• Energy Research

Abstract Restoration of peatlands after peat extraction could be a benefit to the climate system. However a multi-year ecosystem-scale assessment of net carbon (C) sequestration is needed. We investigate the climate impact of active peatland restoration (rewetting and revegetating) using a chronosequence of C gas exchange measurements across post-extraction Canadian peatlands. An atmospheric perturbation model computed the instantaneous change in radiative forcing of CO2 and CH4 emissions/uptake over 500 years. We found that using emission factors specific to an active restoration technique resulted in a radiative forcing reduction of 89% within 20 years compared to IPCC Tier 1 emission factors based on a wide range of rewetting activities. Immediate active restoration achieved a neutral climate impact (excluding C losses in the removed peat) about 155 years earlier than did a 20 year delay in restoration. A management plan that includes prompt active restoration is key to utilizing peatland restoration as a climate change mitigation strategy.

Northern peatlands are significant stocks of terrestrial soil carbon, and it has been predicted that warmer temperatures and lower water tables resulting from climate change will convert these ecosystems into sources for atmospheric carbon dioxide (CO2). However, these predictions do not consider the potential for hydrologically induced ecological succession or the spatial variability of carbon accumulation rates between different microforms in peatlands. To address these issues, the vegetation community was described, and the rates of gross ecosystem photosynthesis (GEP), ecosystem respiration (Rtot) and net ecosystem CO2 exchange were determined along poor fen microtopographic gradients at a control site and at a site which experienced a water table drawdown of ∼20 cm 8 years prior to the study (drained). Sampling plots within these sites were classified as microforms of hummocks, lawns, or hollows. The coverage of Sphagnum moss declined on drained hummocks, drained lawns were invaded by sedges, and hollows shifted from open water plots at the control site to Sphagnum‐dominated plots with sparse vascular plant cover at the drained site. As a result, Rtot was significantly greater at the drained site at all microforms while maximum rates of GEP declined at drained hummocks and were enhanced at drained lawns and hollows compared to similar control microforms. These results suggest that predictions about the response of northern peatland carbon exchange to climate change must consider the interaction between ecology and hydrology and the differential responses of microforms related to their initial ecohydrological conditions.

AbstractArctic and alpine tundra ecosystems are large reservoirs of organic carbon1,2. Climate warming may stimulate ecosystem respiration and release carbon into the atmosphere3,4. The magnitude and persistency of this stimulation and the environmental mechanisms that drive its variation remain uncertain5–7. This hampers the accuracy of global land carbon–climate feedback projections7,8. Here we synthesize 136 datasets from 56 open-top chamber in situ warming experiments located at 28 arctic and alpine tundra sites which have been running for less than 1 year up to 25 years. We show that a mean rise of 1.4 °C [confidence interval (CI) 0.9–2.0 °C] in air and 0.4 °C [CI 0.2–0.7 °C] in soil temperature results in an increase in growing season ecosystem respiration by 30% [CI 22–38%] (n = 136). Our findings indicate that the stimulation of ecosystem respiration was due to increases in both plant-related and microbial respiration (n = 9) and continued for at least 25 years (n = 136). The magnitude of the warming effects on respiration was driven by variation in warming-induced changes in local soil conditions, that is, changes in total nitrogen concentration and pH and by context-dependent spatial variation in these conditions, in particular total nitrogen concentration and the carbon:nitrogen ratio. Tundra sites with stronger nitrogen limitations and sites in which warming had stimulated plant and microbial nutrient turnover seemed particularly sensitive in their respiration response to warming. The results highlight the importance of local soil conditions and warming-induced changes therein for future climatic impacts on respiration.

