Restoration and its impact on methane dynamics in a cutover peatland

Abstract

Peatlands cover 3% of the earth's surface, with approximately 110 to 130 million hectares in Canada and are important in terms of the long-term sequestration of atmospheric carbon. In contrast to their removal of CO2 from the atmosphere, peatlands represent 15 to 30% of the total methane emissions to the atmosphere with Canadian wetlands emitting approximately 0.1 to 1 x 1010 g yr^-1. Drainage and harvesting of peatlands generally reduces CH4 emissions to the atmosphere and increases CO2 emissions by up to 400%. However, recent studies have suggested that drained peatlands may represent a larger source of atmospheric CH4 than undisturbed peatlands. In the first part of this study, potential CH4 production and oxidation was determined from natural, harvested and recently restored peat. Total depth integrated CH4 production decreased with time post harvest where CH4 production at 2-yr > 7-yr > 20-yr cutover peat. This decrease in CH4 production was a result of a decreased source of labile carbon, a decrease in the methanogenic population, and an increase in the concentration of alternative electron acceptors. Restoration has altered CH4 production processes so that total depth integrated CH4 production was 2-yr > 7-yr >RESTORED> 20-yr cutover peat. Depth dependent trends in potential CH4 oxidation and production from each peat were dependent on the water table position while substrate quality was the main difference production values between the Lac St. Jean and Bois-des-Bel peat. Comparison of CH4 fluxes over the four field seasons showed restored site bare peat and mosses did not play a significant role in CH4 emissions from the peatland. However, the overall CH4 function of the peatland was directly related to the increase in CH4 emissions from vascular vegetation, remnant ditches and newly constructed ponds which were directly attributed to an increase in labile carbon for methanogenesis provided by vegetation. CH4 fluxes from ditches and ponds suggest that these features are the largest sources of CH4 from the peatland. However, when weighting the fluxes to the areal extent of each feature, ditches become secondary to vascular vegetation in total CH4 emissions while the ponds had a minimal impact on the amount of CH4 emitted from the peatland. Furthermore, ebullition from ditches and ponds was insignificant in comparison to the diffusive fluxes. When comparing CH4 emissions from this site to natural peatland systems (~10 g CH4 m^-2 a^-1), it is evident that the site is still a much smaller source of CH4 and that the carbon and CH4 process are still changing as the pool of labile carbon increases (develops). Vegetation succession is still occurring and more time and monitoring is needed in order to determine if this site will return to similar CH4 functions as natural peatlands.