Steady and ebullitive methane fluxes from active, restored and unrestored horticultural peatlands

Peatlands used for horticultural peat extraction lose their ecological function of carbon accumulation. While their restoration has been shown to increase methane (CH4) flux compared to unrestored sites, the time required for CH4 balance to recover and the factors affecting the recovery remain unclear. We quantified CH4 emissions from restored sites with different time since restoration efforts began (5, 8 and 25 years prior to the study), an unrestored post-extraction (Unrestored) and actively extracted (Active) sites, and compared them to CH4 emission from a natural boreal bog (Natural). All study sites were located within one horticulture peatland complex in central Alberta, Canada. Both steady (diffusive and steady ebullitive) fluxes and abrupt ebullitive events were determined using manual chambers and a portable greenhouse gas analyzer. Methane emissions were greater at the restored sites than at the Natural, Unrestored, and Active sites. Abrupt ebullition occurred only at two restored sites that were flooded/water saturated, dominated by vascular plants, and had the highest steady fluxes. Ebullition accounted for 7% of total CH4 emission at the site restored in 1991 (25-26 years postrestoration), and 6% at the site restored in 2012 (4-5 years post-restoration). Despite shallow water table and dense sedge cover, the third restored site (7-8 years post-restoration), showed no abrupt ebullition and mean steady flux lower than at the Natural site, likely caused by peat geochemistry. At sites where it occurred, ebullition was significantly positively but weakly correlated with CH4 flux, concentration of CH4 in pore water, soil temperature, water table (WT), gross ecosystem production , and percentage cover of moss. Steady CH4 fluxes were higher when soil temperature at 20 cm depth was higher, WT shallow, and with greater plant productivity and cover of graminoids, but lower with higher shrub cover. Peat chemical characteristics can supersede these environmental factors and suppress CH4 emission even in restored, wet, and sedge-dominated sites. Restored sites with more fen-like conditions (wet and sedge-dominated) are likely to have abrupt ebullition events and higher CH4 fluxes than undisturbed bogs, with local controls seemingly more important than time since restoration on resulting CH4 emission.

Automated summary

Research shows that restored wetland areas have higher methane emissions, with abrupt ebullition events occurring in areas with high water saturation, dominance of vascular plants, and high steady fluxes. Ebullition events are correlated with factors such as CH4 flux, CH4 concentration in pore water, soil temperature, water table, plant productivity, and vegetation cover.