Carbon dioxide evolution from snow-covered agricultural ecosystems in Finland

The release of CO₂ from the snow surface in winter and the soil surface in summer was directly or indirectly measured in three different soil types (peat, sand and clay) in agricultural ecosystems in Finland. The closed chamber (CC) method was used for the direct and Pick's diffusion model (DM) method for the indirect measurements. The winter soil temperatures at 2-cm depth were between O and 1°C for each soil type. The concentration of CO₂ within the snowpack increased linearly with snow depth. The average fluxes of CO₂ calculated from the gradients of CO₂ concentration in the snow using the DM method ranged from 10 to 27 mg CO₂ m^-2 h^-1, and with the CC method from 18 to 27 mg CO₂ m^-2 h^-1. These results suggest that the snow insulates the soil thermally, allowing CO₂ production to continue at soil temperatures slightly above freezing in the winter. Carbon dioxide formed in the soil can move across the snowpack up to the atmosphere. The winter/summer ratio of CO₂ evolution was estimated to exceed 4%. Therefore, the snow-covered crop soil served as a source of CO₂ in winter, and CO₂ evolution constitutes an important part of the annual CO₂ budget in snowy regions.