Influence of landscape position and transient water table on soil development and carbon distribution in a steep, headwater catchment

Upland headwater catchments, such as those in the Appalachian Mountain region, are typified by coarse textured soils, flashy hydrologic response, and low baseflow of streams, suggesting well drained soils and minimal groundwater storage. Model formulations of soil genesis, nutrient cycling, critical loads and rainfall/runoff response are typically based on vertical percolation, development of soil horizons parallel to the land surface, mineral weathering inputs limited to the rooting zone and drainage from lumped catchment reservoirs (e.g., the subsoil) as the dominant source of stream flow. However, detailed study of the hydrologic reference catchment at Hubbard Brook Experimental Forest, NH, USA shows striking spatial patterns of soil development that reflect the influence of transient water tables within the solum in nearly all landscape positions. Shallow bedrock and variably low hydraulic conductivity in the subsoil promote lateral flow and development of soil horizons along hillslope flowpaths rather than in vertical profiles. We distinguished several morphologic units based on the presence of diagnostic horizons indicative of differing patterns of podzolization and carbon storage. The distribution of soils appears to be highly dependent on local drainability and frequency and duration of transient saturation within the solum. As such, monitoring of hydropedologic groups and transient water table fluctuations may prove to be a sentinel for the effects of climate change on spatial distribution of soils and retention/release of solutes from upland catchments.