Spatial and Temporal Variability of Soil Respiration Fluxes from Alpine and Subalpine Soils in the East River Watershed, Colorado

Soil respiration of carbon to the atmosphere represents one of the largest fluxes of the terrestrial carbon cycle and is sensitive to changes in temperature, soil moisture, and processes affecting carbon stability. Despite the importance of these sensitivities, few studies have examined the spatial and temporal heterogeneity of soil CO2 fluxes and their controls on intermediate- to large-scale integrated soil fluxes. In this study, we examine spatial variability at scales of 10-5 -101 km2 and temporal variability at scales of hours to months of soil CO2 fluxes through the 2016 growing season in the East River Watershed, CO. We present analyses of (1) temporal variability of CO2 fluxes from four locations with depth-resolved temperature, moisture content, soil gas pCO2, and soil carbon content measurements; (2) spatial variability of CO2 fluxes and surface soil water content across a gridded hillslope with 74 points over an area of 2.5 x 10-3 km2 measured at multiple times throughout the growing season; and (3) variability of CO2 fluxes and surface soil water content from >20 point locations across the 85 km2 catchment targeting a range of vegetation, slope, and aspect characteristics. Comparing soil CO2 fluxes with depth-resolved temperature, moisture, pCO2 and carbon content, we calculate depth-resolved CO2 production rates and their correlations with soil conditions. Gridded hillslope flux measurements reveal strong and consistent variability across separation distances of 1 - 30 m with a slight dependence on slope position, likely representing the controls of lateral flow on soil moisture content. Finally, we analyze correlations of soil CO2 fluxes from point measurements representing broad-scale landscape units with vegetation and geomorphological characteristics. Combining these observations, we examine the implications of our results for interpolating point flux measurements to the catchment scale and for calculating integrated fluxes through the growing season.