Landforms, soil development, and shallow water table dynamics: implications for hydrological connectivity at the catchment scale

Hydrological connectivity is regarded as one of the key controls in determining catchment runoff response and flowpaths controlling the export of minerals and nutrients from uplands to streams. We sought to determine the patterns of hydrologic connectivity by characterizing soils and shallow water table development in different landscape positions in a small headwater catchment. Previous investigations in the upland headwater catchments at the Hubbard Brook Experimental Forest characterized soils as well drained Spodosols. However, recent hydrologic monitoring documented transient water table development and wet soil conditions that were persistent during the non-growing season, and occasionally developed during storm events in certain landscape positions during the growing season. Detailed soil sampling revealed a range in spodic expression, including inclusions of Inceptisols with umbric epipedons. Variation in landform along hydrologic pathways, including breaks in slope, slope curvature, and variation in depth to confining layers (bedrock or densipan) explained much of the variability in soil development as well as soil chemical characteristics such as exchangeable acidity and carbon accumulation in mineral horizons. Several topographic indices, particularly distance to stream were statistically significant predictors of pedon morphology and chemistry. Results from this study suggest that the interactions between landform, soil moisture, and soil development patterns can lead to spatial predictions of carbon accumulation, soil chemical characteristics, and soils that become hydrologically connected to runoff producing areas.