Rebecca R. Bourgault, University of Vermont, Burlington, VT, Donald S. Ross, Plant and Soil Science, University of Vermont, Burlington, VT, Scott W. Bailey, USDA Forest Service (FS), North Woodstock, NH, Tom Bullen, US Geological Survey, Menlo Park, CA and Kevin J. McGuire, Forest Resources and Environmental Conservation and Virginia Water Resources Research Center, Virginia Tech, Blacksburg, VA
Soils, groundwater, and surface waters of headwater catchments are inter-connected physically and chemically, and their interactions may be studied within the framework of hydropedology. In headwater catchments such as Watershed 3 (WS3) of Hubbard Brook Experimental Forest, soils are thought to be the main source of solutes to streams. Over 100 soil profiles were described and sampled by horizon along transects throughout WS3. The soils were classified into five functional groups called hydropedologic units (HPUs), which were established according to morphological and chemical characteristics relating to groundwater dynamics and water flux direction. Three catenas (with 3-4 soils each) were sampled intensively (every 5 cm of depth) in order to better determine the effects of vertical vs. lateral flow on soil development. Soil samples were analyzed for extractable elements used as hydropedologic tracers. As expected, there were significant differences between HPUs that could be explained by hydropedologic processes. The soils showed typical vertical podzolization on steep, well- to moderately well-drained backslopes (mostly Haplorthods). However, other soils showed possible lateral unsaturated groundwater flow and lateral soil development in areas near bedrock outcrops, benches, and gently sloping riparian zones in moderately well- to somewhat poorly drained conditions (Haplohumods, Humudepts, Epiaquepts, etc.). Observations of morphology and micromorphology were consistent with physical lateral transport of spodic materials. Redox-sensitive elements manganese and cerium have been preferentially transported downslope. These results emphasize the importance of lateral, saturated and unsaturated flow as a soil-forming factor in steep regions with shallow, coarse-textured soils, and the use of soil morphology and chemistry to infer water table regimes and stream solute export. Also, this hydropedologic approach could be applied to other soil mapping efforts in order to better predict soil morphology, classification, and chemistry.
