To investigate the role of climate in driving critical zone evolution in shale landscapes, a transect of sites with varying mean annual temperature and precipitation was established in the northern hemisphere as part of the Susquehanna Shale Hills Critical Zone Observatory. The transect includes Appalachian Mountain sites in New York, Pennsylvania, Virginia, Tennessee and Alabama with end members in Wales and Puerto Rico. Here we present our current understanding of critical zone evolution at these sites and our ongoing work to elucidate how temperature and precipitation influence the style and rate of shale weathering, erosion and soil development. Previous work focused on geochemical and mineralogical transformations across the transect reported enhanced weathering and soil development with increasingly warm and wet climates. Plagioclase dissolution may be the reaction that begins the transformation of shale bedrock to weathered regolith, but the more abundant chlorite in the shale parent material more likely controls regolith thickness in these profiles. In contrast, rare earth element release rates are insensitive to climate and instead depend strongly on parent material composition. Ongoing work across the Appalachian transect sites includes quantifying present-day erosion rates using sediment traps and characterizing root density and microbial community composition with depth. Although long-term erosion rates derived from meteoric 10Be concentrations are similar within error across the transect (~40 m Ma-1), present-day erosion rates measured with sediment traps appear to be higher at southern sites compared to northern sites. Root density also appears to differ across the transect, with greater fine root density in Pennsylvania compared to other sites. Despite differences in climate, microbial community composition across four sites in the Appalachian Mountains are virtually indistinguishable from each other; microbial diversity decreases with depth at each site as carbon sources diminish. Results from this ongoing work will help us understand how shale landscapes evolve and respond to ongoing climate change.
Dere, A.L.D., Santini, T., Parcher, S., Nyangari, S., Warren, K. (2017): Critical Zone Evolution Across a Shale Climosequence. 2017 American Geophysical Union Fall Meeting, New Orleans, LA, 11-15 Dec .
This Paper/Book acknowledges NSF CZO grant support.