Quantifying soil gas dynamics is needed for global C cycle models, projecting feedbacks between climate change and terrestrial ecosystem C balance, and assessing bedrock weathering through enhanced acidity from CO2 dissolution into porewaters. We seek to link patterns in soil CO2 fluxes with dissolved inorganic C (DIC) in porewaters, which will allow modelling of CO2 loss from soils to the atmosphere and through the advective outflux of DIC-containing porewaters from watersheds. Soil CO2 fluxes were measured at the land surface and calculated at depth using Fick’s Law, pCO2, and soil properties for a first-order catchment at the Susquehanna Shale Hills Critical Zone Observatory . We measured soil CO2 along a planar slope and swale depression, with discrete
sampling depths at the ridge, mid-slope, and valley. We compared CO2 flux data with DIC for soil porewaters and groundwater . Surface CO2 flux positively correlates with soil temperature and moisture up to 0.25 m3 m-3; above this value it is negatively correlated with soil moisture. On average, surface CO2 flux is higher for the wetter swale depression (4.67±2.96 μmol m -2 s-1) than the drier planar slope (3.67±2.48 μmol m-2 s-1). However, there is high spatial variability along the two transects that does not correlate with hillslope position or soil depth, but is likely the result of heterogeneous leaf litter distribution (R2 = 0.69). At depth, CO2 fluxes to the atmosphere decrease rapidly (to ~1 μmol m2 s-1 at 10 cm and to nearly zero below 30 cm) and are positively correlated with porosity and negatively correlated with soil moisture. Under drier conditions and at >50 cm depth, we observe small CO2 fluxes towards the groundwater. This downward flux is confirmed by observations of groundwater δ 13CDIC that indicate mixing between DIC from soil CO2 and ankerite dissolution in the parent shale .
 Hasenmueller et al. (2015) Appl. Geochem. 63, 58-69.
 Jin et al. (2014) Geochim. Cosmochim. Acta 142, 260-280.
Elizabeth A. Hasenmueller*, Pamela L. Sullivan, Julie N. Weitzman, Susan L. Brantley, and Jason P. Kaye (2018): Soil CO2 Fluxes Through a Temperate Watershed. Abstract 11g:338 presented at 2018 Goldschmidt Meeting, Boston, MA 12-17 August.
This Paper/Book acknowledges NSF CZO grant support.