Pb-210 has been used for more than two decades to provide the geochronology
of annually deposited sediments and to construct pollution histories. Evid
ence from some lakes suggests that this radionuclide may be adequately mobi
le to compromise dating reliability. This study provides one test of that p
ossibility by comparing recent measurements of Pb-210 and trace metals to o
nes carried out more than 20 yrs in the past. Cs-137 dating is used to conf
irm sediment accumulation rates in the recent cores. In the three Connectic
ut, USA, lakes studied, sediment accumulation rates changed abruptly to hig
her values between 40-50 yrs ago (increasing by factors of 2.2, 2.9, and 3.
0). In all three lakes, rates calculated from Pb-210 distributions both abo
ve and below this horizon agreed, within measurement uncertainty, in recent
and older cores. Furthermore, when the older data were corrected for 20 yr
s of burial, the changes in slope in Pb-210 distributions occurred at the s
ame depth in each pair of cores. The depth of sharp peaks in concentrations
of trace metals also matched. In general, this evidence supports the idea
that sediments in these lakes have simply been buried, without significant
diagenetic remobilization of Pb-210 and trace metals . Nevertheless, some i
mportant differences were also observed. For two of the three lakes, there
was a significant difference in average sediment accumulation rate during t
he past 33 yrs as calculated from Cs-137 and Pb-210 in the recent cores. Mo
st potential causes for this difference can be ruled out, and it appears th
at one of the two nuclides is remobilized compared to the other. There were
also significant differences in the total inventories of both Pb-210 and t
race metals (both up to 2 x) between recent and older cores in some cases.
This may be due to dissimilar sediment focusing, since it is not known for
certain whether the new cores were collected at exactly the same sites as i
n the past.