Microbiology and geochemistry of acidic sulfate-rich, metalliferrous water bodies and wetlands at the former Mynydd Parys copper mines (North Wales) were studied over a three-year period. A comparison was made between naturally-formed wetlands at Mynydd Parys and some at a former gold mine (Ridgeway, South Carolina, U.S.A.). At both mine sites, it appeared removal of soluble iron from inflowing acid mine waters was due to biological oxidation of ferrous iron, followed by hydrolysis and precipitation of ferric iron. Partial removal of sulfate and some transition metals from water flowing through the wetlands was partially attributed to bacterially-mediated sulfidogenesis. Reduction of both ferric iron and sulfate were thought to contribute to small increases in mine water pH.
Experimental wetland mesocosms were constructed to investigate the potential for enhancing amelioration of mine water using natural wetlands. The remediative potential of the Parys wetland was limited by readily degradable organic carbon and addition of sulfidic sediment resulted in improvement in metal removal. During this study, the large underground water body within the worked-out Parys mines was partially removed, and the geomicrobiology of the discharged water (ca. 275,000 m³ ) was studied. Acidophilic bacteria were abundant, predominantly the iron oxidiser Acidithiobacillus ferrooxidans. Macroscopic microbial growths were found in streams draining Mynydd Parys, and in newly-exposed underground workings. A novel β-proteobacterium was found to dominate (>90% of total cells in some cases) most of these growths. In contrast, large curtain-like growths hanging from wooden structures below ground were dominated by Acidobacteriaceae. A large number of novel heterotrophic acidophiles were isolated during the course of the study, some of which were screened for their abilities to accelerate the reductive dissolution of the ferric iron mineral schwertmannite. The results showed that the ability to reduce iron is far more widespread amongst genera of acidophilic heterotrophic bacteria than previously recognised.