SEASONAL-VARIATIONS IN THE MICROBIOLOGY AND CHEMISTRY OF AN ACID-MINE DRAINAGE STREAM
Authors: Mcginness, S., Johnson DB.,
Year of publication:1993
Journal: Science of the Total Environment, , Volume: 132(1), Pages: 27-41.
Publisher: Elsevier Science Bv
An acid mine drainage stream emanating from a disused pyrite mine in North Wales was analysed over a 2-year period. Samples were routinely taken from inside the mine itself, along its flow path up to the point where it joined the river Conwy and from the river above and below this juncture. Water samples were subjected to microbiological and chemical analysis. Mean concentrations of dissolved metals and sulphate were found to decrease along the length of the stream; dissolved organic carbon remained fairly constant. Numbers of iron oxidising bacteria fell with distance from the mine, whilst neutrophilic heterotrophs increased. Highest counts of total bacteria were found in the stream within the mine, where 'acid streamer' growths were particularly abundant. A number of measured parameters displayed distinct seasonal trends. Total iron concentrations were highest in the summer (August), ferrous:ferric iron ratios peaked during winter (February). The latter showed much greater temporal variation in the acid mine drainage stream outside the mine, where seasonal effects, particularly temperatures, were more pronounced. Dissolved organic carbon was higher in August than at other times, as were total bacterial counts and numbers of iron-oxidising bacteria. The dominant iron-oxidising bacterium at all sampling sites was Thiobacillus ferrooxidans. Leptospirillum ferrooxidans accounted for between 9 and 50% of isolates. Differences in L. ferrooxidans:T. ferrooxidans ratios between sampling sites were not significant, but seasonal trends were observed, with ratios peaking in August in the stream inside the mine and November outside the mine. The acidic stream was found to have no detectable detrimental effects on the microbiology of the river Conwy. Acidophilic heterotrophic bacteria were occasionally isolated from the river, but no iron-oxidising bacteria were detected.