The Earth Keeps the Score – Insights on the long-term carbon accumulation history in heavily degraded peatlands from Sudbury, Ontario

Peatlands are generally considered carbon (C) sinks, however, changes to the peatland’s chemistry, hydrological regime, and microbiome structure and composition, can transform these peatlands into net sources of greenhouse gases (GHG) to the atmosphere. Becoming a net GHG source is particularly exacerbated by large-scale processes such as pollution, forest fires, and increased evapotranspiration under the influence of climate change.

In this study, we evaluate the long-term soil C dynamics in four peatlands across a pollution gradient in the Greater Sudbury Area (ON), North America’s largest point source pollutant of acidic sulfate and some heavy metals during mid 20th century. Using peat C, sulfur, nitrogen, base cations, metal, and metalloid geochemistry coupled with radiocarbon dating, we contrast pollutant loading with temporally constrained C stocks and accumulation rates to identify whether a relationship exists between smelter pollutant contamination of peatlands during the industrial isochron (1880 to 1975) and the fate of their C stores. Our results indicate that while contaminant accumulation had a deleterious effect on peat structure and quality, heavy pollutant loading (high S, Ni, Cu, Pb, and As) initiated an increase in the apparent C accumulation rates. This increase could have been driven by a number of processes, such as suppression of microbial decomposer activity and shifts in species composition from Sphagnum-dominated poor fen to Ericaceous shrub-graminoid fen, the latter producing more C-dense woody peat. However, our study also indicates that downward translocation of pollutants led to a substantial post-depositional loss of C from older (deeper) peats.