RIVER TORTUOSITY AS A DRIVER OF POLLUTANT STORAGE WITHIN POINT BARS AND FLOODPLAINS

The fate of organic pollutants in river systems has profound implications for ecological and human health. The longer such pollutants stay mobile, the greater the possibility of human exposure and incorporation into the riverine food web. Sedimentation can be a mechanism for immobilization, as organic pollutants have a tendency for adsorption onto clay surfaces and organic particles. The deposition of these materials not only prevents continual transport, but also provides a means for the gradual breakdown of deposited pollutants through microbial activity. Although the floodplain has long been identified as an important sink for fine sediment and associated pollutants, we are still unsure of the mechanisms that might focus deposition of pollutant-laden sediment. Here, we investigate the potential role of the channel planform in determining where advection-driven pollutant deposition may be concentrated. The importance of channel curvature in controlling within-channel hydraulics is clear, but we are less sure of the role of curvature in imparting an influence on where overbank flows escape onto the floodplain. We leverage an exhaustive data set collected by federal agencies that details the deposition of polychlorinated biphenyls (PCBs) along the meandering Housatonic River in western Massachusetts. The data include over 450 sediment samples from the floodplain and over 100 from the riverbed, providing a unique opportunity to assess the role of planform tortuosity in floodplain pollutant loading and within-channel storage. The latter indicates an important role for the river point bar in pollutant deposition. This work makes clear the importance of the ecosystem services provided by freely meandering rivers and their floodplains.