LATERAL AND VERTICAL BROMIDE ION-TRANSPORT IN A PIEDMONT LANDSCAPE

Variation in soil physical properties and soil water transport can affect solute transport at different positions within a landscape. Our objective was to evaluate the magnitude of lateral and vertical transport of Br- under natural rainfall conditions as a function of landscape position. Potassium bromide was surface applied (300 kg Br-/ha) on three transects of Georgeville soil (clayey, kaolinitic, thermic Typic Hapludults) in the Piedmont of North Carolina. Each transect included a footslope, linear slope, and interfluve landscape position. The KBr was applied on alternate plots (5 by 2.7 m) on two transects and on contiguous plots on the third transect. Soil cores as deep as 3 m were collected after 140, 560, and 1460 mm of rainfall. Extent of lateral Br- transport was determined using cores from plots that did not receive surface application of KBr. After 140 mm of rainfall, the maximum Br- concentration remained in the upper 30 cm and some measurable lateral Br- transport occurred at all landscape positions. After 560 mm of rainfall, the maximum Br- concentration was above 60 cm, but some was detected at 150 cm on the footslope and interfluve positions. Lateral transport of Br- at the footslope and linear slope positions was 150 cm, but maximum concentrations occurred 10 to 45 cm downslope. After 1460 mm of rainfall, most Br- disappeared from the footslope. Downslope lateral transport of Br- was 225 cm at all landscape positions. Both vertical and lateral Br- transport were greatest at the footslope. The variability in Br- transport is related to soil profile characteristics and hydrology at different landscape positions.