The fate of stormwater-associated bacteria in constructed wetland and water pollution control pond systems

The performances of a constructed wetland and a water pollution control pon d were compared in terms of their abilities to reduce stormwater bacterial loads to recreational waters. Concentrations of thermotolerant coliforms, e nterococci and heterotrophic bacteria were determined in inflow and outflow samples collected from each system over a 6-month period. Bacterial remova l was significantly less effective in the water pollution control pond than in the constructed wetland. This was attributed to the inability of the po nd system to retain the fine clay particles (< 2 mu m) to which the bacteri a were predominantly adsorbed. Sediment microcosm survival studies showed t hat the persistence of thermotolerant coliforms was greater in the pond sed iments than in the wetland sediments, and that predation was a major factor influencing bacterial survival. The key to greater bacterial longevity in the pond sediments appeared to be the adsorption of bacteria to fine partic les, which protected them from predators. These observations may significan tly affect the choice of treatment system for effective stormwater manageme nt.