Impact of the Tsumeb smelter waste on plant species diversity and structure in Tsumeb, north-central Namibia
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Date
2007
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Abstract
The objective of this study was to determine the impact of the smelter waste on plant species diversity and structure in the Tsumeb area. The most important sources of contamination are solid and gaseous emissions from the Tsumeb Smelter, airborne particles from the Tsumeb tailings pond and airborne particles from slag mill waste. Six sites: Inside Smelter Site, Outside Smelter Site, Abattoir Hill Site, Transnamib Site, Nomtsoub Site and Airport Site were selected and ten 10 m x 10 m plots were randomly demarcated at each site for soil and plant sampling. All 10 m x 10 m plots were used for sampling trees, nested within them were 5 m x 5 m and 2 m x 2 m plots which were used for sampling shrubs and grasses respectively. Top soils were sampled and analysed for concentration of arsenic, cadmium and lead. All trees (basal circumference 15 cm) as well as selected trees species, Combretum apiculatum and Terminalia prunioides were identified, counted and their heights as well as basal circumferences were measured. All shrubs, saplings and seedlings as well as a selected shrub, Dichrostachys cinerea, were identified, counted and their heights were measured. Grasses were identified and total grass cover was visually determined. Plant species diversity, richness, composition, woody cover and plant densities were determined. The results indicated high concentrations of arsenic, cadmium and lead at sites closer to the smelter. There were significant differences in plant species diversity (F=8.227, df=59, p0.001), richness (F
The hierarchical cluster analysis on species presence/absence data separated the vegetation into five types. Indirect gradient analysis indicated a complex interaction of gradients which have influence the pattern in species composition; however, the direct gradient analysis indicated that heavy metal pollution, disturbance and geology accounted for a significant variation in species composition. High heavy metal concentrations at the Inside Smelter Site and Outside Smelter Site were due to proximity of these sites to the smelter while high concentrations at Abattoir Hill Site were because this site was in the direction of the prevailing wind directions. Differences in species diversity, richness and composition were due to wood cutting and pollution. Differences in vegetation structure can be attributed to a complexity of factors including pollution and wood clearing. Heavy metal toxicity contributed to poor plant development, poor recruitment and as a result there were very few small trees at the polluted sites. Geology also contributed to difference in species composition. It was concluded that heavy metal pollution influenced species composition and vegetation structure.
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Submitted in partial fulfilment of the requirements for the degree of Master of Science in Biodiversity Management and Research
Keywords
Plant diversity, Plant conservation, Mineral industries