Accumulation rates, focusing factors, and chronologies from depth profiles of 210Pb and 137Cs in sediments of the Laurentian Great Lakes

Sediment cores from 41 sites were collected from the Laurentian Great Lakes during 2010-2014, sectioned into 0.5-2.0 cm intervals, and the activities of 210Pb, 137Cs, and 226Ra were measured in the upper 25 to 40 cm of the sediment column by gamma spectrometry. Sediment mass accumulation rates (dry mass) calculated from 210Pb profiles range from 0.006 ± 0.001 to 0.59 ± 0.06 g cm−2 yr −1 and are similar to those reported in previous Great Lakes sediment studies. Sediment mass accumulation rates decreased with increasing water depth. 210Pb-based models in cores exhibiting favorable characteristics (i.e., those having the highest unsupported-210Pb activity at the sediment-water interface, exponential decrease of unsupported-210Pb with increasing depth in sediment cores, and a clear peak in 137Cs activity at some depth below the sediment-water interface) give calendar date profiles that are largely concordant with the maximum 137Cs peak activity at 1963. Sediment focusing factors derived from unsupported-210Pb inventories range from 0.09 to >5.34, and are well correlated with those derived from 137Cs inventories that range from 0.07 to 4.04, demonstrating the ubiquitous occurrence of horizontal sediment transport processes within the lakes. This more recent survey provides a Great Lakes-wide chronological framework for comparing the depositional histories and inventories of a wide variety of persistent, bioaccumulative and toxic pollutants that have been measured in the same sediment cores. This information will be useful for resolving scientific and practical issues pertaining to the environmental quality and management of contaminated sediments in the Laurentian Great Lakes ecosystem.