Problems with the dating of sediment core using excess 210Pb in a freshwater system impacted by large scale watershed changes

Reviews and syntheses: <sup>210</sup>Pb-derived sediment and carbon accumulation rates in vegetated coastal ecosystems: setting the record straight

“…210 Pb has been shown to be an ideal tracer for dating aquatic sediments deposited during the last 100 yr: 1) providing a time frame compatible with management actions (C org requires a minimum permanence of approximately 40-150 years to be considered relevant for climate change mitigation; Marland et al, 2001); 2) 210 Pb is not affected by interannual variability (C org that naturally cycles through an ecosystem is part of the "baseline" condition; Howard et al, 2017); and 3) it enables the determination of sediment 25 accumulation rates and changes which have occurred during the last century, the period of greatest human influence on the environment (Duarte, 2014). Although several review papers have been published in recent years which have elaborated the various applications of excess 210 Pb as a tracer in terrestrial and aquatic environments (Appleby, 2001;Baskaran et al, 2014;Du et al, 2012;Kirchner and Ehlers, 1998;Mabit et al, 2014;Sanchez-Cabeza and Ruiz-Fernández, 2012;Smith, 2001), little attention has been paid to the potential limitations of the 210 Pb dating method in vegetated coastal sediments. 30…”

Sediment accumulation rates and sediment dynamics using five different methods in a well-constrained impoundment: Case study from Union Lake, Michigan

“…In a recent study from a relatively small lake in southwestern Arkansas, it was shown that the peak 137 Cs corresponded to 1963 and the penetration depth of 137 Cs corresponded to 1952, indicating no post-depositional diffusion of 137 Cs. In that case the historical peak Hg levels arising from Hg mining in the region matched with the chronology obtained from 137 Cs, but the 210 Pb xs profile did not decrease systematically with depth and this was attributed to major changes in the watershed (Baskaran et al, 2014).…”

“…The 210 Pb xs -based chronology can be affected by a number of factors that include changes in the annual atmospheric depositional flux and erosional input, sediment focusing and erosion, postdepositional disturbances of sediment core by biological and/or physical mixing, 210 Pb produced from the discharge of groundwater containing high concentrations of 222 Rn and/or 226 Ra (e.g., Baskaran et al, 2014). Because of these factors, it has been strongly recommended that there should be one other method to validate the 210 Pb xs chronology (Smith, 2001;Hancock et al, 2002).…”

“…Because the K d of Cs in freshwater is high (~10 5 cm 3 /g, e.g., Edgington and Robbins, 1990), this assumption is reasonable. The shape of the 137 Cs likely provides insight on sediment resuspension and vertical sediment mixing (e.g., Baskaran et al, 2014). Details on the basic characteristics of a Gaussian curve relevant to the 137 Cs fallout peak are given in Baskaran et al (2014).…”

“…The shape of the 137 Cs likely provides insight on sediment resuspension and vertical sediment mixing (e.g., Baskaran et al, 2014). Details on the basic characteristics of a Gaussian curve relevant to the 137 Cs fallout peak are given in Baskaran et al (2014). The mixing coefficient and the standard deviation of 137 Cs distribution are likely related when the physical and/or biological mixing alters the upper sedimentary layer.…”