Germination and predation of Acacia karroo seeds on acid mine drainage polluted soils

Lagerwall, Dawn
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The study aims to assess the impacts of Acid Mine Drainage (AMD) polluted soils on Acacia karroo seed germination and viability, seed dry mass and predation, in comparison with trees from the same provenance growing on non-polluted soils. The study was undertaken within the Vaal River Operations mining rights area. This area is bisected by the Vaal River which separates the polluted area from the non-polluted area. Contamination of soils on the northern section of the Vaal River is a result of mining operations, historical tailings spillage as well as an existing pollution plume which has resulted in AMD polluted soils. The rehabilitation of disturbed land is often hindered due to low seedling establishment. The success of germination is one of the most important first steps for seedling establishment and growth and hence towards establishing a self-sustaining vegetation cover over disturbed areas. Dry seed mass was slightly higher from trees in non-polluted (0.051±0.009g) compared to the polluted areas (0.046±0.009g), however no significant difference was found. Seeds collected from the non-polluted area had highest proportion of seeds in the seed mass class 0.0455-0.0904g, compared to the seeds from the polluted areas which were highest in the smaller seed mass class 0.0155-0.454g. At the tree level, the Coefficient of Variation (CV) for dry seed mass was higher for seeds collected from the polluted area (20.5%) compared to the non-polluted area (17.9%), however, no significant difference was found. However, percentage seed predation was significantly lower in the polluted (35±15.76%) relative to the non-polluted areas (48±14.69%). Percentage seed germination was significantly higher in the non-polluted (92±9.35%) compared to the polluted areas (81±20.42%), with a significantly more rapid germination rate of 4.2±0.19 days compared to 4.7±0.45 days, respectively. In conclusion, despite their lower dry seed mass, seeds collected from AMD polluted soils still had high percentage germination, while exhibiting a lower percentage of seed predation compared to those growing on unpolluted soils. Due to A. karroo’s apparent tolerance to the poor conditions on the AMD polluted soils and its regeneration capabilities, it is likely to be a good species for rehabilitation of AMD polluted sites. Further studies should aim to determine seedling performance from those seeds collected from polluted areas in terms of seedling establishment, rates of growth and survival over time when established in AMD polluted soils as well as non-polluted soils, to determine their likely success.
A research report submitted to the Faculty of Science, in partial fulfilment of the requirements for the degree of Master of Science, University of the Witwatersrand, Johannesburg, March 2016.
Lagerwall, Dawn (2016) Germination and predation of Acacia karroo seeds on acid mine drainage polluted soils, University of Witwatersrand, Johannesburg, <>