Hydropedology of the Palouse Region: Implications for Erosion, Water Quality, and Groundwater Recharge.

The loess-derived soils and landscapes of the Palouse region of the Pacific Northwest USA provide a unique setting in which to study relationships between soil morphology and near-surface hydrologic processes in seasonally dry landscapes. Spatial variability of soils occurs at a regional scale in response to mean annual precipitation and temperature gradients. Calcium carbonate-containing Mollisols dominate the warmer, drier areas while forested Alfisols dominate the cooler, moister portions of the Palouse. In addition, steep, hilly topography results in considerable spatial variation in microclimate and effective precipitation at the hillslope scale. Fragipans and dense argillic horizons associated with regional paleosols are especially common in the moister areas of the Palouse, and result in formation of extensive seasonal perched water tables and rapid subsurface lateral flow during the wetter winter and spring months. Downward percolation of water through uplands is minimal, thereby minimizing aquifer recharge in these areas. Perched water table dynamics also drive variable source area hydrology. Spatial variability in soil depth and convergence of this lateral flow predominantly drives the generation of saturation-excess runoff. Excessive erosion has occurred over the past century as a result of variable source area hydrology and tillage practices. Development of a conceptual understanding of Palouse region hydropedology has helped inform effective solutions to regional erosion, water quality, and groundwater recharge issues.