CARBON-DIOXIDE EVOLUTION FROM SNOW-COVERED AGRICULTURAL ECOSYSTEMS INFINLAND

The release of CO2 from the snow surface in winter and the soil surfac e in summer was directly or indirectly measured in three different soi l types (peat, sand and clay) in agricultural ecosystems in Finland. T he closed chamber (CC) method was used for the direct and Fick's diffu sion model (DM) method for the indirect measurements. The winter soil temperatures at 2-cm depth were between 0 and 1 degrees C for each soi l type. The concentration of CO2 within the snowpack increased linearl y with snow depth. The average fluxes of CO2 calculated from the gradi ents 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 C O2 m(-2) h. These results suggest that the snow insulates the soil the rmally, allowing CO2 production to continue at soil temperatures sligh tly above freezing in the winter. Carbon dioxide formed in the soil ca n move across the snowpack up to the atmosphere. The winter/summer rat io of CO2 evolution was estimated to exceed 4%. Therefore, the snow-co vered crop soil served as a source of CO2 in winter, and CO2 evolution constitutes an important part of the annual CO2 budget in snowy regio ns.