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Nevertheless, some important differences were also observed.

For two of the three lakes, there was a significant difference in average sediment accumulation rate during the past 33 yrs as calculated from Pb in the recent cores.

Pb has been used for more than two decades to provide the geochronology of annually deposited sediments and to construct pollution histories.

Evidence from some lakes suggests that this radionuclide may be adequately mobile to compromise dating reliability.

Since its inception, diverse dating models have been proposed, developed, used and validated in numerous environments, but their nomenclature and formulation is not homogenous.In this work we emphasize that conceptual models used to date undisturbed sediment cores can be deduced from a single fundamental equation, which relates excess Pb concentration in sediment, its flux to the sediment surface and mass accumulation rate.From this equation, models were consistently named based on the main hypothesis used and, using a unified and logical nomenclature, dating equations were derived in detail.In all three lakes, rates calculated from Pb distributions both above and below this horizon agreed, within measurement uncertainty, in recent and older cores.Furthermore, when the older data were corrected for 20 yrs of burial, the changes in slope in Pb distributions occurred at the same depth in each pair of cores.