A Comparative Study of Heavy Metal Concentrations in River Mouth Sediments Around the Great Lakes

Abstract

Surface and core samples of sediment from the mouths of 116 watercourses flowing into the Great Lakes system have been analyzed for ten heavy metals (lead, silver, cadmium, cobalt, copper, chromium, nickel, zinc, manganese and mercury). Most ‘undeveloped’ watercourses, especially those in Lakes Superior and Huron, are characterized by outlet sediments with low concentrations of heavy metals. Elevated levels of heavy metals occur in the outlets of most watercourses with urban-industrial activities, with the exception of those tributaries on the eastern side of Lake Michigan with glacial lakes and swamps upstream which act as sedimentation ‘sinks’ for heavy metals. Watercourses with elevated and excessive levels of heavy metals in their outlet sediments are identified. Most of the core samples showed no surface accumulation of heavy metals, probably due to dredging, shipping activities and current action in the river outlets. The lotic inputs of all the heavy metals studied, especially cadmium, chromium and mercury, are greater in the Lower Great Lakes than in the Upper Lakes. A number of significant correlations were found between the heavy metal concentrations and two of the sediment parameters, i.e., clay content and percentage loss on ignition (organic matter).