In order to increase understanding of parent material controls on biogeochemical processes, we monitored the depth distribution of soil CO2 and O2 concentrations in central Pennsylvania in two watersheds on different lithologies. We deployed gas monitoring instrumentation on two catena transects, one located on sandstone and the other on shale. As expected, with increasing soil depth, O2 concentrations decreased while pCO2 increased. Over the year of monitoring, CO2 concentrations varied between the shale and sandstone locations. When soils were consistently wet (e.g. September and October 2015) pCO2 at 25 cm below the soil surface was 2 to 3 times greater on the sandstone ridgetop and north-facing mid-slope than its shale counter-parts. During the rest of the growing season, CO2 and O2 concentrations varied more by topographical position than with lithology, as the valley floor positions in both catenas had the highest pCO2 for a given depth. Both infrequent manual sampling from many gas access tubes and continuous sampling by a limited number of buried sensors documented these patterns. Because these sites are in close proximity with similar temperature and precipitation, we hypothesize that elevated pCO2 in the surface of sandstone-derived soils (relative to shale) is a result of a thicker organic horizon and differences in the associated heterotrophic respiration. At depth, the higher pCO2 at the sandstone site may be due to a combination of carbon availability and constraints of diffusion. Adjacent forests underlain by shale and sandstone parent materials are prevalent throughout the Appalachian Mountains and if our sites are representative of this region, processes related to soil CO2 and O2, including weathering rates, nutrient cycling, microbial productivity, root growth, and soil respiration may differ markedly in these adjacent forests.
Hill, L.Z., Kaye, J.P., and Brantley, S.L. (2016): Soil CO2 and O2 concentrations in shale and sandstone catchments of central Pennsylania. 2016 Fall Meeting, American Geophysical Union, San Francisco, CA, 12-16 Dec..
This Paper/Book acknowledges NSF CZO grant support.