Winter greenhouse gas emissions ( CO 2 , CH 4 and N 2 O ) from a sub-alpine grassland

Abstract

Abstract. Carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) fluxes were measured during the winter 2010/2011 at a~sub-alpine managed grassland in Switzerland using concentration gradients within the snowpack (CO2, CH4, N2O) and the eddy covariance method (CO2). Measured snow densities were used to calculate the respective greenhouse gas (GHG) fluxes. Mean winter fluxes based on the gradient method were 0.74 ± 0.53 μmol m−2 s−1 for CO2, −0.14 ± 0.09 nmol m−2 s−1 for CH4 and 0.23 ± 0.23 nmol m−2 s−1 for N2O, respectively. While CO2 and CH4 fluxes decreased with progressing winter season N2O fluxes did not follow a~seasonal pattern. Key variables driving the fluxes of CO2 and CH4 were soil surface temperatures and snow-water equivalent. N2O fluxes were only poorly explained by any of the measured factors in the soil and snow. Spatial variability across the valley floor was smallest for CO2 and largest for N2O. During the winter season 2010/2011 (November–April) greenhouse gas fluxes accumulated to 631–670 g CO2 m−2, −0.04 g CH4 m−2 and 0.13 g N2O m−2. Total greenhouse gas emissions from the grassland were between 669–709 g CO2 eq. m−2, with N2O contributing 5% to the overall budget and CH4 reducing the budget by less than 1%. In comparison with the CO2 fluxes measured by eddy covariance, the gradient technique underestimated the effluxes during the main winter period by 40% but yielded similar fluxes on a seasonal basis. Cumulative budgets of CO2 were smaller than emission reported for other sub-alpine meadows in the Swiss Alps and the Rocky Mountains. It remains unclear how GHG emissions are altered by changes in climate and according snow conditions.