Soil chemistry and shale weathering on a hillslope influenced by convergent hydrologic flow regime at the Susquehanna/Shale Hills Critical Zone Observatory

Soil chemistry data (major and REEs) are presented from a swale transect for comparison to similar measurements on a planar transect published previously for the Susquehanna/Shale Hills Critical Zone Observatory. Similar reaction fronts are observed: plagioclase dissolution is indicated by Na and Ca depletion and a negative Eu anomaly; clay dissolution followed by particle loss is accompanied by depletion of Mg, K, Fe, Al and Si. However, in contrast to the planar transect, soils along the swale transect, especially in the topographically depressed site, do not show smooth elemental profiles. This documents both residuum soils and accumulation of colluvium sediments. The soils in the swale transect are thicker and on average wetter than those along the planar transect; however, the Ce anomaly observed in the swale soils is consistent with a generally oxic environment. Thus, preferential flowpaths are an important mechanism for water transport, preventing swale soils from water saturation.

► Soils in a swale are controlled by weathering and colluvium sediment transport.
► Plagioclase and clay dissolution dictates elemental profiles at Shale Hills soils.
► Swales at Shale Hills are wetter but oxic, evidenced by the positive Ce∗ anomaly.