Perched water tables on Argixeroll and Fragixeralf hillslopes

Seasonally perched water tables (PWTs) are common in loess-derived Argixerolls and Fragixeralfs of the Palouse region of northern Idaho and eastern Washington, However, little is known about the short-term PWT dynamics in these rolling to hilly landscapes and how they are influenced by a regional climatic gradient. In this study, PWTs on an Argixeroll hillslope receiving 700 mm of mean annual precipitation (MAP) and a Fragixeralf hillslope receiving 830 mm of MAP were monitored hourly for four seasons. Results demonstrate that timing of PWT formation may vary considerably from year to year, and may occur up to 3 wk earlier in Fragixeralfs than in Argixerolls, Once formed, the PWTs respond rapidly to precipitation and snowmelt in both soils, with PWT levels increasing as much as 60 cm within a period of < 24 h, Water table levels are at or near the soil surface numerous times during the season following periods of rainfall or snowmelt, Perched water table dynamics are remarkably consistent across the region, with similar responses observed in hillslopes located 28 km apart. Relatively dense, light-colored E horizons overlying the restrictive horizons remain continuously saturated for up to 6 to 7 mo yr(-1) and develop redox potentials sufficiently low for Fe reduction to occur. Results suggest that seasonal PWTs drive the processes of ferrolysis and hydroconsolidation, and these processes are responsible for many of the E horizon properties common to Argixerolls and Fragixeralfs of the region.