Partitioning of the net CO2 exchange using an automated chamber system reveals plant phenology as key control of production and respiration fluxes in a boreal peatland

The net ecosystem CO₂ exchange (NEE) drives the carbon (C) sink–source strength of northern peatlands. Since NEE represents a balance between various production and respiration fluxes, accurate predictions of its response to global changes require an in depth understanding of these underlying processes. Currently, however, detailed information of the temporal dynamics as well as the separate biotic and abiotic controls of the NEE component fluxes is lacking in peatland ecosystems. In this study, we address this knowledge gap by using an automated chamber system established across natural and trenching/vegetation removal plots to partition NEE into its production (i.e., gross and net primary production; GPP and NPP) and respiration (i.e., ecosystem, heterotrophic and autotrophic respiration; ER, Rh and Ra) fluxes in a boreal peatland in northern Sweden. Our results showed that daily NEE patterns were driven by GPP while variations in ER were governed by Ra rather than Rh. Moreover, we observed pronounced seasonal shifts in the Ra/Rh and above/belowground NPP ratios throughout the main phenological phases. Generalized linear model analysis revealed that the greenness index derived from digital images (as a proxy for plant phenology) was the strongest control of NEE, GPP and NPP while explaining considerable fractions also in the variations of ER and Ra. In addition, our data exposed greater temperature sensitivity of NPP compared to Rh resulting in enhanced C sequestration with increasing temperature. Overall, our study suggests that the temporal patterns in NEE and its component fluxes are tightly coupled to vegetation dynamics in boreal peatlands and thus challenges previous studies that commonly identify abiotic factors as key drivers. These findings further emphasize the need for integrating detailed information on plant phenology into process‐based models to improve predictions of global change impacts on the peatland C cycle.     

Methane Emissions from Paludified Boreal Soils in European Russia as Measured and Modelled

Spatial or temporal forest–peatland transition zones were proposed as potential hot spots of methane (CH₄) emissions. Consequently, paludified soils are an important component of boreal landscape biogeochemistry. However, their role in the regional carbon cycle remains unclear. This study presents CH₄ fluxes from two forest–peatland transition zones, two wet forest sites and two clear-cut sites which were compared to fluxes of open peatlands and dry forest. The median fluxes measured using the closed-chamber technique varied from ? 0.04 to 12.6 mg m^?2 h^?1 during three climatically different years. The annual mean CH₄ emissions of the forest–peatland transition zone were significantly lower than the fluxes of the open peatland sites, 7.9 ± 0.5 and 21.9 ± 1.6 g m^?2a^?1, respectively. The dry forest site was characterized by a small uptake of CH₄ (? 2.3 ± 0.2 g m^?2a^?1). Although clear-cut forest area drastically increased in European Russia during the last two decades, if water level depths in these forests remains below 10 cm they do not act as CH₄ sources. Fluxes of CH₄ from the transition zone sites showed a higher response to soil temperature than to water table level. Fluxes of CH₄ between the atmosphere and the two investigated peatlands were not significantly different, although a significant difference in water table level could be observed. The meteorological conditions of the investigated summers changed from being hot and dry in 2013 to cold and wet in 2014; the summer of 2015 was characterized as warmer and drier in the first half and colder and wetter in the second half. Significant differences in CH₄ fluxes were measured only between 2014 and 2013. Significant differences in CH₄ fluxes and in nonlinear regressions showed that the CH₄ fluxes of the different site types such as dry forests, transition zones and open peatlands need to be modelled separately on a landscape level. Obviously, underlying processes vary with the ecosystem and (along with regional aspects) have to be understood first before large-scale modelling is possible.     

