Sediment diagenesis and porewater solute fluxes in acidic mine lakes: the impact of dissolved organic carbon additions

Abstract

Sediment diagenesis through microbial sulfate reduction is considered a critical process in the pH amelioration of acidic mine lakes, but is often limited by the availability of organic carbon. Organic substrates are therefore frequently added to mine lake sediments to stimulate sulfate reduction. Dissolved organic carbon (DOC) was added to sediment collected from three mine lakes, one (in Germany) with typically high concentrations of Fe and SO4 and another two (in Australia) with unusually low concentrations of Fe and SO4. After the DOC additions caused the dissolved oxygen concentrations in the overlying waters to fall below 50 μmol L–1, the sediment porewater at all sites progressed through the expected anaerobic respiration sequence. The paucity of Fe and SO4 in the Australian lakes did not appear to constrain microbial iron and sulfate reduction. Indeed, the low Fe concentrations appeared to promote microbial sulfate reduction in the Australian sites. In the German site, there was little evidence of sulfide production in the porewater and no changes in porewater pH profiles. In contrast, the sediment porewater from the two Australian sites exhibited sulfide production and increased porewater pH. Bioremediation of acidic lakes must consider the need to treat iron-rich water before attempting pH amelioration.