ACCUMULATION, INVENTORY, AND DIAGENESIS OF CHLORINATED HYDROCARBONS IN LAKE-ONTARIO SEDIMENTS

Five sediment cores were taken in 1990-1991 from the sedimentation bas ins of take Ontario and analyzed for the radionuclide Pb-210 and hydro phobic organic compounds (HOCs) in order to determine the accumulation , inventory, and diagenesis of these HOCs in the sediments. Two of the se sites were sampled earlier in 1981, allowing the study of diageneti c processes affecting these HOCs over a decade-long interval. The shap e and details of HOC sediment profiles agreed with the HOC production and usage history, despite evidence of bioturbation in the cores. The Pb-210 chronology showed a mixed depth of 2-5 cm, but mixing by deposi t-feeding oligochaetes acid benthic organisms was insufficient to homo genize the sediment over the time scale of HOC inputs. Recent HOC accu mulation rates and inventories showed significant variability among co res, which was removed when corrected for Pb-210-based sediment focusi ng. This suggests that particle-reactive compounds like HOCs are mixed and distributed evenly throughout the lake basins and that site-speci fic differences are due to differing amounts of sediment delivered via focusing of sediment to depositional basins. Comparison of 1981 and 1 990 sediment cores showed expected downcore movement of HOC profiles d ue to 9 yr of accumulated sediment mass with effectively no loss or ga in in mass.