The Influence of Phototrophic Biomass on Fe and S Redox Cycling in an Acid Mine Drainage-Impacted System

We examined the effects of organic carbon from oxygenic photosynthetic algal biomass on the redox cycling of Fe and S in an acid mine drainage (AMD)impacted system. Fe(III)-rich sediments from the field site with abundant algae contained fewer Fe(II) oxidizing bacteria and lower rates of Fe(II) oxidation compared to sediments that did not contain abundant algae. The addition of algal biomass to sediments that did not previously contain abundant algae inhibited microbiological Fe(II) oxidation and enhanced microbiological Fe(III) and sulfate reduction. As Fe(III) reduction proceeded, sulfate was released into solution due to the reductive solubilization of Fe(III) (hydr)oxy-sulfate phases. Our results indicate that in systems where oxidative precipitation of Fe is exploited as an AMD treatment strategy, the abundant organic carbon provided by photosynthetic organisms may inhibit or reverse Fe(II) oxidation.