Effects of seismic lines on peatland carbon cycling in boreal Alberta, Canada

Abstract

Peatlands serve as long-term carbon (C) sinks as well as a significant source of methane (CH4) to the atmosphere. Over 134,000 km2 of peatlands are in northern Alberta, a part of the boreal region of Canada where extensive industrial exploration and extraction activities are ongoing to access vast oil sands deposits. These anthropogenic disturbances, including a vast network of linear disturbances, such as seismic lines and roads, could impact long-term peatland C storage by altering ecohydrological conditions. Prior studies reported changes to hydrology, microclimatic conditions, and vegetation communities. Yet, the cumulative impact of these changes on peatland functions, that is, microbial functional activity, peat accumulation rates and carbon dioxide (CO2) and CH4 exchange is not very well understood. Due to rising concerns related to climate change and the need to develop nature-based climate interventions, peatland management should be of utmost importance to Canada, which is home to the largest global peatland C stock. We therefore measured in-situ and in-vitro soil respiration, net primary production (NPP) and litter decomposition, and CH4 emissions on eight seismic lines across one fen and two bog peatland sites affected by seismic exploration in northern Alberta and compared the results to adjacent natural areas. Soil respiration was slightly lower on seismic lines than from natural peatlands, likely due to minimal contributions of tree root respiration on the lines. Ground layer NPP was higher on the lines, but this did not offset the loss of overstory NPP. The litter decomposition rate was similar on and off the seismic line, but a shift in plant community composition towards species with more easily decomposable litter, particularly at the fen site, resulted in greater loss of litter overall. The potential peat accumulation rate, calculated as the difference between NPP and litter loss to decomposition over two years, was therefore lower on the seismic lines. This implies that recovery of an overstory in these wooded peatlands is necessary to achieve pre-disturbance C accumulation rates. Methane emissions were significantly higher on the seismic lines, increasing 176% (fens) and 261–308% (bogs) compared to the adjacent natural peatland. Higher CH4 emissions on the seismic lines were associated with warmer, wetter conditions and, at the fen site, higher sedge cover. Results from this study provide important baseline information about C cycling in peatlands affected by seismic line disturbance. Our findings contribute to accurate greenhouse gas (GHG) reporting for anthropogenic disturbances in boreal peatlands and can be used to assess the potential benefits, from a C storage perspective, of restoration efforts aimed at returning forest cover.