A decade of boreal rich fen greenhouse gas fluxes in response to natural and experimental water table variability

Rich fens are common boreal ecosystems with distinct hydrology, biogeochemistry and ecology that influence their carbon (C) balance. We present growing season soil chamber methane emission (F_CH4), ecosystem respiration (ER), net ecosystem exchange (NEE) and gross primary production (GPP) fluxes from a 9‐years water table manipulation experiment in an Alaskan rich fen. The study included major flood and drought years, where wetting and drying treatments further modified the severity of droughts. Results support previous findings from peatlands that drought causes reduced magnitude of growing season F_CH4, GPP and NEE, thus reducing or reversing their C sink function. Experimentally exacerbated droughts further reduced the capacity for the fen to act as a C sink by causing shifts in vegetation and thus reducing magnitude of maximum growing season GPP in subsequent flood years by ~15% compared to control plots. Conversely, water table position had only a weak influence on ER, but dominant contribution to ER switched from autotrophic respiration in wet years to heterotrophic in dry years. Droughts did not cause inter‐annual lag effects on ER in this rich fen, as has been observed in several nutrient‐poor peatlands. While ER was dependent on soil temperatures at 2 cm depth, F_CH4 was linked to soil temperatures at 25 cm. Inter‐annual variability of deep soil temperatures was in turn dependent on wetness rather than air temperature, and higher F_CH4 in flooded years was thus equally due to increased methane production at depth and decreased methane oxidation near the surface. Short‐term fluctuations in wetness caused significant lag effects on F_CH4, but droughts caused no inter‐annual lag effects on F_CH4. Our results show that frequency and severity of droughts and floods can have characteristic effects on the exchange of greenhouse gases, and emphasize the need to project future hydrological regimes in rich fens.     

Mitigation of greenhouse gas emissions from reed canary grass in paludiculture: effect of groundwater level

Background and aims

Combination of rewetting and wetland crop cultivation (paludiculture) is pursued as a wider carbon dioxide (CO₂) mitigation option in drained peatland. However, information on the overall greenhouse gas (GHG) balance for paludiculture is lacking. We investigated the GHG balance of peatlands grown with reed canary grass (RCG) and rewetted to various extents.

Methods

Gas fluxes of CO₂, methane (CH₄) and nitrous oxide (N₂O) were measured with a static chamber technique for 10 months from mesocosms sown with RCG and manipulated to ground water levels (GWL) of 0, ?10, ?20, ?30 and ?40 cm below the soil surface. Gross primary production (GPP) was estimated from the above ground biomass yield.

Results

The mean dry biomass yield across all water table treatments was 6 Mg ha^?1 with no significant differences between the treatments. Raising the GWL to the surface decreased both the net ecosystem exchange (NEE) of CO₂ and N₂O emissions whereas CH₄ emissions increased. Total cumulative GHG emissions (for 10 months) corresponded to 0.08, 0.13, 0.61, 0.68 and 0.98 kg CO₂ equivalents m^?2 from the GWL treatments at 0, ?10, ?20, ?30 and ?40 cm below the soil surface, respectively.

Conclusions

The results showed that a reduction in total GHG emission can be achieved without losing the productivity of newly established RCG when GWL is maintained close to the surface. Further studies should address the practical constrains and long-term productivity of RCG cultivation in rewetted peatlands.     

Effects of disturbance on the carbon dioxide balance of an anthropogenic peatland in northern Patagonia

Peatlands are characterized by their large carbon (C) storage capacity and represent important C sinks globally. In southern Chile, young peatlands (few centuries old) have originated due to clearcutting or fire at forest sites with high precipitation on poorly drained soils. These novel ecosystems are called anthropogenic peatlands here. Their role in the regional C cycle remains largely unknown. Here, we present 18 months of eddy covariance measurements of net ecosystem exchange (NEE) of carbon dioxide (CO₂) in an anthropogenic peatland in northern Chiloé Island, part of which is kept undisturbed for 30–40 years, by excluding human uses, and another section of the same peatland that has been disturbed by cattle grazing and Sphagnum moss extraction. Gross primary productivity (GPP) and ecosystem respiration (R_eco) were modeled from NEE, based on measured photosynthetically active radiation and air temperature, separately for each section of the peatland. Uncertainties of the annual flux estimates were assessed from the variability of modelled fluxes induced by applying different time-windows for model development between 10 and 20 days. The undisturbed area of the peatland was on average (±?SD) a larger net CO₂ sink (NEE?=???135?±?267 g?CO₂?m^?2?year^?1) than the disturbed area (NEE?=???33?±?111 g?CO₂?m^?2?year^?1). These NEE CO₂ balances are small even though GPP and R_eco were larger compared with other peatlands. R_eco had a direct relationship with water table depth (from soil surface) and a negative relationship with soil water fraction. Our results show that the disturbance by moss extraction and cattle grazing is likely to reduce the CO₂ sink function of many anthropogenic and natural peatlands on Chiloé Island, which are subjected to the same impacts.

