New Mexico Geological Society Annual Spring Meeting — Abstracts

This study investigated the effects of redox conditions on the mobilization of Pb, Cu, and Fe from sediments of an acid mine drainage (AMD)-impacted stream. Controlled laboratory microcosm experiments were conducted, integrating electron microscopy and aqueous chemistry. Microcosms containing synthetic river water (SRW) and sediments were amended with acetate and cycled through oxic-anoxic-oxic phases, each lasting 5 days (total of 15 days). STEM-EDXS analysis of the sediments revealed Pb and Cu associated with Al-silicates and jarosite. High-throughput DNA sequencing of the fungal community identified metal-tolerant genera in the sediments, including Aspergillus, Trichoderma, and Fusarium. In the microcosm experiments, Fe release was minimal during the initial oxic phase (<3 mg L⁻¹), peaked under anoxia (~250 mg L⁻¹ without acetate), and decreased in the final oxic phase (<70 mg L⁻¹). Notably, Pb concentrations consistently surpassed EPA action levels (15 µg L⁻¹), independent of redox and carbon amendment conditions. Extraction assays confirmed high water lability of Pb and Cu from sediments at an acidic pH (3.4) (Pb: 27 µg L⁻¹, Cu: 75 µg L⁻¹), with significantly lower lability at circumneutral pH (6.4) (Pb: 7 µg L⁻¹, Cu: 3 µg L⁻¹). The results highlight that Pb and Cu are easily labile under the natural acidic conditions of AMD-impacted streams, posing a risk to ecosystems and human health. Further studies are necessary to investigate the role of fungi in the biogeochemical processes affecting metal mobilization in this environment.