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Hydropedologic approaches utilize a strategy of ''map first, then design'' and ''direction first, then velocity'' in enhancing the understanding of complex landscape processes. This is illustrated in this study by examples dealing with (i) the mapping of soils and landforms in monitoring and interpreting soil moisture dynamics and (ii) the identification of flow pathways in determining landscape water fluxes.Year-round monitoring at 77 sites in the Shale Hills Catchment in central Pennsylvania revealed a temporal stability of soil moisture spatial pattern as governed by soil types and landforms, and suggested the significance of subsurface preferential flow in rapid channeling of precipitation to stream discharge. The five soil series identified in the catchment had the following decreasing trend of moisture storage within the upper 1.1-m solum: Ernest . Blairton $ Rushtown $ Berks . Weikert. The four landform units showed a decreasing trend of soil moisture storage: Valley . Swale . Hillslope . Hilltop. The 77 monitoring sites exhibited considerable ranking stability throughout the monitoring year at multiple depths, with the subsurface's moisture ranking stability being slightly stronger than that at the surface. A slope-intercept analysis of linear regression further described the four conditions of temporal stability as related to soil moisture and hydrologic dynamics. Because of more extensively distributed deeper soils and hydrologically active swales, plus favorable subsurface lateral flow pathways and slightly higher cumulative rainfall, the south-facing slope in this V-shaped catchment was hydrologically more active than the north-facing slope in terms of draining more water at a faster rate to the stream. Approximately two-thirds of the soil horizons measured in the catchment had lateral saturated hydraulic conductivity (K sat ) values 1.5 to 142.5 higher than vertical values. Because of a moderate slope (up to 25-48%), horizontally dipping shale bedrock (11.5-17.1°), and shallow tree rooting systems (branching laterally), subsurface lateral flow was prominent in this humid forested catchment.

Background and Scope Because of the crucial role coarse roots (>2 mm diameter) play in plant functions and terrestrial ecosystems, detecting and quantifying the size, architecture, and biomass of coarse roots are important. Traditional excavation methods are labor intensive and destructive, with limited quantification and repeatability of measurements over time. As a nondestructive geophysical tool for delineating buried features in shallow subsurface, ground penetrating radar (GPR) has been applied for coarse root detection since 1999. This article reviews the state-ofknowledge of coarse root detection and quantification using GPR, and discusses its potentials, constraints, possible solutions, and future outlooks. Some useful suggestions are provided that can guide future studies in this field. Conclusions The feasibility and accuracy of coarse root investigation by GPR have been tested in various site conditions (mostly in controlled conditions or within plantations) and for different plant species (mostly tree root systems). Thus far, single coarse root identification and coarse root system mapping have been conducted using GPR, including roots under pavements in urban environment. Coarse root diameter and biomass have been estimated from indexes extracted from root GPR radargrams. Coarse root development can be observed by repeated GPR scanning over time. Successful GPR-based coarse root investigation is site specific, and only under suitable conditions can reliable measurements be accomplished. The best quality of root detection by GPR is achieved in well-drained and electrically-resistive soils (such as sands) under dry conditions. Numerous factors such as local soil conditions, root electromagnetic properties, and GPR antenna frequency can impact the reliability and accuracy of GPR detection and quantification of coarse roots. As GPR design, data processing software, field data collection protocols, and root parameters estimation methods are continuously improved, this noninvasive technique could offer greater potential to study coarse roots.

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Summary Characterization of preferential flow at multiple spatial and temporal scales is fundamental to the understanding of complex subsurface heterogeneity and catchment hydrology. Evidence of subsurface preferential flow and the conditions under which it occurs were investigated in the Shale Hills catchment, a humid forested region in central Pennsylvania, USA. Seven monitoring sites, plus five replicates, were established along a concave hillslope, a convex hillslope and a valley floor to monitor in situ the hydrology in various soil horizons and their interfaces at half‐minute intervals. Using the indicator of a lower horizon that responded to a rainstorm earlier than an upper horizon within the same soil profile, we investigated the subsurface preferential flow processes and their dynamics in each of the five soil series mapped in the catchment. Threshold behaviour, hydrophobicity impact, influence of soil thickness and topography were observed in the spatial and temporal variation of the subsurface preferential flow, which was initiated more readily under the conditions of more intense rain, drier initial soil, shallower soil, and steeper slope. Whereas preferential flow seemed common in this catchment, its frequency during the 15 storm events from 23 September 2006 to 1 January 2007 ranged from 0 to 73.3% for the 68 soil horizons monitored at the 12 stations, with an overall average frequency of 7.5% (i.e. ∼5 horizons per storm event). This preferential flow was more frequent during the drier period than that during the wetter one. Variation was observed within the same soil series, even for those profiles adjacent to one another. This was due to the differences in hillslope position, slope gradient and orientation, the underlying bedrock fracture and orientation, or some combinations. Whereas different soil series help differentiate the processes and dynamics involved in the subsurface preferential flow, a combined consideration of soil types and landscape features is important to ensure proper use of the soil data for hydrological applications.