Sulphur biogeochemistry in a mine tailings lake.

摘要

Field and laboratory investigation was carried out to determine the controls on acid generation associated with sulphur (S) oxidation in a Northern Ontario mine tailings lake (Moose Lake). Field results showed major seasonal pH drops occurred, resulting from substantial acid generation in the lower epilimnion of the lake. Within this region, diurnal rates of acid generation were depth-dependent, with maximal values associated with pronounced decreasing oxygen gradients. Acid generation was associated with oxidation of pyrrhotite particles rather than aqueous S species. Modeling results indicated that abiotic oxidation of pyrrhotite either by ferric iron or oxygen could not account for observed rates. However, model predictions assuming microbial processes agreed well with both the observed depth profile of acid generation, as well as associated rates. Microscopic imaging indicated extensive microbial colonization of epilimnetic-associated particles, and fluorescence in situ hybridization revealed that the S-oxidizing bacteria Acidithiobacillus spp. accounted for up to 46% of the total microbial community.;Laboratory experiments evaluated the coupled S speciation and acid generation associated with S oxidation by five different microbial treatments, all primarily Acidithiobacillus spp., with tetrathionate, thiosulphate and elemental sulphur as S substrates. Results showed that all microbial treatments were able to process the substrates, however acid generation rates and associated S speciation, were both microbial treatment and substrate specific, revealing differential microbial catalysis of potential S reaction arrays. Results indicated that closely phylogenetically related strains catalyze substantively different impacts on S geochemistry and that S disproportionation reactions are often a key component of microbial S pathways.;This thesis is the first to quantitatively show in situ, that microbial S oxidizing pathways are associated with higher rates of acid generation compared to abiotic processes for an acidic mine tailings lake. It also shows that S oxidation pathways and acid generation dynamics in acidic systems are strongly driven by microbial community composition which is not necessarily constrained by phylogenetic similarity.