Mapping of Hydropedologic Spatial Patterns in a Steep Headwater Catchment

Abstract

A hydropedologic approach can be used to describe soil units affected by distinct hydrologic regimes. We used field observations of soil morphology and geospatial information technology to map the distribution of five hydropedologic soil units across a 42-ha forested headwater catchment. Soils were described and characterized at 172 locations within Watershed 3, the hydrologic reference catchment for the Hubbard Brook Experimental Forest, New Hampshire. Soil profiles were grouped by presence and thickness of genetic horizons. Topographic and bedrock metrics were used in a logistic regression model to estimate the probability of soil group occurrence. Each soil group occurred under specific settings that influence subsurface hydrologic conditions. The most important metrics for predicting soil groups were Euclidean distance from bedrock outcrop, topographic wetness index, bedrock-weighted upslope accumulated area, and topographic position index. Catchment-scale maps of hydropedologic units highlight regions dominated by lateral eluviation or lateral illuviation and show that only about half the catchment is dominated by podzolization processes occurring under vertical percolation at the pedon scale. A water table map shows the importance of near-stream zones, typically viewed as variable source areas, as well as more distal bedrock-controlled zones to runoff generation. Although the catchment is steep and underlain by soils developed in coarse-textured parent material, patterns of groundwater incursion into the solum indicate that well-drained soils are restricted to deeper soils away from shallow bedrock and the intermittent stream network. Hydropedologic units can be a valuable tool for informing watershed management, soil C accounting, and understanding biogeochemical processes and runoff generation.