THE SELF-CLEANSING WATERS OF THE HOUSATONIC: A CASE STUDY OF AN INDUSTRIAL RIVER

Meandering rivers are characterised by their tendency to flood and migrate. Though this can create challenges when developing property or building roads on the floodplain, these natural behaviours end up producing beautifully sinuous river courses and oxbow lakes. The result is an environment defined by a rich diversity of habitats and an effective ability to capture sediment within the floodplain. This latter trait has led many to argue that meandering river floodplains have the potential to provide an important sinks for pollutants that adsorb to fine-grained particulate matter. Studies into the sequestration efficacy of the floodplain, however, are complicated by both the multifaceted pollution history and flood-control measures along many contaminated rivers. This makes the Massachusetts portion of the Housatonic River ideal for assessing the filtering potential of meandering rivers. Polychlorinated biphenyls (PCB’s), a known carcinogen, were leaked into the Housatonic by a General Electric Company facility until as recently as 1977. The contaminants were quickly mobilised by the river and transported throughout the floodplain environment. The EPA comprehensively sampled sediment from both the river and floodplain between 1998 and 2001, and we analysed this dataset involving thousands of sediment samples in a GIS framework. We observed steady downstream decreases in the concentrations of PCB-laden sediment, interrupted only by dams and impoundments. Most of the floodplain sequestration occurred within the riverbank-floodplain interface, with concentrations declining exponentially into the floodplain. Concentrations in the distal floodplain were negligible unless oxbow lakes were present. Oxbows were centres of sequestration, with concentrations equalling what was being deposited along the riverbank-floodplain interface. Our results confirm the importance of pollution capture by floodplains and indicate the need to conserve and restore the natural dynamics of meandering rivers.