Natural revegetation of hydrocarbon-contaminated soil in semi-arid grasslands

Abstract

One way to identify hydrocarbon-tolerant plant species for reclamation is to sample vegetation at contaminated sites allowed to recover naturally. We compared vegetation and soils of 14 hydrocarbon-contaminated plots in southern Saskatchewan to those of nearby uncontaminated plots to determine the impact on plant communities and soil properties. Contaminated plots had less vegetation and litter cover than uncontaminated plots, and significantly higher soil carbon to nitrogen ratios, pH, and hydrocarbon concentration, and lower nitrogen and phosphorus. Although species richness was not significantly different, Shannon's diversity was lower on contaminated plots. Mean compositional similarity of the plots, measured using Jaccard's index, was only 31%, and cover similarity, measured using Spatz's index, was only 22%. Vegetation composition differences occurred because mycorrhizal, woody and vegetatively reproducing species, and species using birds or unassisted means for seed dispersal were significantly less common on contaminated than uncontaminated plots. Self-pollinated species were significantly more common on contaminated plots. The most abundant species on contaminated soils were the annual forb Kochia scoparia and the native perennial grasses Hordeum jubatum, Distichlis stricta, Agropyron smithii, Agropyron trachycaulum, and Poa canbyi. This research shows that some plant species and functional groups are tolerant of the altered soil conditions at hydrocarbon-contaminated sites.Key words: functional groups, oil spills, phytoremediation, reclamation, succession, vegetation recovery.