Soil carbon dioxide effluxes from riparian areas of two hydrogeomorphic settings in the Ozark National Forest, USA

Riparian buffers serve as conduits through which carbon (C) cycles from terrestrial landscapes to aquatic systems and, ultimately, to oceanic or atmospheric sinks. Riparian areas have also been identified as zones of concentrated biogeochemical activity that often produce greater amounts of greenhouse gases than neighboring upland terrestrial and adjacent aquatic systems. Little work has explored how hydrologic classification of a stream may influence the magnitude of riparian soil processes. A three-way factorial field study examined soil carbon dioxide (CO2) effluxes across flow regime (Groundwater and Runoff streams), season (autumn, winter, spring, and summer), and distance from stream edge (0, 10, and 20 m). Soil CO2 efflux differed between flow regimes across seasons (P = 0.01), where Runoff sites had greater spring soil surface CO2 efflux (i.e., soil respiration mean ± 1 SE = 2.98 ± 0.29 μmol CO2 m−2 s−1) than Groundwater sites (1.40 ± 0.30 μmol CO2 m−2 s−1). Soil CO2 effluxes from Runoff sites were related to soil temperature (rs value range = 0.58 to 0.82, all P < 0.0001) and soil moisture (rs value range = −0.35 to 0.27, P = 0.02 to 0.03). However, effluxes were unrelated to soil moisture at Groundwater sites. Results of this study suggest that consideration of the riparian zone and demonstrated differences in flow regime are needed to understand forested stream C budgets. Anthropogenic landscape alteration and climate change can modify the natural flow regime which, in turn, may have consequences for aquatic C dynamics in streams draining altered riparian zones, particularly in forested settings.