Emissions and dynamics of N2O in a buffer wetland receiving water flows from a forested peatland

Saari, P., Saarnio, S., Heinonen, J. & Alm, J. 2013: Emissions and dynamics of N2O in a buffer wetland receiving water flows from a forested peatland. Boreal Env. Res. 18: 164-180. Forestry operations can cause disturbances in nutrient cycling. Protection of watercourses by trapping the leached solids and nutrients in sedimentation ponds and buffer zones may create a new greenhouse gases (GHG) source. We measured in situ nitrous oxide (N2O) fluxes in different parts of a spruce swamp buffer zone, N2O emissions from intact peat columns after fertilization with different ammonium nitrate (NH4NO3) levels, and the rate and volume of in vivo N2O accumulation. N2O-producing micro-organisms existed throughout the buffer zone. The rate of N2O formation was highest at depths close to the prevailing water table within the buffer zone. Groundwater level and the vicinity of bypass water flows at the soil surface regulated the spatial and temporal variation in the rate of N2O efflux in the field. Nitrogen (N) addition rapidly increased in vivo N2O release. Microbial activity in the laboratory incubations under optimal conditions was high, but the in situ N2O efflux in the field was low. The actual leaching of mineral N from forestry areas was low and the inorganic N concentration in the buffer zone inflow was no higher than is typical for humic brooks or lakes in Finland. The low N2O fluxes indicated that forestry operations in the catchment did not result in significant N enrichment of the buffer zone. This study does not support the postulate that peatland buffer zones may become significant sources of N2O.