Temporal and microtopographical variations in greenhouse gas fluxes from riparian forest soils along headwater streams

Riparian zones of headwater streams have valuable ecosystem functions and are prevalent across many landscapes. Nevertheless, studies of greenhouse gas (GHG; CO2, CH4, N2O) fluxes from these unique ecosystems, with fluctuating water tables and high soil organic matter, remain limited. Our objectives were to (1) to quantify the effects of local riparian groundwater conditions on soil GHG flux rates, namely to determine if groundwater discharge (DIS) areas in the riparian zone would have higher soil moisture than adjacent non-discharge (ND) areas in the riparian zone, impacting GHG fluxes; and (2) to examine the relationship between GHG fluxes, soil moisture, soil temperature, and groundwater depth. We measured gas fluxes in situ alongside two relatively undisturbed headwater streams over 1 year, using closed static chambers and gas chromatography. We found that, although not significant, DIS areas had on average lower CH4 uptake and lower CO2 emissions than ND areas. We further found that soil temperature explained 30.0% and 26.2% of variation in CO2 and N2O fluxes, respectively, and soil moisture explained 9.8% of variation in CH4 fluxes. Our results provide information on the magnitude and drivers of GHG fluxes in riparian zones to help inform GHG budgets and forest management.