The annual carbon dioxide cycle in a montane soil: Observations, modeling, and implications for weathering.

Profiles of CO₂ concentrations in soil and snow, soil respiration, soil and snow temperatures, and shallow groundwater chemistry were monitored from March 1984 to July 1985 in a montane region near Brighton, Utah. Significant seasonal variations in the concentrations of CO₂ in soil and snow occurred, and two principal rise-decline cycles were observed. During the first cycle the concentration of soil CO₂ at 35 cm rose from 4200 ppmv in July to a maximum of 12,400 ppmv in August and then declined to 4300 ppmv by October. This cycle is attributed to the changing production rate of soil CO₂ during the growing season. During the second cycle the concentration of CO₂ at 35 cm began to rise in November, reached a maximum of 7200 ppmv in early spring, and quickly declined to 3200 ppmv by late spring shortly after the snow cover had melted. This cycle is attributed to deterioration in the exchange of CO₂ between the soil and atmosphere due to a deep snowpack. A model based on Pick's second law of diffusion was developed to account for the temporal and spatial distribution of soil CO₂. The model predicts that soil CO₂ at 35 cm is increased by as much as 15 times due to the deep snowpack. The elevated concentration of soil CO₂, abundance of water, and above-freezing soil temperatures imply that significant soil weathering occurs during the winter in montane regions. [ABSTRACT FROM AUTHOR]