Zombie soil carbon: Revival of aged soil carbon into the contemporary carbon cycle of disturbed peatlands

Boreal peatlands are undergoing rapid disturbance because of climate change and human land use, potentially releasing aged organic matter that has been stored for millennia into the atmosphere and downstream ecosystems. Common disturbances in the boreal region involve peatland drainage such as forestry activities, road blocking, and peat extraction for horticultural use. Of these, peat extraction is an ideal location to study the impact of drainage on aged organic matter mobilization because the acrotelm with modern peat has been removed. In this study, we used radiocarbon analysis of DOC and gaseous emissions of CO₂ and CH₄ to understand the contribution of aged peat to the ecosystem C balance. We hypothesized that the aged peat will play a major role in vertical and horizontal C fluxes because it is easily degradable and mobilized via hydrological alteration of the peatland catchment following disturbance. Using chamber flux measurements, DOC characterization, continuous water level data, and radiocarbon analysis in three extracted peatlands in western Canada we measured vertical and horizontal C fluxes and the approximate age of C for each flux on the peat surface and in the drainage channels. We found that aged C played a significant role in both the gaseous and dissolved C emissions in the extracted peatlands which has implications for rapid loss of C to the atmosphere and downstream ecosystems because of peatland disturbance. We conclude that peat extraction sites provide an ideal setting for radiocarbon analysis to understand the fate of aged peat in the face of rapid change.