     

Emissions of methane from northern peatlands: a review of management impacts and implications for future management options

Northern peatlands constitute a significant source of atmospheric methane (CH₄). However, management of undisturbed peatlands, as well as the restoration of disturbed peatlands, will alter the exchange of CH₄ with the atmosphere. The aim of this systematic review and meta‐analysis was to collate and analyze published studies to improve our understanding of the factors that control CH₄ emissions and the impacts of management on the gas flux from northern (latitude 40° to 70°N) peatlands. The analysis includes a total of 87 studies reporting measurements of CH₄ emissions taken at 186 sites covering different countries, peatland types, and management systems. Results show that CH₄ emissions from natural northern peatlands are highly variable with a 95% CI of 7.6–15.7 g C m^?2 year^?1 for the mean and 3.3–6.3 g C m^?2 year^?1 for the median. The overall annual average (mean ± SD) is 12 ± 21 g C m^?2 year^?1 with the highest emissions from fen ecosystems. Methane emissions from natural peatlands are mainly controlled by water table (WT) depth, plant community composition, and soil pH. Although mean annual air temperature is not a good predictor of CH₄ emissions by itself, the interaction between temperature, plant community cover, WT depth, and soil pH is important. According to short‐term forecasts of climate change, these complex interactions will be the main determinant of CH₄ emissions from northern peatlands. Drainage significantly (p < .05) reduces CH₄ emissions to the atmosphere, on average by 84%. Restoration of drained peatlands by rewetting or vegetation/rewetting increases CH₄ emissions on average by 46% compared to the original premanagement CH₄ fluxes. However, to fully evaluate the net effect of management practice on the greenhouse gas balance from high latitude peatlands, both net ecosystem exchange (NEE) and carbon exports need to be considered.     

Non-methane biogenic volatile organic compound emissions from boreal peatland microcosms under warming and water table drawdown

Boreal peatlands have significant emissions of non-methane biogenic volatile organic compounds (BVOCs). Climate warming is expected to affect these ecosystems both directly, with increasing temperature, and indirectly, through water table drawdown following increased evapotranspiration. We assessed the combined effect of warming and water table drawdown on the BVOC emissions from boreal peatland microcosms. We also assessed the treatment effects on the BVOC emissions from the peat soil after the 7-week long experiment. Emissions of isoprene, monoterpenes, sesquiterpenes, other reactive VOCs and other VOCs were sampled using a conventional chamber technique, collected on adsorbent and analyzed by GC–MS. Carbon emitted as BVOCs was less than 1% of the CO₂ uptake and up to 3% of CH₄ emission. Water table drawdown surpassed the direct warming effect and significantly decreased the emissions of all BVOC groups. Only isoprene emission was significantly increased by warming, parallel to the increased leaf number of the dominant sedge Eriophorum vaginatum. BVOC emissions from peat soil were higher under the control and warming treatments than water table drawdown, suggesting an increased activity of anaerobic microbial community. Our results suggest that boreal peatlands could have concomitant negative and positive radiative forcing effects on climate warming following the effect of water table drawdown. The observed decrease in CH₄ emission causes a negative radiative forcing while the increase in CO₂ emission and decrease in reactive BVOC emissions, which could reduce the cooling effect induced by the lower formation rate of secondary organic aerosols, both contribute to increased radiative forcing.     

Sedge Succession and Peatland Methane Dynamics: A Potential Feedback to Climate Change

