Behavior of sedimentary Fe and Mn in a natural wetland receiving acidic mine drainage, Pennsylvania, U.S.A.

The behavior of sedimentary Fe and Mn in a natural wetland (Pennsylvania, U.S.A.) subjected to acidic mine drainage was studied to determine the potential for long-term retention of these metals in the sediments. Five metal fractions, potentially sensitive to changes in environmental conditions and the possible association of Fe and Mn with organic C and S, were investigated. Locations of metal retention and release were evaluated using multivariate statistical techniques. Depth profiles revealed differences in both horizontal and vertical distributions of all parameters measured. The oxic sediments were described by an abundance of Fe- and Mn-oxides, organic C, and total S and virtually no dissolved Fe and Mn in the interstitial water. The anoxic zone was relatively low in Fe- and Mn-oxides with a concomitant increase in dissolved Fe and Mn in the interstitial water. Metal sulfides were low in the anoxic zone. High redox potentials (-100 mV) and high C/S ratios provided circumstantial evidence that bacterial SO₄ reduction was of minor importance in metal removal, presumably due to insufficient decomposable organic matter. Adequate decomposable organic substrates in the anoxic sediments would likely enhance the formation of Fe- sulfides and provide a permanent sink of the long-term retention of metals.