Soil Profile CO2 concentrations in forested and clear cut sites in Nova Scotia, Canada

Subsurface soil CO2 concentration is an important component of the terrestrial C budget and site specific information on the spatial and temporal variability and how it responds to forest management is needed for accurately estimating ecosystem C budgets. The objectives of this study were to examine the within site spatial and seasonal variability, and differences between sites of subsurface CO2 concentrations as affected by microtopography, clear cut harvesting, and soil texture. To address these objectives, we used two paired forested and clear cut sites of contrasting soil texture in Nova Scotia, Canada. The soil texture at the Lakevale pair (LF = intact forest and LCC = clear cut) was sandy while that of Pomquet (PF: intact forest and PCC = clear cut) was clayey. Two and half-years after clear cut harvesting, data were collected from each site on an approximately monthly time interval for 1 year from four mineral soil depths (0, 5, 20 and 35 cm) and 10 microsites separated by approximately 10 m and representing three local topographic features (level, trough and hump). We also monitored soil temperature and moisture with depth at a representative location at each site. Soil CO2 showed high within site variability and ranged between 346 and 28,086 ppmv (median = 2835) for LF, 319–29,135 (median = 2802) for LCC, 364–29,016 (median = 2345) for PF, and 407–81,053 (median = 5690) for PCC. Differences due to microtopographic positions were not statistically significant (p > 0.05). Median CO2 concentration and its variability generally increased with depth. Seasonally aggregated data indicated a distinct pattern with median CO2 concentrations as high as 8646 ppmv (95% confidence interval = 6937–12,142) during summer at PCC and as low as 1570 ppmv (95% confidence interval = 1290–1920) at LCC during winter. Despite the high within site variability, PCC showed significantly higher median CO2 concentration than PF. No significant difference in subsurface CO2 concentration was found between LF and LCC. Subsurface CO2 concentration showed significant quadratic correlation (R2 = 0.32–0.85, p < 0.05) with soil temperature and volumetric water content only for the Lakevale sites, suggesting the presence of strong soil texture control on subsurface CO2 concentration dynamics at these sites.