Under the warmer climate, predicted for the future, northern peatlands are expected to become drier. This drying will lower the water table and likely result in reduced emissions of methane (CH₄) from these ecosystems. However, the prediction of declining CH₄ fluxes does not consider the potential effects of ecological succession, particularly the invasion of sedges into currently wet sites (open water pools, low lawns). The goal of this study was to characterize the relationship between the presence of sedges in peatlands and CH₄ efflux under natural conditions and under a climate change simulation (drained peatland). Methane fluxes, gross ecosystem production, and dissolved pore water CH₄ concentrations were measured and a vegetation survey was conducted in a natural and drained peatland near St. Charles-de-Bellechasse, Quebec, Canada, in the summer of 2003. Each peatland also had plots where the sedges had been removed by clipping. Sedges were larger, more dominant, and more productive at the drained peatland site. The natural peatland had higher CH₄ fluxes than the drained peatland, indicating that drainage was a significant control on CH₄ flux. Methane flux was higher from plots with sedges than from plots where sedges had been removed at the natural peatland site, whereas the opposite case was observed at the drained peatland site. These results suggest that CH₄ flux was enhanced by sedges at the natural peatland site and attenuated by sedges at the drained peatland site. However, the attenuation of CH₄ flux due to sedges at the drained site was reduced in wetter periods. This finding suggests that CH₄ flux could be decreased in the event of climate warming due to the greater depth to the water table, and that sedges colonizing these areas could further attenuate CH₄ fluxes during dry periods. However, during wet periods, the sedges may cause CH₄ fluxes to be higher than is currently predicted for climate change scenarios.     

Wetland flux controls: how does interacting water table levels and temperature influence carbon dioxide and methane fluxes in northern Wisconsin?

Wetlands play a disproportionately large role in global terrestrial carbon stocks, and from 1 year to the next individual wetlands can fluctuate between carbon sinks and sources depending on factors such as hydrology, temperature, and land use. Although much research has been done on short-term seasonal to annual wetland biogeochemical cycles, there is a lack of experimental evidence concerning how the reversibility of wetland hydrological changes will influence these cycles over longer time periods. Five years of drought-induced declining water table at Lost Creek, a shrub fen wetland in northern Wisconsin, coincided with increased ecosystem respiration (R_eco) and gross primary production (GPP) as derived from long-term eddy covariance observations. Since then, however, the average water table level at this site has increased, providing a unique opportunity to explore how wetland carbon fluxes are affected by interannual air temperature differences as well as changing water table levels. Water table level, as measured by water discharge, was correlated with R_eco and GPP at interannual time scales. However, air temperature had a strong correlation with R_eco, GPP, and net ecosystem productivity (NEP) at monthly time scales and correlated with NEP at inter-annual time scales. Methane flux was strongly temperature-controlled at seasonal time scales, increasing an order of magnitude from April to July. Annual methane emissions were 51 g C m^?2. Our results demonstrate that over multi-year timescales, water table fluctuations can have limited effects on wetland net carbon fluxes and instead at Lost Creek annual temperature is the best predictor of interannual variation.     

Methane fluxes from a patterned fen of the northeastern part of the La Grande river watershed, James Bay, Canada

In northeastern Canada, at the ecotonal limit of the forest tundra and lichen woodland, a rise of the regional water table in the peatland systems was registered since Little Ice Age resulting in increasing pool compartment at the expense of terrestrial surfaces. We hypothesized that, with a mean water table closer to peat surface and higher pool density, these ecosystems would be great CH₄ emitters. In summers 2009 and 2010, methane fluxes were measured in a patterned fen located in the northeastern portion of the La Grande river watershed to determine the contribution of the different microforms (lawns, hollows, hummocks, string, pools) to the annual CH₄ budget. Mean seasonal CH₄ fluxes from terrestrial microforms ranged between 12.9 and 49.4 mg m^?2 day^?1 in 2009 and 15.4 and 47.3 mg m^?2 day^?1 in 2010. Pool fluxes (which do not include ebullition fluxes) ranged between 102.6 and 197.6 mg CH₄ m^?2 day^?1 in 2009 and 76.5 and 188.1 mg CH₄ m^?2 day^?1 in 2010. Highest fluxes were measured in microforms with water table closer to peat surface but no significant relationship was observed between water table depth and CH₄ fluxes. Spatially weighted CH₄ budget demonstrates that, during the growing season, the studied peatland emitted 66 ± 31 in 2009 and 55 ± 26 mg CH₄ m^?2 day^?1 in 2010, 79 % of which is accounted by pool fluxes. In a context where climate projections predict greater precipitations in northeastern Canada, these results indicate that this type of peatlands could contribute to modify the methane balance in the atmosphere.     

