Fe(III) Biomineralization in the Surface Microlayer of Acid Mine Waters Catalyzed by Neustonic Fe(II)-Oxidizing Microorganisms

The formation of thin mineral films or encrustations floating on the water surface low-flow stagnant zones acid mine drainage (AMD)-affected streams is probably among most exotic features that can be found in mining areas. However, fundamental questions about their origin (biotic vs. abiotic), structure, mineralogy, physical stability and metal-retention capacity remain unanswered. This study aims to reveal factors promoting clarify composition detail. With this purpose, major phases were studied with XRD film samples different sites Iberian Pyrite Belt district (SW Spain), oxide trace metal concentrations measured XRF and/or ICP-MS. Fe(III) minerals dominated these formations, mineralogy controlled by pH (jarosite at pH~2.0, schwertmannite 2.5–3.5, ferrihydrite > 6.0). Other have also been identified minor proportions, such as brushite khademite. These formations show an astounding concentrate, orders magnitude (×102 ×105), many metals present underlying aqueous solutions, either anionic complexes (e.g., U, Th, As, Cr, V, Sb, P) divalent cations Cu, Zn, Cd, Pb). are usually formed Fe(II)-rich acidic waters, so necessarily implies oxidation Fe(II) phases. potential involvement Fe(II)-oxidizing microorganisms was investigated through 16S rRNA gene amplicon sequencing underneath Fe(III)-rich films. sequenced reads Ferrovum (51.7 ± 0.3%), Acidithiobacillus (18.5 0.9%) Leptospirillum (3.3 0.1%), three well-known genera. contributors ferric films, although other genera likely play a role aspects sequestration, nucleation growth. waters represent hotspots biosphere/hydrosphere/atmosphere interactions great value for iron biogeochemistry redox boundaries.