Abstract
Drainage from metal-sulphide rich rocks may cause considerable environmental stress in the form of elevated sulphate and heavy metal contamination of the environment. Mine draining effects from closed mines may be abated using indigenous and introduced microbial communities for sulphate reduction and metal precipitation at the mining site. Here we characterized the general and sulphate reducing bacterial (SRB) community of Kotalahti Mine (Finland). The mine was flooded after closure and sulphate reduction and metal precipitation was induced by addition of pig manure sludge into the Vehkankuilu shaft. Water was sampled from Vehkankuilu and Ollinkuilu shafts from depths −10, −30, −70 and −100 m 15 years after the treatment. The water in the shafts differed from each other biologically and geochemically. The shafts are not directly connected except by some fracture zones, and the Ollinkuilu shaft is used as a reference for environmental monitoring. The detected bacterial communities from both shafts contained methylotrophic γ-Proteobacteria, hydrogenotrophic and methylotrophic β-Proteobacteria and fermenting bacterial clades. The concentration of SRB was low, at most 4.0 × 103 dsrB genes·mL−1, and the SRB affiliated with Desulfobulbus and Thermoanaerobacteriales clades. Despite the obvious success of the mine as an in situ bioreactor for increasing water pH and removing sulphate and heavy metals by induced sulphate reduction under suboptimal temperature, only a small portion, less than 0.5%, of the bacterial population in the mine water was SRB.
Highlights
Drainage from mines may have great effects on the environment and cause problems in the vicinity of closed mines
The bacterial communities of the samples were determined by denaturing gradient gel electrophoresis (DGGE)
Drainage and water discharge from mining areas may have severe environmental effects in form of acidification and increase in sulphate and heavy metal concentration in the environment in the vicinity of mining sites [1]. These effects have effectively been decreased by induced biological sulphate reduction in anaerobic pit lakes and flooded underground mines [9]
Summary
Drainage from mines may have great effects on the environment and cause problems in the vicinity of closed mines. Mining allows the introduction of oxygen and water to the otherwise reduced geological environment. Underground mines are often flooded in order to prevent sulphide mineral oxidation and AMD formation through isolating the sulphides from atmospheric oxygen. Mineral-oxidation and microbial activity consume dissolved oxygen present in the flooding waters [7]. Flooded open pits and mine shafts can be utilized as large sulphate reducing bioreactors to treat AMD in situ. Even though sulphate-reducing bacteria (SRB) play a crucial role in the in situ mine water treatment, only little is known about the abundance and biodiversity of microorganisms in flooded mine shafts, especially in cold and alkaline conditions. Of special interest was the abundance and diversity of the SRB in the shafts, as these microorganisms treat the mine water containing elevated concentrations of metals and sulphate. Microbial community analysis enhances the understanding of the in situ flooded reactor in Kotalahti, Finland
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