Henry Lin, Crop and Soil Sciences, The Pennsylvania State University, University Park, PA 16802, Xiaobo Zhou, Pennsylvania State Univ., The Pennsylvinia State University, 116 ASI Building, University Park, PA 16802, and Jun Zhang, Crop and Soil Sciences, Penn State University, 116 ASI Building, University Park, PA 16802.
Understanding complex subsurface heterogeneity and their relations to soil moisture spatial-temporal patterns and preferential flow dynamics are fundamental to catchment hydrology. Despite significant progress made in the past decades, our ability to predict preferential flow patterns, thresholds, and pathways in the subsurface across space and time remains limited. It appears that an internal network structure exists in the subsurface of many hillslopes, which governs vertical and lateral preferential flow dynamics and a threshold-like hydrologic response under different precipitation inputs, soil types, and antecedent wetness conditions. We investigated soil moisture spatial-temporal patterns, heterogeneity of soil moisture response to varying rainfalls, triggering of sharp increase in soil moisture content, subsurface network-like behaviors, and their relationships to varying precipitation-soil-landform-bedrock conditions at the Shale Hills, a humid forested catchment in central Pennsylvania. We developed an integrated framework to understand the complex landscape-soil-hydrology relationships across scales, and use the iterative cycle of “mapping, monitoring, and modeling” for understanding catchment hydrology. An integrated approach of soil-landscape mapping, geophysics, hydropedology, hydrometry, and real-time monitoring of soil moisture, precipitation, and stream discharge was used to investigate soil moisture dynamics from the surface down to the bedrock at the catchment, as well as subsurface flow networks and their critical nodes (i.e., important junctions of flow networks in the subsurface that control the threshold behavior of subsurface stormflow). Based on our extensive soil hydrologic monitoring data, different soil hydrologic response groups that show contrasting wetting-drying patterns in response to rainfall events are proposed, which help understand the first-order controls of subsurface preferential flow at the pedon-, hillslope-, and catchment scales. Threshold behavior of soil moisture has been observed in many situations at this catchment. This study demonstrates the benefits of integrating pedological and hydrological expertise within the framework of hydropedology to enhance the monitoring and modeling of subsurface preferential flow patterns and its connection to soil-landscape conditions.
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