Composition and distribution of suspended sediments in Lake Michigan during summer stratification

Abstract

A quantitative description of the composition and distribution of suspended sediments is a necessary prerequisite to the determination of the transport and fate of those particles and of the chemical substances associated with them. This report is the first to make such a description for materials in the Great Lakes. Suspended sediment samples were collected from Lake Michigan during August from several depths at six locations between Grand Haven, Michigan, and Milwaukee, Wisconsin. Concentrations of total suspended material range from 1.05–2.40 mg/l. Diatoms comprise nearly all of the biogenic fraction and approximately 60% of the total. Quartz plus feldspar (25%) is usually more abundant than carbonate minerals (13%), and clays are a minor component. Abundances of all constituents were higher near the shore where shoreline input provides both nutrients and minerals. Suspended materials were concentrated at the base of the thermocline and in a bottom nepheloid layer of resuspended sediment. Mineral ratios in the nepheloid layer were similar to those in the surface centimeter of bottom sediment but diatom abundance decreased markedly below the sediment-water interface. The residence time of suspended inorganic materials in Lake Michigan is about 1.8 yrs, ample time for suspended sediment grains to be distributed throughout the lake.