Lakes quietly bury carbon in their sediments, a service that has helped regulate the climate for millennia. A study in Environmental Research Letters, led by Jean-François Lapierre of Université de Montréal's Department of Biological Sciences with Aude Flamand, Julie Talbot, Adam J. Heathcote and Candice Aulard, asks how far human activity has pushed this function from its natural state, comparing carbon accumulation over the past 11,000 years with trends over the last 150.
Rather than collecting new cores, the team reanalysed existing sediment datasets, many of them incomplete, building a predictive model linking sediment density to organic matter content that was better suited to organic-rich boreal lakes than existing tools. Reconciling radiocarbon dating of ancient layers with lead-210 dating of recent ones posed a further methodological challenge, since the two are rarely combined within a single core.
The results reframe the problem. Climate fluctuations occurred throughout the Holocene, yet the largest shifts in accumulation rates came in recent centuries, intensifying from around 1850 with industrialisation. Instead of the uniformly higher accumulation they expected, the researchers found greater variability, including sporadic drops, suggesting lakes are becoming more sensitive to disturbance. The team, which worked with Hydro-Québec and was funded by NSERC, argues that carbon footprints should be judged against this natural baseline, and plans to model the drivers behind the shift.