Evidence of fine-grained sediment transport and deposition in Sheboygan River, Wisconsin, based on sediment core chemical tracer profiles

Fine-grained sediment transport and deposition is observed in nine dated sediment cores obtained from the Sheboygan River. The sediment cores were dated by Cs-137 and Pb-210 methods. Sediment dating was supported by a polychlorinated biphenyl (PCB) analysis and U. S. Army Corps of Engineers (USACE) hydrographic surveys from 1976 to 2002. Plots of Cs-137 activity versus depth show distinct peaks related to peak Sheboygan River discharges in the years 1966, 1975, 1979, and 1989. These peaks result from the scouring of sediments during storm discharges and the increased deposition of the fine-grained fraction of particles, including colloidal clay particles (associated with Cs-137 and, to some extent, PCBs), in place of the scoured sediments. Core SR1a, upstream of the Pennsylvania Avenue Bridge, and cores SR5-SR8, farther downstream, show continuous sedimentation (1.2-11.8 cm/yr) since the late 1950s, whereas net sediment accumulation virtually ceased after 1988 at the intermediate sites of cores SR1-SR4. The maximum PCB concentration (161 ppm) occurs in 1969 in core SR4.