Pore Water Profiles and Early Diagenesis of Mn, Cu, and Pb in Sediments from Large Lakes

Abstract

Mn Cu and Pb were measured in pore waters at a site in the Caribou sub-basin Lake Superior. The pore water profiles show evidence for the post-depositional mobility of the metals, consistent with interpretations made from sediment concentration profiles. The pore water and sediment concentration profiles of Mn appear to be diagenetically linked. Diagenetic modeling results indicate that the measured profiles are not in a steady-state relationship. The cause of the non-steady-state conditions is unclear but may be related to recent changes in sedimentation rates and in Mn 2+ oxidation rates. Flux estimates for Cu and Pb show that these metals could be diffusing from the sediment to overlying water. The decomposition of organic matter is suggested as a source for the metals. A significant amount of Cu and Pb brought to the sediment surface during sedimentation appears to be recycled to the pore waters. This suggests that concentration profiles of these metals in the sediment may not be reliable indicators of the timing and amounts of anthropogenic metal input to Lake Superior.