Heterogeneous World Underfoot: Visualizing Soil-Water Interactions in the Critical Zone.

Understanding complex subsurface heterogeneity and their relations to soil-landscape features is essential to predicting flow and transport dynamics across scales. The dearth of effective and compelling visualizations of the complex world underfoot has limited our understanding and quantificaton of subsurface flow and transport. This study employs multiple techniques of visualization and real-time monitoring to reveal the complexity of soil-water interactions in the Critical Zone, including computed tomography at the pore and column scales, ground penetrating radar at the pedon and hillslope scales, eletromanagtic induction and soil moisture mapping at the catchment scale. Through 3- and 4-dimensional investigations using these tools in the forested Shale Hills Catchment, an internal network structure in the subsurface of the catchment is proposed. This subsurface network governs the vertical and lateral preferential flow dynamics in the catchment and a threshold-like hydrologic response under different precipitation inputs, soil types, and antecedent wetness conditions. Based on extensive soil hydrologic monitoring, we are constructing a subsurface flow network model that would capture critical nodes (i.e., important junctions of flow networks that control subsurface flow) and dicpict the first controls of soil hydrology at different scales in this catchment.