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

摘要

Particle-reactive nuclides, such as ~(210)Pb and ~(137)Cs, 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 ~(210)Pb, ~(226)Ra, and ~(137)Cs activities. Measured inventories of ~(210)Pb_(xs) and ~(137)Cs were ~2 and ~9 times higher than that expected from atmospheric fallout. From the measured ~(210)Pb_(xs)/~(137)Cs inventory ratios, erosional input of ~(137)Cs was found to be significantly higher than that of ~(210)Pb indicating that anthropogenic watershed disturbances have resulted in accelerated sediment erosion. Good agreement between accumulation rates using ~(210)Pb_(xs) and ~(137)Cs 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 ~(210)Pb_(xs) CFCS model, in the lower Clinton River (mean: 0.91 gem~(-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 ~(210)Pbxs mixing model, were much higher in the river (mean: 64.9 cm~2 yr~(-1)) compared to the lake (mean: 4.7cm~2yr~(-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.