McDowell, N. G., Marshall, J. D., Hooker, T. D., Musselman, R. (2000/06/01) Estimating CO2 Flux From Snowpacks At Three Sites In The Rocky Mountains,
Tree Physiology, 20(11), 745-753. https://doi.org/10.1093/treephys/20.11.745
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Soil surface CO2 flux (Fs) is the dominant respiratory flux in many temperate forest ecosystems. Snowpacks increase this dominance by insulating the soil against the low temperature to which aboveground components are exposed. However, measurement of Fs in winter may be impeded by snow cover. Likewise, developing annual Fs models is complicated by seasonal variation in root and microbial metabolism. We compared three methods of measuring sub-snow Fs: (1) dynamic chamber measurements at the upper snowpack surface (Fsnow), (2) dynamic chamber measurements at the soil surface via snowpits (Fsoil), and (3) static estimates based on measured concentrations of carbon dioxide ([CO2]) and conductance properties of the snowpack (Fdiffusional). Methods were compared at a mid-elevation forest in northeastern Washington, a mid-elevation forest in northern Idaho, and a high-elevation forest and neighboring meadow in Wyoming. The methods that minimized snowpack disturbance, Fdiffusional and Fsnow, yielded similar estimates of Fs. In contrast, Fsoil yielded rates two to three times higher than Fsnow at the forested sites, and seven times higher at the subalpine meadow. The ratio Fsoil/Fsnow increased with increasing snow depth when compared across all sites. Snow removal appears to induce elevated soil flux as a result of lateral CO2 diffusion into the pit. We chose Fsnow as our preferred method and used it to estimate annual CO2 fluxes. The snowpack was present for 36% of the year at this site, during which time 132 g C m−2, or 17% of the annual flux, occurred. We conclude that snowpack CO2 flux is quantitatively important in annual carbon budgets for these forests and that the static and dynamic methods yield similar and reasonable estimates of the flux, as long as snowpack disturbance is minimized.