Fluxes and production of N2O, CO2 and CH4 in boreal agricultural soil during winter as affected by snow cover

Agricultural soils are important source of atmospheric nitrous oxide (N2O) and a considerable part of annual N2O release occurs during the cold season in the boreal region. According to recent studies N2O can be produced in soils at low temperatures, below 0 ◦C. We studied if removal of the snowcover lowers soil temperatures and whether this would affect flux rates of N2O, carbon dioxide (CO2) and methane (CH4) from an agricultural soil in eastern Finland. Gas flux rates and concentrations in soil were measured from study plots with undisturbed snow cover and from plots with snow removed. This experiment simulates changes in the soil thermal conditions with less snowfall. Plots without snow had even 15 ◦C lower temperature at the depth of 5 cm and they had higher N2O emissions during soil freezing and thawing. However, there were only minor changes in CH4 or CO2 flux rates after removal of snow over the cold season. N2O and CO2 accumulated in the soil during winter and were then released rapidly during thawing in spring. CH4 concentrations in the soil remained lower than the atmospheric levels during winter and subsequently increased to the ambient levels after thawing. Future climate scenarios suggest possible decline in snowfall in northern Europe resulting in lower soil temperatures. This could lead to higher N2O emissions from boreal agricultural soils.