Impact Of Mine Pollution On Composition, Diversity And Structure Of Plant And Ground-Dwelling Invertebrate Communities Around Kombat Mine Tailings Dump, Namibia

ABSTRACT

The impact of heavy metal pollution on vegetation and communities of ground-dwelling invertebrates was investigated at Kombat Mine tailings dump in Namibia. Sixteen transect lines were marked around the dump. Plots, 15m x 15m, were marked at 50m intervals along each transect. Top soils in the demarcated plots were sampled and analysed for concentrations of heavy metals and total sulphur. Woody plant species were identified, counted and heights measured. Herbaceous plants were identified and the cover was visually estimated. Pitfall traps were used to sample invertebrates. Soil analysis results indicated that concentrations of copper, lead and total sulphur around the dump exceeded CCME guidelines. There were significant differences in plant species richness (F = 6.1, df = 4, p < 0.01), diversity (F = 5.87, df = 4, p < 0.001), tree density (F = 11.31, df = 4, p = 0.02) and herbacous cover (H = 18.18, df = 4, p < 0.001) along the distance gradient from the dump to the control sites. Shrub density was not significantly different (H = 4.39, df = 4, p = 0.355) along the distance gradient. The abundance of ground-dwelling invertebrates was higher in wet than dry season. Abundance (H = 2.32, df = 4, p = 0.68), richness (H = 8.5, df = 4, p = 0.11) for wet and Abundance (H = 1.41, df = 4, p = 0.24) richness (H = 6.7 df = 4, p = 0.15) dry season of ground-dwelling invertebrate Orders did not significantly differ along the distance gradient. Hierarchical Cluster Analysis on binary plant species data separated vegetation into 4 clusters indicating significant changes in species composition. Indirect gradient analysis showed clear separation of control plots from polluted sites. Direct gradient analysis showed that pollution from

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heavy metals and total sulphur negatively influenced plant species and ground-dwelling invertebrate Orders (wet season) composition accounting for 29.2% and 30.14% of the observed variation in plant species and ground-dwelling Order data respectively. It was concluded that heavy metal pollution had significant impact on the structure and composition of vegetation around the Kombat Mine tailings dump. The impact of heavy metals on ground-dwelling invertebrate communities was inconclusive.

Key words: diversity, heavy metals, invertebrates, Kombat Mine, Namibia, pollution, structure, tailings dump, vegetation.