A framework for ²¹⁰Pb model selection and its application to 37 cores from Eastern Canada to identify the dynamics and drivers of lake sedimentation rates

Abstract

Lake sedimentation rate represents a synthetic metric of ecosystem functioning. Many localized studies have reported a significant association between land use/land cover changes and lake sediment mass accumulation rates, with a few global syntheses echoing these findings at larger scales. In the literature, studies evaluating lead‐210 (210Pb) for establishing sediment chronologies will report at least one of three dating models, but the constant rate of supply (CRS) model is the most widely used. However, it is often unclear how or why this model is selected, despite its influence on the interpretation of many subsequent analyses about ecosystem dynamics and functioning. It would thus be advantageous to design an objective and semi‐automated way of choosing among dating models. We measured radioisotopic activities in 37 sediment cores across four ecozones of Eastern Canada and developed an approach to assess model fit for the three commonly applied dating models. The derived chronologies were then used to evaluate the spatial and temporal variation in sedimentation rates across four ecozones in Canada (covering a surface area of 2.2 × 106 km2). We observed a recent increase in lake sedimentation rates across most lakes, as has been observed globally, albeit with significant differences in the magnitude of sedimentation rates across ecozones. Across all lakes, we found that regional human population counts and mean annual air temperatures were significant temporal predictors of variation in mass accumulation rates. Overall, this analytical framework offers an objective approach for assessing fit and selecting among sediment age models, which contributes to a more robust quantification of sedimentation rates. With this first application, we provide a quantitative assessment of how lake sedimentation rates have varied across a northern lake‐rich region and have responded to environmental change.

Zooplankton assemblage structure and diversity since pre‐industrial times in relation to land use

“…However, this pattern seemingly did not translate into many significant functional diversity changes (Figure 4), and lakes of greater functional diversity showed less movement in the PCA through time in relation to land use (Figure 5b). It should be noted that recent increases in global sedimentation rates along with sediment compaction can influence mass accumulation rates of lake sediments (Baud et al, 2021(Baud et al, , 2022, and so our temporal local diversity declines could be partially related to more years being integrated in the bottom versus top samples. In our analysis from a subset of 27 dated full cores, we found that the top 1 cm represented on average 11 ± 9 years of deposition, whereas an average of 18 ± 11 years were integrated in the bottom 1-cm interval (for the full cores the bottom was the lowest 1-cm sample that could be dated using 210 Pb activities).…”

“…Subfossil cladoceran assemblages may also provide a more integrative, whole‐lake portrait than discrete pelagic samples of contemporary communities because the sediments deposited in the deepest part of a lake contain particles focused potentially from the entire lake basin, including the littoral zone (García‐Girón et al, 2018; Jeppesen et al, 2011). Likewise, a sediment layer 1 cm in thickness often integrates multiple years of deposition (Baud et al, 2022).…”

A significant loop of lake sedimentation state links catchment eco‐surroundings and lake biogenic regime shifts

“…In Dongting Lake, the profile variation of radionuclides in sediment cores showed a multistage decay, a mixed‐decay‐equilibrium, and a decay‐background feature, which indicated that the CRS and C‐CRS models were suitable to obtain a reliable chronology (Ran et al 2023). Lake sediment mass accumulation rates (MAR, g cm −2 yr −1 ) are reflective of both the export of materials from the watershed and of material processing and burial within lakes and, in turn, strongly influence the biogeochemical functioning of lakes (Baud et al 2022). MARs are a comprehensive metric of lake systems that can reflect lake sedimentation states and are calculated following model‐specific dating equations.…”

Congruence of water column, contemporary and pre‐industrial sediment cladoceran assemblages in 85 Canadian lakes of contrasting human impact levels

“…Consequently, when considering pelagic taxa only, it was also hypothesised (2) that water column‐contemporary sediment similarity would increase as water column samples should be dominated by pelagic taxa in most lakes. When analysing environmental drivers of species composition, we hypothesised that (3) contemporary sediment samples would be most strongly structured by environmental variables since they generally integrate seasons, multiple years of deposition, and species from the entire lake basin (Baud et al., 2022; Jeppesen et al., 2011). Pre‐industrial samples were instead expected to be structured by morphometric variables that should be mostly stable over time.…”