The dynamics of soil carbon dioxide (CO2) efflux under snowpack are poorly understood despite implications to the fields of soil biology, ecosystem ecology, and atmospheric chemistry. Recent research has shown that soil CO2 efflux may continue under snow during the winter at low rates. Near Flagstaff, in northern Arizona, USA, approximately half the annual precipitation falls as snow. These storms typically produce heavy snowfall accumulations yet often melt rapidly. The purpose of this study was to observe the dynamics of soil CO2 efflux during snowmelt. In March, 2006, we measured CO2 efflux in a grassland created by fire ten years earlier in northern Arizona, USA, using two separate continuous measurements: 1) buried steady state probes that measured a soil CO2 diffusion gradient profile and 2) an eddy covariance tower positioned 2 m above the canopy which measured net ecosystem exchange of CO2.
Results/Conclusions
Using the soil CO2 diffusion gradient profile, we observed that soil CO2 efflux occurred under snow at consistently low levels with less diel variation than when no snow was on the ground; soil temperatures were also less temporally variable under snow. However, the eddy covariance tower measured clear, distinct spikes of CO2 released to the atmosphere during periods of snowmelt. Periods of snowmelt were indicated by warmer air temperature and lower albedo measured by the eddy covariance tower. The discrepancy between these two methods suggests that the air-filled pore space in the snowpack contained soil-respired CO2. As this snow melted, the CO2 in the snowpack was released to the atmosphere and measured by the eddy covariance instruments. The storage of CO2 in snowpack and the subsequent emission during warming events has implications for our understanding of the timing and magnitude of terrestrial CO2 emissions.