AbstractAcross Canada's boreal forest, linear disturbances, including cutlines such as seismic lines and roads, crisscross the landscape to facilitate resource exploration and extraction; many of these linear disturbances cross peatland ecosystems. Changes in tree canopy cover and the compression of the peat by heavy equipment alter local thermal, hydrological, and ecological conditions, likely changing carbon exchange on the disturbance, and possibly in the adjacent peatland. We measured bulk density, water table, soil temperature, plant cover, and CO2 and CH4 flux along triplicate transects crossing a winter road through a wooded fen near Peace River, Alberta, Canada. Sample plots were located 1, 5, and 10 m from the road on both sides with an additional three plots on the road. Productivity of the overstory trees, when present, was also determined. The winter road had higher bulk density, shallower water table, higher graminoid cover, and thawed earlier than the adjacent peatland. Tree productivity and CO2 flux varied between the plots, and there was no clear pattern in relation to distance from the road. The plots on the winter road acted as a greater CO2 sink and greater CH4 source compared to the adjacent peatland with plots on the winter road emitting on average (standard error) 479 (138) compared to 41 (10) mg CH4 m−2 day−1 in the adjacent peatland. Considering both gases, global warming potential increased from 70 to 250 g CO2e m−2 year−1 in the undisturbed area to 2100 g CO2e m−2 year−1 on the winter road. Although carbon fluxes on any given cutline through peatland will vary depending on level of compaction, line width and vegetation community shifts, the large number of linear disturbances in Canada's boreal forest and slow recovery on peatland ecosites suggest they could represent an important anthropogenic greenhouse gas source.

Northern peatlands store globally significant amounts of soil carbon that could be released to the atmosphere under drier conditions induced by climate change. We measured forest floor respiration (RFF) at hummocks and hollows in a treed boreal bog in Alberta, Canada and partitioned the flux into aboveground forest floor autotrophic, belowground forest floor autotrophic, belowground tree respiration, and heterotrophic respiration using a series of clipping and trenching experiments. These fluxes were compared to those measured at sites within the same bog where water‐table (WT) was drawn down for 2 and 12 years. Experimental WT drawdown significantly increased RFF with greater increases at hummocks than hollows. Greater RFF was largely driven by increased autotrophic respiration driven by increased growth of trees and shrubs in response to drier conditions; heterotrophic respiration accounted for a declining proportion of RFF with time since drainage. Heterotrophic respiration was increased at hollows, suggesting that soil carbon may be lost from these sites in response to climate change induced drying. Overall, although WT drawdown increased RFF, the substantial contribution of autotrophic respiration to RFF suggests that peat carbon stocks are unlikely to be rapidly destabilized by drying conditions.

AbstractChanges in atmospheric temperature and lowering in water‐table (WT) are expected to affect peatland nutrient dynamics. To understand the response of peatland nitrogen (N) and phosphorus (P) dynamics to warming and drainage in a continental wooded‐bog of hummock–hollow microtopography, we compared three sites: (a) control, (b) recently drained (2–3 years; experimental), and (c) older drained (12–13 years; drained), during 2013. The WT was lowered at experimental and drained sites to 74 and 120 cm, respectively, whereas a warming of ~1 °C was created at one half of the microforms using open‐top chambers. Responses of peat total inorganic nitrogen (TIN = nitrate nitrogen [NO3−‐N] + ammonium nitrogen [NH4+‐N]) and phosphate‐P (PO43−‐P) pools and vegetation C:N ratio, δ13C and δ15N to the experimental treatments were investigated across sites/microforms and over time. Peat TIN available and extractable pools increased with deepening of WT and over time and were greater at hummocks relative to hollows. In contrast, the PO4 pools increased with short‐term drainage but reverted to very close to their original (control) nutrient values in the longer term. The WT and warming driven change in the peat TIN pool was strongly reflected in the vascular vegetation C:N ratio and shrub δ13C and δ15N, whereas moss nutrient dynamics did not vary between sites. Therefore, we suggest that atmospheric warming combined with WT deepening can increase availability of mineral N and P, which then can be reflected in vascular vegetation and hence modify the productivity and ecosystem functioning of the northern midlatitude continental wooded bogs in the long term.