Interconnected riverine-lacustrine systems as sedimentary repositories: Case study in southeast Michigan using 210Pb and 137Cs-based sediment accumulation and mixing models

Particle-reactive nuclides, such as Pb-210 and Cs-137, serve as powerful chronometric tools in the investigations and reconstruction of historical contamination in coastal marine and lacustrine systems. Towards the first systematic establishment of sediment chronologies of river channel sediments, a set of seven sediment cores from Clinton River and Lake St. Clair riverine-lacustrine system were collected and analyzed for (120)pb, Ra-226, and Cs-137 activities. Measured inventories of Pb-210(xs) and Cs-137 were similar to 2 and similar to 9 times higher than that expected from atmospheric fallout. From the measured Pb-210(xs)/Cs-137 inventory ratios, erosional input of Cs-137 was found to be significantly higher than that of Pb-210 indicating that anthropogenic watershed disturbances have resulted in accelerated sediment erosion. Good agreement between accumulation rates using Pb-210(xs) and Cs-137 using four different age models were obtained for four of the seven cores in the riverine-lacustrine environment. Average sediment mass accumulation rates, based on the Pb-210(xs) CFCS model, in the lower Clinton River (mean: 0.91 g cm(-2) yr(-1)) were generally higher than those in Lake St. Clair (mean: 0.55 g cm(-2) yr(-1)) due to a higher sediment flux and the unique riverine system characteristics. Sediment mixing coefficients, based on a Pb-210(xs) mixing model, were much higher in the river (mean: 64.9 cm(2) yr(-1)) compared to the lake (mean: 4.7 cm(2) yr(-1)), as was expected due to the frequency of perturbation and resuspension. Net accumulation of datable sediments in the Clinton River indicates that similar river channel deposits may act as repositories for the reconstruction of historical contamination and environmental changes. (C) 2011 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.