Lithology can strongly influence preferential flow and soil moisture. We compared soil moisture and preferential flow in two small catchments of contrasting lithology: a shale site (Shale Hills) and a sandstone site (Garner Run). Besides the lithological difference, these two sites also differ in hillslope morphology, soil type, and tree species. Soil moisture probes were installed at 10, 20, and 40 cm for each site (called “Ground HOG”). Each catchment has four Ground HOG sites, which are located at North mid-slope, South ridge top, South mid-slope, and South toe slope. Compared with the Garner Run, the Shale Hills has a steeper South slope. In this study, we first analyzed the frequency of preferential flow events for 8 Ground HOG sites based on soil moisture response time at the three depths, and then calculate the soil water storage for each Ground HOG site based on a depth-weighted method. For both the Shale Hills and the Garner Run, it took around 60 events for PF frequency to reach temporal stability, which is in consistent with our previous studies. The only exception was the Shale Hills North mid-slope, where its PF frequency increased after 50 events and reached temporal stability at around 90 events, which might indicate the inner-structure change at this site. Our preliminary results show significant difference in preferential flow occurrence between the two catchments. For example, at the Shale Hills, the North mid-slope site had a PF frequency of more than 30%, while at the Garner Run, the North mid-slope site had less than 10% PF frequency. We contribute this higher PF frequency at the Shale Hills to its higher clay content, which created more cracks during late summer and early fall. Moreover, at the Shale Hills, lower antecedent water content is more prone to generate PF; while at the Garner Run, PF is more easily generated under wetter condition. This may indicate different mechanisms for these two catchments to generate PF: hydrophobicity vs pre-wetting channel. For soil water storage, the Shale Hills showed an overall higher soil moisture content (around 25%) as compared to the Garner Run (around 18%), which was attributed to different soil types in the two catchments. In addition, our results showed that different tree species also influenced the hydrological processes, such as the drying speed during each summer.
Tang, Q., Guo, L., Eissenstat, D.M., Lin, H. (2017): Comparing preferential flow and soil moisture dynamics in two catchments of contrasting lithology. 2017 American Geophysical Union Fall Meeting, New Orleans, LA, 11-15 Dec .
This Paper/Book acknowledges NSF CZO grant support.