SOLUTE TRANSPORT IN SEASONAL PERCHED WATER TABLES IN LOESS-DERIVED SOILSCAPES

Hydraulically restrictive fragipans and argllic horizons are a common feature of loessial soils in the Palouse region of northern Idaho, res ulting in perched water development during the winter and early spring , The high relief of the region may result in lateral flow of perched water and solutes. This study was initiated to quantify the rates of s olute movement through perched water at three sites receiving 610, 700 , and 830 mm of annual precipitation, Three transects, perpendicular t o slope contours, consisting of seven, nine, and seven sampling wells, were installed at each site, Five kilograms of KBr tracer were applie d in a trench upslope from the transects. Water samples were drawn biw eekly to test for Br-. Rate of Br- movement and saturated hydraulic co nductivity (K-sat) of soil horizons were used to quantify flow of perc hed water. Results indicate that maximum observed Br- transport decrea sed with annual precipitation and was 86, 50, and 35 cm d(-1) at the 8 30, 700, and 610-mm sites, respectively. Depth profiles for Ksat are s imilar among sites; values range from 63 to 129 cm d-(1) in the Ap hor izons and decrease with depth to 0.10 to 0.21 cm d(-1) in the restrict ive horizons. The E horizons immediately above the argillic-fragipan h orizons have K-sat values from 1.2 to 5.2 cm d(-1) suggesting that muc h of the rapid solute transport via perched water tables occurs in the more permeable horizons overlying the E horizons. Our results demonst rate that perched water flow through these landscapes may enhance agri chemical transport, thereby impacting both nutrient-use efficiency and local water quality.