Carbon balance of rewetted and drained peat soils used for biomass production: a mesocosm study

Rewetting of drained peatlands has been recommended to reduce CO₂ emissions and to restore the carbon sink function of peatlands. Recently, the combination of rewetting and biomass production (paludiculture) has gained interest as a possible land use option in peatlands for obtaining such benefits of lower CO₂ emissions without losing agricultural land. This study quantified the carbon balance (CO₂, CH₄ and harvested biomass C) of rewetted and drained peat soils under intensively managed reed canary grass (RCG) cultivation. Mesocosms were maintained at five different groundwater levels (GWLs), that is 0, 10, 20 cm below the soil surface, representing rewetted peat soils, and 30 and 40 cm below the soil surface, representing drained peat soils. Net ecosystem exchange (NEE) of CO₂ and CH₄ emissions was measured during the growing period of RCG (May to September) using transparent and opaque closed chamber methods. The average dry biomass yield was significantly lower from rewetted peat soils (12 Mg ha^?1) than drained peat soils (15 Mg ha^?1). Also, CO₂ fluxes of gross primary production (GPP) and ecosystem respiration (ER) from rewetted peat soils were significantly lower than from drained peat soils, but net uptake of CO₂ was higher from rewetted peat soils. Cumulative CH₄ emissions were negligible (0.01 g CH₄ m^?2) from drained peat soils but were significantly higher (4.9 g CH₄ m^?2) from rewetted peat soils during measurement period (01 May–15 September 2013). The extrapolated annual C balance was 0.03 and 0.68 kg C m^?2 from rewetted and drained peat soils, respectively, indicating that rewetting and paludiculture can reduce the loss of carbon from peatlands.     

Rewetting of Cutaway Peatlands: Are We Re‐Creating Hot Spots of Methane Emissions?

Hot spots of CH₄ emissions are a typical feature of pristine peatlands at the microsite and landscape scale. To determine whether rewetting and lake construction in a cutaway peatland would result in the re‐creation of hot spots, we first measured CH₄ fluxes over a 2‐year period with static chambers and estimated annual emissions. Second, to assess whether rewetting and lake creation would produce hot spots at the landscape level, we hypothesized a number of alternative land use scenarios for the peatland following the cessation of peat extraction. Using the results from this study and other studies from literature, we calculated the global warming potential (GWP) of each scenario and the respective contribution of CH₄. The results showed that hot spots of CH₄ fluxes were observed as a consequence of microsite‐specific differences in water table (WT) position and plant productivity. CH₄ fluxes were closely related to peat temperature at 10 cm depth and WT position. Annual emissions ranged from 4.3 to 38.8 g CH₄ m^?2 yr^?1 in 2002 and 3.2 to 28.8 g CH₄ m^?2 yr^?1 in 2003. The scenario results suggest that lake creation is likely to result in the re‐creation of a hot spot at the landscape level. However, the transition from cutaway to wetland ecosystem may lead to a reduction in the GWP of the peatland.     

Vegetation heterogeneity and ditches create spatial variability in methane fluxes from peatlands drained for forestry

Drainage of peatlands for forestry starts a succession of ground vegetation in which mire species are gradually replaced by forest species. Some mire plant communities vanish quickly following the water-level drawdown; some may prevail longer in the moister patches of peatland. Drainage ditches, as a new kind of surface, introduce another component of spatial variation in drained peatlands. These variations were hypothesized to affect methane (CH₄) fluxes from drained peatlands. Methane fluxes from different plant communities and unvegetated surfaces, including ditches, were measured at the drained part of Lakkasuo mire, Central Finland. The fluxes were found to be related to peatland site type, plant community, water-table position and soil temperature. At nutrient-rich fen sites fluxes between plant communities differed only a little: almost all plots acted as CH₄ sinks (−0.9 to −0.4 mg CH₄ m⁻² d⁻¹), with the exception of Eriophorum angustifolium Honck. communities, which emitted 0.9 g CH₄ m⁻² d⁻¹. At nutrient-poor bog site the differences between plant communities were clearer. The highest emissions were measured from Eriophorum vaginatum L. communities (29.7 mg CH₄ m⁻² d⁻¹), with a decreasing trend to Sphagna (10.0 mg CH₄ m⁻² d⁻¹) and forest moss communities (2.6 mg CH₄ m⁻² d⁻¹). CH₄ emissions from different kinds of ditches were highly variable, and extremely high emissions (summertime averages 182–600 mg CH₄ m⁻² d⁻¹) were measured from continuously water-covered ditches at the drained fen. Variability in the emissions was caused by differences in the origin and movement of water in the ditches, as well as differences in vegetation communities in the ditches. While drainage on average greatly decreases CH₄ emissions from peatlands, a great spatial variability in fluxes is emerged. Emissions from ditches constantly covered with water, may in some cases have a great impact on the overall CH₄ emissions from drained peatlands.     

