Effect of snowpack pattern on cold-season CO2 efflux from soils under temperate continental climate

Abstract

The seasonal snowpack plays an important role in the ecosystem–atmosphere CO2 exchange, especially in temperate continental regions, preventing frost penetration into the soil and thus impacting the CO2 efflux from soils. Due to current climate changes, the snow cover period in many Russian regions has become shorter because of the later onset of snowpack formation and earlier start of snow cover loss. This study focuses mainly on the estimation of cold-season CO2 effluxes from soils at different snow cover depths under the temperate continental climate. An experiment with regulated snow cover was established on grassland and bare soil Haplic Luvisols (in the Moscow region). For each land cover type, the following winter scenarios were applied: (1) reference plot, designated “Ref”, with natural depth of snowpack, (2) no-frost, “NoFr” (simulation of snow addition using artificial heat insulation material), and (3) no-snow, “NoSn” (removal of snowpack). The reduction of snow cover depth accompanied by the frost penetration into the soil was shown to decrease the cold-season CO2 effluxes from soil by 1.7–2.5 times in comparison with unfrozen soil. During the cold season, there were four thaw events, which induced CO2 efflux pulses of varying intensity. The highest peaks of CO2 efflux (up to a 26-fold increase compared to the pre-thawing period) were revealed during the early spring thaw. These pulses in CO2 effluxes during early spring contributed between 43 and 70% to the total cold-season CO2 effluxes from frozen soils (‘Ref” and “NoSn” variants) while the contribution of spring fluxes from unfrozen soils (“NoFr” treatment) was about 22–23%. Grass cover provided both a later winter freezing and delay of spring thawing of soils. Our findings produce evidence that warm and dry winter of 2014–2015 in the temperate continental region is followed by disturbances of the seasonal snowpack, frequent thawing events, prolongation of the period when soils remain frozen that result in the cooling of soils and significant reduction of the cold-season CO2 effluxes from soils.