Seasonal cycling of Fe and S in a constructed wetland: The role of sulfate-reducing bacteria

The role of sulfate-reducing bacteria (SRB) in the cycling of Fe and S was studied in a young constructed wetland located in Kanata, Ontario, Canada. The wetland is a surface-flow system composed of three consecutive cells. S ediments and water samples were collected over the course of 1 year within each cell. Sediments were analyzed for the presence of SRB (using a lactate -rich medium), whereas surface and porewaters were analyzed for their conce ntrations of dissolved Fe and sulfate and for pH, Eh, and dissolved organic carbon. Lactate-using SRB were present at all three sites within the wetla nd, and the populations were largest (10(10) colony-forming units per gram of sediment) during the cold winter months, where the temperature of the wa ter was similar to 1 degrees C. The presence of high-SRB populations also c orresponded to highly anoxic conditions within the sediments and to a decre ase of sulfate concentrations, suggesting that cold temperature did not aff ect the activity of SRB. Our results indicate that Fe and S cycling in the young constructed wetland was active throughout the year, especially in the cold winter months, where large SRB populations were encountered. This sug gests that Fe removal in wetlands can be effective in temperate climates, e ven though the temperature of the water decreases drastically during the wi nter.