Vegetation Type Dominates the Spatial Variability in CH<Subscript>4</Subscript> Emissions Across Multiple Arctic Tundra Landscapes

Methane (CH₄) emissions from Arctic tundra are an important feedback to global climate. Currently, modelling and predicting CH₄ fluxes at broader scales are limited by the challenge of upscaling plot-scale measurements in spatially heterogeneous landscapes, and by uncertainties regarding key controls of CH₄ emissions. In this study, CH₄ and CO₂ fluxes were measured together with a range of environmental variables and detailed vegetation analysis at four sites spanning 300 km latitude from Barrow to Ivotuk (Alaska). We used multiple regression modelling to identify drivers of CH₄ flux, and to examine relationships between gross primary productivity (GPP), dissolved organic carbon (DOC) and CH₄ fluxes. We found that a highly simplified vegetation classification consisting of just three vegetation types (wet sedge, tussock sedge and other) explained 54% of the variation in CH₄ fluxes across the entire transect, performing almost as well as a more complex model including water table, sedge height and soil moisture (explaining 58% of the variation in CH₄ fluxes). Substantial CH₄ emissions were recorded from tussock sedges in locations even when the water table was lower than 40 cm below the surface, demonstrating the importance of plant-mediated transport. We also found no relationship between instantaneous GPP and CH₄ fluxes, suggesting that models should be cautious in assuming a direct relationship between primary production and CH₄ emissions. Our findings demonstrate the importance of vegetation as an integrator of processes controlling CH₄ emissions in Arctic ecosystems, and provide a simplified framework for upscaling plot scale CH₄ flux measurements from Arctic ecosystems.     

Effect of water table drawdown on peatland nutrient dynamics: implications for climate change

It is anticipated that a lowering of the water table and reduced soil moisture levels in peatlands may increase peat decomposition rates and consequently affect nutrient availability. However, it is not clear if patterns will be consistent across different peatland types or within peatlands given the natural range of ecohydrological conditions within these systems. We examined the effect of persistent drought on peatland nutrient dynamics by quantifying the effects of an experimentally lowered water table position (drained for a 10-year period) on peat KCl-extractable total inorganic nitrogen (ext-TIN), peat KCl-extractable nitrate (ext-NO₃ ^?), and water-extractable ortho-phosphorus (ext-PO₄ ^3?) concentrations and net phosphorus (P) and nitrogen (N) mineralization and nitrification rates at natural (control) and drained microforms (hummocks, lawns) of a bog and poor fen near Québec City, Canada. Drainage (water table drawdown) decreased net nitrification rates across the landscape and increased ext-NO₃ ^? concentrations, but did not affect net N and P mineralization rates or ext-TIN and ext-PO₄ ^3? concentrations. We suggest that the thick capillary fringe at the drained peatland likely maintained sufficient moisture above the water table to limit the effects of drainage on microbial activity, and a 20 cm lowering of the water table does not appear to have been sufficient to create a clear difference in nutrient dynamics in this peatland landscape. We found some evidence of differences in nutrient concentrations with microforms, where concentrations were greater in lawn than hummock microforms at control sites indicating some translocation of nutrients. In general, the same microtopographic differences were not observed at drained sites. The general spatial patterns in nutrient concentrations did not reflect net mineralization/immobilization rates measured at our control or drained peatlands. Rather, the spatial patterns in nutrient availability may be regulated by differences in vegetation (mainly Sphagnum moss) cover between control and drained sites and possibly differences in hydrologic connection between microforms. Our results suggest that microform distribution and composition within a peatland may be important for determining how peatland nutrient dynamics will respond to water table drawdown in northern peatlands, as some evidence of microtopographic differences in nutrient dynamics was found.     

