BROMIDE MOVEMENT AT SELECTED SITES IN A DISSECTED PIEDMONT LANDSCAPE

Soil hydraulic properties vary across landscape positions due to changes in soil profile characteristics. Water and solute transport in soils are intimately related to soil property and water balance relationships. The objectives of this study were to identify the interdependency of solute transport on hydrologic, pedologic, and geomorphic properties of a dissected Piedmont landscape and to determine soil features conducive to lateral water movement within the soil profile. Crystalline KBr was applied at a rate of 1 kg/m2 in 15 m long by 15 cm deep trenches on 11 Aug. 1987 to one linear slope (LS1) and two headslope (HS1 and HS2) positions in a clayey, kaolinitic, thermic Typic Kanhapludult soil under pasture in the Piedmont of North Carolina. Soil cores were taken on 8 Mar. 1988, 20 July 1988, and 3 Nov. 1988 in a grid of sample positions along the trench (PAT) and downslope from the trench (DFT). The highest Br levels on 8 March were found at LS1, followed by HS2, in the B horizons at the 0.25 m DFT. Solute concentrations declined with DFT and time at every site. Differences in Br- distribution with PAT indicated that preferential movement occurred at LS1, but only to a minor extent at HS1 and HS2. The centers of mass of the Br- profiles at LS1 and HS2 were found in the upper B horizons. Bromide moved deeper at HS1, where the soil profile was formed entirely in hillslope alluvium and had the lowest clay and dithionite-extractable iron (Fe(d)) contents throughout the solum. The alluvial-residual parent material discontinuity between the Bt1 and Bt2 horizon of HS2 contributed to greater lateral Br-transport compared with site LS1, where bulk density and macro-porosity changed minimally and/or gradually with depth. Water and Br- transport was dominantly vertical through the soil profile at LS1.