Environmental Health - Toxic Substances
U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting Charleston South Carolina March 8-12,1999--Volume 1 of 3--Contamination From Hard-Rock Mining, Water-Resources Investigation Report 99-4018A
Manganese Removal by the Epilithic Microbial Consortium at Pinal Creek near Globe, Arizona
By Eleanora I. Robbins, Timothy L. Corley, and Martha H. Conklin
This report is available in pdf format: Robbins.pdf 84KB
Interaction of an acidic mine drainage plume with subsurface material in an alluvial aquifer has released dissolved manganese [(Mn(II)] into the perennial reach of Pinal Creek near Globe, Arizona. A combination of hydrologic and biogeochemical precesses is responsible for precipitation of a fraction of the entering Mn(II) as Mn-oxyhydroxides on surficial sediments, within the streambed sediments, beneath algal mats formed on surficial sediments, and among mosses and emergent aquatic plants. This study focuses on the variety and seasonality of biological processes associated with Mn-oxyhydroxide precipitates formed on glass substrates placed in surface waters characterized by different flows and vegetation. The glass slides were emplaced monthly at a single subreach of Pinal Creek to assess epilithic attachment and Mn oxidation; epiphytic oxidation was assessed periodically also. Oxidized Mn was associated with almost every organism in the consortium at Pinal Creek, from the microscopic to the macroscopic. Epilithic bacteria, fungi, algae, and protozoans were coated with oxidized Mn; every macrophyte examined had patches of oxidized Mn. The dominant epilithic precipitation forms were around holdfasts and within secreted substances. The black holdfasts of the iron bacterium, Leptothrix discophora, and the green alga, Ulothrix sp., were doughnut-shaped forms. Expansive patches of black extracellular polysaccharides were secreted primarily by bacterial filaments and fungal hyphae. The dominant macrophytic precipitation form was clumps of oxidized Mn on mosses, green algae, and cyanobacteria. These clumps are consistent with Mn precipitation by elevated pH during photosynthesis. More Mn-oxide precipitates were found in the spring and summer months than the fall and winter, consistent with biological and chemical activity models, and more formed in swifter water than in slower moving water, consistent with oxygen elevation models. These findings provide a better understanding of the biological factors that influence natural attenuation of Mn at Pinal Creek and identify some of the complex interactions between biota, hydrologic processes, and water chemistry that need to be considered to fully assess the affects of acidic mine drainage on stream systems.