Solute Transport in Seasonal Perched Water Tables in Loess‐Derived Soilscapes

Abstract

Hydraulically restrictive fragipans and argillic horizons are a common feature of loessial soils in the Palouse region of northern Idaho, resulting 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 solute movement through perched water at three sites receiving 610, 700, and 830 mm of annual precipitation. Three transects, perpendicular to slope contours, consisting of seven, nine, and seven sampling wells, were installed at each site. Five kilograms of KBr tracer were applied in a trench upslope from the transects. Water samples were drawn biweekly to test for Br‐. Rate of Br‐ movement and saturated hydraulic conductivity (Ksat) of soil horizons were used to quantify flow of perched water. Results indicate that maximum observed Br‐ transport decreased with annual precipitation and was 86, 50, and 35 cm d‐1 at the 830, 700, and 610‐mm sites, respectively. Depth profiles for Ksat are similar among sites; values range from 63 to 129 cm d‐1 in the Ap horizons and decrease with depth to 0.10 to 0.21 cm d‐1 in the restrictive horizons. The E horizons immediately above the argillic‐fragipan horizons have Ksat values from 1.2 to 5.2 cm d‐1 suggesting that much of the rapid solute transport via perched water tables occurs in the more permeable horizons overlying the E horizons. Our results demonstrate that perched water flow through these landscapes may enhance agrichemical transport, thereby impacting both nutrient‐use efficiency and local water quality.

Simulating field-scale variability and precision management with a 3D hydrologic cropping systems model

“…The eastern Palouse is dominated by hydraulically restrictive layers (argillic or fragipan horizons) that limit the depth of root penetration and generate perched water tables and sub-surface lateral flow (Brooks et al 2012). Across the study site, hydraulically restrictive horizons are found between 0.3 and 1.5 m below the surface, as determined using a 1 650 kg m -3 bulk density threshold to establish presence of a restrictive horizon (Reuter et al 1998). Palouse fields have high spatial variability with short and steep (45-55% slope) northeast facing slopes and longer, more gradual southwest facing slopes (Brooks et al 2012).…”

“…Step 1) and a 1 650 kg m -3 bulk density threshold to establish presence of a restrictive horizon (Reuter et al 1998). 3.…”

“…Initial and maximum canopy cover, green and total canopy cover at maturity, thermal time at emergence, thermal time at the end of canopy growth, thermal time at the beginning of canopy senescence and thermal time at physiological maturity were adjusted such that in-season simulated potential green area index (GAI) followed the same pattern as maximum LAI observed on the field site. Rooting depth was limited to the upper boundary of the hydraulically restrictive soil horizon (Reuter et al 1998) and root density and distribution values were based on wheat physiology experimentation in representative soils and similar tillage management to the field site (Martinez et al 2008;Nosalewicz and Lipiec 2014).…”

Distributed and integrated response of a geographic information system‐based hydrologic model in the eastern Palouse region, Idaho

“…These soils are classified as Fragic Luvisols using the World Reference Base for Soil Resources. Typical soil horizonation consists of an Ap, Bw, E, and a Btxb (fragipan) that occurs at an average depth of 0Ð86 m. These fragipans have low K s (0Ð1 to 1 mm day 1 ), high bulk density (¾1650 kg m 3 ), and relatively high clay content (typically 6 to 8% larger than the overlying soil horizons) (Reuter et al, 1998;McDaniel et al, 2001). Seasonal perched water tables develop above the fragipan from approximately November through to May (McDaniel and Falen, 1994;McDaniel et al, 2001).…”

An assessment of vegetation characteristics and hydrologic flow pathways on the effectiveness of vegetated buffer strips for phosphorus reduction in an agricultural watershed

“…At these sections, dye stained the soils horizontally indicating there was lateral flow occurring. Soils closer to the surface are typically higher in soil P concentrations, so lateral movement along the more impenetrable layer could lead to the transport of higher concentrations of nutrients than vertical infiltration deeper in the soil profile (Reuter, McDaniel, Hammel, & Falen, 1998;Walter et al, 2000).…”