Soil structural interfaces in some Texas Vertisols and their impact on solute transport

Abstract

Structural surfaces and slickensides have been reported to be important features impacting sorption–desorption of chemicals and bypass flow of pollutants to shallow groundwater aquifers. This study provides visible, microscopic and submicroscopic characteristics of slickenside features in two Texas Vertisols of different geomorphological age. Transport of visible anionic dye and CaBr is studied as related to soil structural surfaces, root channels and slickenside planes. Macromorphic observations were coupled with thin section microscopy, scanning electron microscopy and electron microprobe analyses. Slickenside surfaces differed from subjacent micromass of the ped interiors by stronger preferred orientation of clay particles and reduction in macropores with corresponding increase in micropores. Such characteristics could make slickensides act as semi-permeable barriers to solute transport, but this phenomenon could not be confirmed from CaBr studies herein. The majority of the solute bypass flow in both soils was conducted through root channels and ped interfaces. Slickenside surfaces in these Vertisols conducted less than 1% of the flow. It was observed primarily when the dye solution was delivered to the surface of the slickenside via the adjacent root channel. In spite of the preferential orientation of clay particles along slickenside planes, the penetration of Br into the aggregate interior was not retarded like the larger organic anion dye. These results may reflect specific moisture conditions, which should be considered in future works.