The effects of carbon supplementation and plant species on iron retention in mesocosm treatment wetlands

Oxides of Fe were dominant in composite sediment samples from the upper region of simulated compost wetlands exposed to acidic mine water, accounting for nearly half of substrate iron among the three sampling stations. In the middle and lower wetland regions, however, 65% of all Fe was retained as oxidizable Fe. Inferential evidence suggests that sulfate reduction was likely to be a critical process in Fe retention over at least half of the wetland length. However, overall, oxides of Fe (including amorphous and crystalline oxides) constituted the dominant phase of Fe in the wetland. The addition of a supplemental carbon source significantly stimulated both the formation of oxidizable Fe and reducible Fe in the middle and lower wetland regions, but not near the inlet. The use of effective carbon supplements is therefore recommended in field tests at acidic sites. Over the short term, the presence or species of vegetation had no effect on the partitioning of Fe phases.