO₂, CH₄, and N₂O), but there is limited data quantifying the magnitude of GHG fluxes at the soil-atmosphere interface across large spatial and temporal scales and across various landscape geomorphic classes (e.g. wetlands, riparian zones, hillslope, etc). In this study, GHG fluxes were measured in a forested watershed comprised of wetlands, lowlands, upper hillslopes, lower hillslopes, riparian zones, and headwater wetland sites, and evaluated in relation to changing temperature, antecedent flow conditions, and stream chemistry between 2011 and 2013. Average study period CO₂ fluxes were positive at all locations and ranged between 0.61-2.89 g C m^-2 d^-1, with the larger fluxes occurring in well-drained soils. Average study period CH₄ fluxes ranged from -2.53 to 330.34 mg C m^-2 d^-1. Negative fluxes (indicating CH₄ sinks) were found at the hillslope and lowland sites, whilst the wetland was a hot spot for CH₄ emissions. Average study period N₂O fluxes ranged between -0.72 to 0.70 mg N m^-2 d^-1. Spearman correlation coefficients indicated a significant positive relationship between CO₂ efflux and soil temperature at each sampling site. With a few exceptions, no significant correlation was observed between CH₄ or N₂O and either temperature, antecedent flow conditions, or water quality. However, GHG fluxes were related to major landscape geomorphic classes suggesting that landscape position was a primary driver of overall GHG emission during the study period.