THE IMPORTANCE OF OXBOW LAKES TO THE FLOODPLAIN STORAGE OF POLLUTANTS

Oxbow lakes are important stores for fine-grained sediment, potentially making them critical sinks for sediment-associated pollutants. Here, we leverage an exhaustive public archive of coring data, supplemented by our data collection, to provide a quantitative assessment of the role of oxbows as off-channel sinks. We investigated loading trends of sediment-sorbed polychlorinated biphenyls (PCBs) within oxbows of the Housatonic River, an actively meandering river in western Massachusetts. Our results reveal the efficiency of oxbows as sinks, with average PCB concentrations (14.8 ppm) that are nearly twice that of the surrounding floodplain (7.56 ppm). Storage efficiency is correlated to fine-grained sediment loading; oxbow deposits contain 16% more fines than the surrounding floodplain. Even though the 5.83 km² floodplain is the largest sink of PCB-laden material, storing as much as 14.1 t of PCBs or 2.42 g m^-2, oxbows store more than 20% of all PCBs (3.63 t of PCBs or 11.2 g m^-2) whilst making up just over 5% of the floodplain surface area. Nearly 85% of the oxbow storage of PCBs occurs within the first 50 m of floodplain, making clear the significance of regular oxbow production to the off-channel storage of sediment-associated pollutants.