Research NoteImpacts of mine dump pollution on plant species diversity, composition and structure of a semiarid savanna in Namibia

Effects of mine dump pollution on semiarid savanna vegetation were investigated in Kombat, Namibia. Vegetation structure, species richness, composition and diversity were compared between polluted and control sites. Concentrations of arsenic, chromium, copper, lead and zinc in soils were significantly higher closer to a 99-year-old mine dump than in a control site and exceeded internationally recommended guidelines by as high as 11 times. Mine dump pollution has significantly reduced woody plant densities, species richness and diversity in the affected area due to disappearance of pollution-sensitive species and preponderance of tolerant ones. Species composition and structure of vegetation close to the mine dump significantly changed, possibly due to negative impacts of heavy metals on recruitment as pollution-sensitive species died off, whereas tolerant species invaded the vacated ecological niches. Ordination analyses confirmed a strong pollution gradient, with measured heavy metals accounting for 57.3% of the observed variation in species data, suggesting that other factors are also important determinants in the area. It is recommended that the mine dump and its surrounds should be rehabilitated and regular monitoring should be carried out to remedy the situation and arrest further pollution of the surrounding environment.Keywords: heavy metals, Kombat, ordination, vegetationAfrican Journal of Range & Forage Science 2011, 28(3): 149–15