BIOGEOCHEMICAL TRANSFORMATIONS OF FE AND MN IN OXIC GROUNDWATER AND WELL WATER ENVIRONMENTS

This review presents an overview of the oxidation and precipitation of dissolved Fe(II) and Mn(II) in groundwater when exposed to surface co nditions. In water wells, these transformations may eventually result in biofouling problems and deterioration of water quality. Fe(II)-oxid ation products include poorly-ordered Fe(II)-oxides such as ferrihydri te which may be converted via solution to Fe(II)-oxyhydroxides (e.g., goethite) with time. Among Mn-oxides, a typical oxidation product is b irnessite which is structurally analogous to poorly-ordered ferrihydri te. Bacteria implicated in Fe- or Mn-oxidation in neutral-pH environme nts include Gallionella, Sphaerotilus, Leptothrix, Metallogenium, Pedo microbium spp., and magnetotactic bacteria. Very little information is available on the genera Crenothrix, Clonothrix, Toxothrix, and Sidero capsa, This review focuses on the stalked and sheathed bacteria Gallio nella, Leptothrix, and Sphaerotilus.