HR: 16:15h
AN: B42E-02    [PDF]
TI: Sulfur Oxidation, Microbes And Acidity In A Mine Tailings Lake
AU: * Warren, L A
EM: warrenl@mcmaster.ca
AF: School of Geography and Geology McMaster University, 1280 Main St. West, Hamilton, ON L8S 4K1 Canada
AU: Bernier, L
EM: berniejm@mcmaster.ca
AF: School of Geography and Geology McMaster University, 1280 Main St. West, Hamilton, ON L8S 4K1 Canada
AB: Disposal of tailings (waste rock) aqueously is a common approach at mine sites to minimize oxidation of the associated sulfur minerals (pyrrhotite, pyrite) and the associated generation of acidity that accompanies this process. The study site, Moose Lake, receives tailings runoff at a nickel mine in Northern Ontario, which has rendered the lake highly acidic (surface pH values less than 3.5) with high metal loads and on-going acid export to off-site, downstream systems. To investigate the potential influence of microbial processes for acid generation, as well as characterizing any attendant influences for metal behaviour, the biogeochemistry of Moose Lake was characterized on a seasonal and a diel basis during the summer of 2002. Physico-chemical profiles were used to identify the area of strong redox gradient across the thermocline (typically 1 to 2 metres across this zone) on each sampling day. Samples at five depths within this redox gradient, were then collected for Fe$^{3+}$/Fe$^{2+}$, SO$_{4}$$^{2-}$/H$_{2}$S, metal and microbial samples, in addition to more highly resolved Hydrolab profiling. Samples were collected both during the lighted portion of the day (10am-12pm) and at dusk (6pm-8pm) to evaluate any contributions to S and Fe cycling attributed to photosynthetic activity. Results indicate a clear seasonal increase in acidity in the upper waters of the lake: pH values dropped from 3.19 in May to 2.90 in September. Further, a strong diel trend of increasing acidity (lower pH) from mid morning to dusk was also observed for each sampling period. Biotic control on S processes appears to be important associated with the thermocline region of the lake, whilst surficial processes occurring in the upper one to three meters are more consistent with a dominant abiotic control. Both pathways contribute to acidity generation, however the controls and rates differ. These results and implications for mitigation strategies will be presented.
DE: 1045 Low-temperature geochemistry
DE: 1065 Trace elements (3670)
DE: 1806 Chemistry of fresh water
DE: 1871 Surface water quality
SC: Biogeosciences [B]
MN: 2003 Fall Meeting