Records of lead deposition in Lake Michigan sediments since 1800

Abstract

The distribution of stable lead has been determined in several Lake Michigan cores that have been dated using the /sup 210/Pb technique. A mathematical model, based on records of national and regional fuel use, is developed that accounts for the effect of aquatic residence time, processes of sedimentation, compaction, postdepositional redistribution of sediment solids, and the effect of finite core sectioning. The model gives an excellent quantitative description of the data, indicating that the lead profiles reflect the history of lead input from the burning of coal and leaded gasoline since about 1830 and 1920, respectively. The model is applied to obtain the sedimentation and lead deposition rates from stable lead distributions in undated sediment cores measured previously by others. The 1972 anthropogenic lead flux into the southern basin of the lake is determined to be 1.3 ..mu..g cm/sup -2/ yr/sup -1/ in comparison to the natural (precultural) flux of approximately 0.16 ..mu..g cm/sup -2/ yr/sup -1/. The anthropogenic lead deposited in the southern basin in 1972 is estimated to be approximately 240 metric tons as compared with an estimate of approximately 230 metric tons from air pollution fallout originating in the Chicago-Gary urban-industrial area. The measurement of both leadmore » and lead-210 fluxes in the same core may allow contributions of atmospheric lead to be distinguished from terrigenous pollution inputs. (auth)« less