Investigating soil algae and cyanoprokaryotes on gold tailings material in South Africa
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Gold mine tailings material facilities are characterized by sparse vegetation and an abundance of dust. Mine tailings facilities are examples of extreme geotechnical and geochemical conditions which make it almost impossible for higher plants to establish and grow without rehabilitation intervention. In most cases higher plants such as grasses and trees are the focus areas for rehabilitation, but, having a look at something a little smaller such as biological crusts, it is seen that these micro-organisms play very important roles in any ecosystem. Various studies have shown that biological crusts, consisting of micro-organisms such as lichens, algae and cyanoprokaryotes enhance the soil quality by binding soil particles together, forming aggregates which counteract the erosive forces of wind and water. They play a part in nitrogen and carbon fixation, increase the soil surface temperature and increase the water retention of the soil. Thus, these organisms improve the overall health of the soil, which will in time encourage the successful establishment of higher plants. The aim of this study was to investigate the presence of cyanoprokaryotes and soil algae on mine tailings storage facilities that have been rehabilitated for different periods of time as well as to correlate the presence of these species with the physical and chemical characteristics of the mine tailings material. Chemical, physical and biological analyses of soil samples were done. Some of the ecologically important and dominant species were isolated and protocols were developed in order to identify the most successful manner in which to re-inoculate the organisms to a chosen substrate and how to measure biomass. Due to the immense cost of standard rehabilitation practices there is a need for a more cost effective, sustainable manner in which to protect the tailings material against the erosive forces of wind and water with as little input as possible. The influence of an organism cultured in normal Bold’s Basal medium (BBM) growth medium, BBM growth medium with half the phosphate concentration and BBM growth medium with half the nitrate concentration on the establishment of a biological soil crust (BSC) was tested. To test the influence of the inoculums already present in the tailings material and in the air, trials with mulch, water and nutrients without the addition of an organism was also investigated. This was done in the controlled environment of a glasshouse, as well as in field conditions. The biomass of the cyanoprokaryotes and algae, as well as the soil surface strength was also tested. The results show that the time of rehabilitation did not have an influence on the cyanoprokaryotes as well as algal species that occurred on the tailings material. Chlorella sp., Chlorococcum sp. and Klebsormidium sp. were present on all six sites, except on the fresh material and 15 year old material where no rehabilitation has been done. As for dominance; Chlamydomonas sp., Chlorococcum sp., Klebsormidium sp. and Phormidium sp. were dominant on all six sites except for the fresh material, where nothing grew. An array of methods exists for measuring algal biomass as a measure of growth. During the development of protocols for further use in investigating the growth of algae, the extraction solvent ethanol, for use in chlorophyll a extraction, was identified as the most sufficient. The re-inoculation of cyanoprokaryotes and soil algae onto a chosen substrate is most successful when pouring the organisms, cultured in growth medium and 0.1% agar, over the substrate. During the glasshouse trials the influence of the growth medium and growth medium with half the nitrate and half the phosphate concentrations showed that Chlamydomonas sp. produced the highest biomass when cultured in BBM. With Nostoc sp. the highest biomass occurred with culturing in BBM and BBM with half the phosphate concentration. Microcoleus vaginatus showed no significant difference when cultured in the three different growth mediums (BBM, BBM with half the nitrate concentration and BBM with half the phosphate concentration). Overall Nostoc sp. produced the highest biomass (34.33 μg/g), followed by Microcoleus vaginatus (17.05 μg/g) and Chlamydomonas sp. (6.12 μg/g). Soil surface strength, measured with a hand held penetrometer showed that Chlamydomonas sp. cultured in BBM growth medium produced the most stable crust (2.58 kg/cm2), although it had the lowest biomass measurements (6.12 μg/g). Nostoc sp. produced the highest biomass (34.44 μg/g), but had the lowest soil surface strength results (1.75 kg/cm2). Microcoleus vaginatus proved to be the species with high biomass production (17.05 μg/g), as well as high soil surface strength (2.08 kg/cm2). M. vaginatus is also a pioneer species and is therefore a good choice as primary inoculum on bare tailings material. It was decided to use Nostoc sp. in the field trials due to its high biomass and Microcoleus vaginatus due to the high soil surface strength produced. Despite the occurrence of a severe thunder storm on the afternoon of application and poor water management during the field trials the significance of water on the establishment of soil algae and cyanoprokaryotes on tailings material was determined.