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Acid mine drainage (AMD) and its impacts on water resources
AMD is a mining legacy that poses a threat to the ecosystem ( Dsa et al. 2008; Limpitlaw et al. 2005; Sa´nchez Espan˜a et al. 2005). AMD resulted from the decanting of water from abandoned mines where the exposed sulfide minerals (Maso and Garces 2006) made contacts with water and oxygen. This contact initiates the oxidation of sulfide minerals, producing sulfuric acid at a certain rate (Van Rensburg 2003). The rate of acid generation is determined by various factors like for example the surface area of exposed metal sulfide, oxygen content, pH, and the bacterial activity of
Acidothiobacillus ferroxidans, Thiobacillus ferroxidans and Leprosprillum ferroxidans that directly and indirectly catalyzes the reaction involved (Akcil and Koldas 2006; Edwards et al. 2000; Schre nk et al. 1998). The reactions of acid generation are illustrated below using pyrite (FeS2) as an example, which is by far the greatest contributor in acid mine drainage. The first reaction is the oxidation of the sulfide minerals into dissolved iron, sulfate and hydrogen: 2FeS2(s) + 7O2(g) + 2H2O(l) = 2Fe2+(aq) + 4SO42−(aq) + 4H+(aq) When the surrounding environment is sufficiently oxidizing (depending on O2, pH and bacterial activity), much of the ferrous iron will be oxidized to Ferric iron (Fe(III)) 4Fe2+(aq) + O2(g) + 4H+(aq) = 4Fe3+(aq) + 2H2O(l) Ferric iron can further oxidize more pyrite into ferrous iron when in contact: FeS2(s) + 14Fe3+(aq) + 8H2O(l) = 15Fe2+(aq) + 2SO42−(aq) + 16H+(aq) This reaction generates more acid. The dissolution of pyrite by ferric iron (Fe3+), together with the oxidation of the Fe2+ constitutes a cycle of dissolution of pyrite. At low pH (between 2.3 and 3.5) Fe3+ precipitates as Fe(OH)3 and jarosite, leaving little Fe3+ in solution while simultaneously lowering pH: Fe3+(aq)+3H2O(l)Fe(OH)3 (solid)+3H+(aq) Fe(OH)3 precipitates and is identifiable as the deposit of amorphous, yellow, orange, or red deposit on stream bottoms (« yellow boy ») (Akcil and Koldas 2006).
Macroinvertebrate sampling
Macroinvertebrates were collected from the surface sediments at sampling sites 1 and 2 with an SASS net (25 cm diameter; 50 μm mesh) (Oberholster et al. 2009). The macroinvertebrates were collected from sand, rocks, sediments, stones in current (SIC), stones out of current (SOOC), and marginal vegetation (Oberholster et al. 2008), according to the protocol as detailed in the South African Scoring System (SASS) Version 5, Rapid bioassessment method for rivers (Dickens and Graham 2002). The organisms collected were identified to family level as listed on the SASS5 scoring sheet. The sum of the SASS5 scores represents the index of the river health, while the verage score per taxon (ASPT) is devided by the SASS5 score and by the number of sampled taxa
(Dickens and Graham 2002). The abundance of organisms within each family was estimated as: 1 = 1; A = 2-10; B = 10-100; C = 100-1000; D = > 1000 , while macroinvertebrate diversity was calculated using the Shannon‟s diversity index (Shannon and Weaver 1949): H = −(∑(ρi ln ρi)) (1) where (H) is Shannon‟s diversity index, the proportion of species (i) relative to the total number of species (ρi ) present in the aquatic ecosystem are calculated. The product of (ρi ln ρi) for each family in the aquatic ecosystem is summed, and multiplied by -1 to give H. This index was used in conjunction with the SASS5 index. With the aid of the SASS5 scoring system, the presence and absence of certain families could be determined at the different sampling sites.
Chapter 1 Introduction
Outline of Chapters Chapter
Chapter 3
Chapter 4 References
Chapter 2 Literature Review
Introduction
2.1 Current water conditions in South Africa
2.2 Cultural Eutrophication and Acid Mine drainage
2.3 The upper Olifants catchment
2.4 Phytoplankton and macroinvertebrates as bioindicator of anthropogenic pollution
2.5 References
Chapter 3 Habitat changes contradict historical data of macroinvertebrate assemblage in the riverine zone of Loskop Dam, South Africa Abstract
3.1 Introduction
3.2 Materials and methods
3.3 Results.
3.4 Discussion
3.5 Conclusion
3.6 References
Chapter 4 Assessing the impact of water quality on phytoplankton assemblages at Loskop Dam
Abstract
4.1 Introduction
4.2 Materials and methods
4.3 Results
4.4 Discussion
4.5 Conclusion
4.6 References
