Ecology of sulfate-reducing bacteria in an iron-dominated, mining-impacted freshwater sediment

A legacy of lead and silver mining in its headwaters left Lake Coeur d'Alene, Idaho with a sediment body that is highly reduced and contains up to 100 g kg ^-1 iron and a smaller fraction of chemically active sulfide phases. The dynamic character of these sulfides and their importance for the sequestering of contaminating trace elements prompted this study of the sulfate-reducing bacteria (SRB) involved in their production. We estimated parameters indicative of the distribution and activity of SRB in relation to season, site, and depth. Most probable number estimates and quantitative PCR assays of an SRB-specific functional gene, α-adenosine 5′-phosphosulfate reductase, indicated 10 ³ to 10 ⁶ cultivable cells and 10 ⁵ to 10 ⁷ gene copy numbers g ^-1 dry wt sediment, respectively. Although culture-based estimates of SRB abundance correlated poorly with site, season, depth, total S, or pore water SO ₄, nonculture-based estimates of SRB abundance were markedly higher at contaminated sites and positively correlated with pore water SO ₄. Ex situ estimates of ³⁵SO ₄ respiration and acid volatile sulfi des abundance also showed strong among-site effects, indicating elevated sulfidogenesis at contaminated sites. These observations support the view that biogenic sulfides may act in concert with reduced iron to retain soluble metal(loid)s in the solid phase.