1999 GSA Annual Meeting -- Denver, Colorado
1999 GSA Annual Meeting -- Denver, Colorado
Author(s): SPRATT, Henry G., Jr., Univ. of Tennessee, Chattanooga, TN 37403, henry-spratt@utc.edu; STANTON, Mark R., U.S.G.S, Minerals Resources Team, Denver, CO; KOCH, Joshua C., HALLETT, Ian E., WELLS, Rachel B., and COHN, Corey A., S.E.S. Program, Ft. Lewis College, Durango, CO.
Keywords: Acid-Rock-Drainage, Water-Quality, Anthropogenic, Natural, Thiobacilli
The relative influence of natural vs. anthropogenic sources of acid rock drainage was investigated at both abandoned mine sites and natural ferricrete- or iron-oxide-containing wetlands located in the upper Animas river system near Silverton, CO. The mine sites, all located at approximately 3,200 m elevation, had been abandoned between 20 and 50 years prior to sampling. Water quality parameters determined included pH, Fe(tot), Fe(II), Fe(III), conductivity, dissolved oxygen, and sulfate. Simple comparisons of biotic habitat, including stream/bog invertebrates and riparian plant species diversity were also made at each site to assess the local ecosystems. Riparian diversity ranged from 3 to 15 species. Stream/bog invertebrates tended to be minimal to non-existent. Major differences were observed in conductivity [550 vs. 1100 micro S/cm], Fe(tot) [13 vs. 68 ppm], and sulfate [200 vs. 725 ppm]; the significantly greater values for each parameter were from anthropogenic sites. Temperature, pH, and dissolved oxygen were not significantly different between natural and anthropogenic sites. The higher concentration of Fe(tot) draining from anthropogenic sites was due almost entirely to Fe(III) because Fe(II) coming from all sites was essentially equal. This data suggests that some factor (or factors) related to the anthropogenic sites influences the concentrations of Fe(III) and sulfate present at these sites. Preliminary measurements of two species of sulfide and Fe(II) oxidizing bacteria (Thiobacillus thiooxidans and T. ferrooxidans) indicate that the anthropogenic sites have greater numbers of both species present in their substrates. Overall, this data suggests that anthropogenic influences in areas with an abundance of sulfidic minerals may stimulate sulfide/Fe(II)-oxidizing bacteria, resulting in greater release of metals and acidity than would occur from the relatively undisturbed natural sites.
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