Abstract

 The Kalamazoo River has been the subject of extensive study due to the presence of polychlorinated biphenyls (PCBs) released into the system by paper mills, as part of the office paper recycling process between the late 1950's and early 1970's. Lake Allegan, a 1,600 acre lake located downstream of the major historical release areas, is the largest water feature in the Kalamazoo River system. Because of the size of the lake and its corresponding low water velocities, the lake acts as an effective sediment trap, preventing migration of the majority of sediments further downstream. A large amount of PCB data has been collected in the lake, including a 25 year record of fish PCB concentrations, major sediment sampling events in 1993/94 and 2000, and water column PCB sampling events in 1993/94 and 2000. In addition, PCB and radioisotope coring data were recently collected at several locations in the lake. Using all available data, a weight-of-evidence approach was used to develop a conceptual model for sediment deposition and PCB transport in the lake. The analysis included calculation of time-trends and associated confidence bounds in PCB content in fish, sediment and water. In addition, cesium-137, lead-210 and PCB data from finely segmented radioisotope cores were used to develop a historical record of sediment deposition and PCB concentrations.
Analysis of trending indicated clear downward PCB trends in both fish species considered, and in surficial sediment and water column data as well. Time trend analyses also considered the effects of controlling for variation in lipid content, length and weight of fish, as well as organic carbon content in sediments. Calculated half-times are consistent with radioactive core data indicating ongoing sedimentation at rates of 1-2 cm/year, with well-defined peak PCB concentrations at depths of 25-75 cm, corresponding to peak releases of PCB in the 1960's and 70's.