BIOGEOCHEMICAL PROCESSES AFFECTING METAL CYCLING ALONG THE ANIMAS RIVER
Biogeochemical cycling of metals in the Animas River was investigated using spectroscopy, microscopy, diffraction, molecular biology, and water chemistry methods. Water and sediment samples were collected 13-14 days after the Gold King Mine spill (August 5, 2015). Microbial community changes in the sediments were assessed using Next-Generation Sequencing.
Metal concentrations in the sediments are higher in the Upper Animas River watershed (mean concentrations of 108.4±1.8 mg kg-1 Pb, 32.4±0.5 mg kg-1 Cu, 729.6±5.7 mg kg-1 Zn and 51,314.6±295.4 mg kg-1 Fe in sediments from Cement Creek, the tributary of the Animas River where the spill occurred), decreasing as the Animas River flows downstream. Contrarily, microbial diversity is low upstream and it increases downstream the Animas River. Solid-phase characterization suggest that Pb, Cu, and Zn are associated with clays, Fe-(oxy)hydroxides, and metal-bearing jarosite [Me-Fe3+3(OH)6(SO4)2] which is stable under low pH. Phosphate and nitrogen species were found in water and sediments in Farmington, NM. In addition, Fe-oxidizing microorganisms were detected in the sediments from Cement Creek, while N-cycling bacteria where found in the sediments from Farmington, NM. The solubility of jarosite at near-neutral pH and biogeochemical processes occurring downstream could affect the remobilization of metals in sediments. Because the Animas River flows through different environmental systems, this study has unique implications to understand the long-term metal release caused by recurrent contamination in river basins in semi-arid regions.