Effect of proximity to highways on soil chemical properties and grass condition at Mafikeng, South Africa

Abstract

Roads have motor vehicle traffic-sourced ecological effects. This study examined the effect of proximity to roads on soil and grass. Surface soil samples were collected along 60 m transects perpendicular to the four major paved highways of Mafikeng, in two location settings: rural and urban. The pH, colour and cation exchange capacity (CEC) (for all samples), and base saturation (BS), lead (Pb) and manganese (Mn) concentrations (for urban samples only) were determined. Change in normalised difference vegetation index values derived from a satellite image was used to assess effects of roadside proximity on grass vigour. In most transects CEC increased with distance from the road edge. The pH was neutral (7.4 ± 0.14) close to the roads and slightly acidic farther from the roads. High traffic-impacted urban soils had lower CEC (mean = 19.01 cmol(+) kg⁻¹) than rural soils (mean = 20.1 cmol(+) kg⁻¹) (p > 0.05). The concentrations of the heavy metals Pb and Mn were within environmental quality standards. Near roads the grass was less vigorous and Stenotaphrum spp. were dominant, whereas Eragrostis spp. were dominant farther from the roads.