Growing season carbon gas exchange from peatlands used as a source of vegetation donor material for restoration

The moss layer transfer technique removes the top layer of vegetation from donor sites as a method to transfer propagules and restore degraded or reclaimed peatlands. As this technique is new, little is known about the impacts of moss layer transfer on vegetation and carbon fluxes following harvest. We monitored growing season carbon dioxide (CO₂) and methane (CH₄) fluxes as well as plant communities at donor sites and neighbouring natural peatland sites in an ombrotrophic bog and minerotrophic fen in Alberta, Canada from which material was harvested between 1 and 6 years prior to the study. Plant recovery at all donor sites was rapid with an average of 72% total plant cover one growing season after harvest at the fen and an average of 87% total plant cover two growing seasons after harvest at the bog. Moss cover also returned, averaging 84% 6 years after harvest at the bog. The majority of natural peatlands in western Canada are treed and tree recruitment at the donor sites was limited. Methane emissions were higher from donor sites compared to natural sites due to the high water table and greater sedge cover. Carbon budgets suggested that the donor fen and bog sites released higher CO₂ and CH₄ over the growing season compared to adjacent natural sites. However, vegetation re-establishment on donor sites was rapid, and it is possible that these sites will return to their original carbon-cycle functioning after disturbance, suggesting that donor sites may recover naturally without implementing management strategies.     

Evidence for older carbon loss with lowered water tables and changing plant functional groups in peatlands

A small imbalance in plant productivity and decomposition accounts for the carbon (C) accumulation capacity of peatlands. As climate changes, the continuity of peatland net C storage relies on rising primary production to offset increasing ecosystem respiration (ER) along with the persistence of older C in waterlogged peat. A lowering in the water table position in peatlands often increases decomposition rates, but concurrent plant community shifts can interactively alter ER and plant productivity responses. The combined effects of water table variation and plant communities on older peat C loss are unknown. We used a full-factorial 1-m³ mesocosm array with vascular plant functional group manipulations (Unmanipulated Control, Sedge only, and Ericaceous only) and water table depth (natural and lowered) treatments to test the effects of plants and water depth on CO₂ fluxes, decomposition, and older C loss. We used Δ¹⁴C and δ¹³C of ecosystem CO₂ respiration, bulk peat, plants, and porewater dissolved inorganic C to construct mixing models partitioning ER among potential sources. We found that the lowered water table treatments were respiring C fixed before the bomb spike (1955) from deep waterlogged peat. Lowered water table Sedge treatments had the oldest dissolved inorganic ¹⁴C signature and the highest proportional peat contribution to ER. Decomposition assays corroborated sustained high rates of decomposition with lowered water tables down to 40 cm below the peat surface. Heterotrophic respiration exceeded plant respiration at the height of the growing season in lowered water table treatments. Rates of gross primary production were only impacted by vegetation, whereas ER was affected by vegetation and water table depth treatments. The decoupling of respiration and primary production with lowered water tables combined with older C losses suggests that climate and land-use-induced changes in peatland hydrology can increase the vulnerability of peatland C stores.     

Multi-decadal Changes in Water Table Levels Alter Peatland Carbon Cycling

Globally, peatlands store a large quantity of soil carbon that can be subsequently modified by hydrologic alterations from land-use change and climate change. However, there are many uncertainties in predicting how carbon cycling and greenhouse gas emissions are altered by long-term changes in hydrology. Therefore, the goal of this study was to quantify how multi-decadal manipulations of water table (WT) levels affected carbon cycling (plant production and net ecosystem exchange from three eddy covariance towers) in a peatland complex modified by levee construction, which created a wetter area up-gradient of the levee (mean WT was 12.1 cm below the surface), a dry area below the levee (36.8 cm), and an adjacent reference site not affected by the levee (21.6 cm). We found that mean total plant production was greatest in the reference site (311.9 g C m^?2 y^?1), followed by the dry site (290.5 g C m^?2 y^?1), and lowest in the wet site (227.1 g C m^?2 y^?1). Net ecosystem exchange during the growing season was negative for all sites (sink), with the wet site having the greatest sink and the dry site having the lowest sink. Ecosystem respiration increased and CH₄ emissions decreased with a decreasing WT level. This research demonstrates that human alteration of peatland WT levels can have long-term (>50 years) consequences on peatland carbon cycling.     

Nitrous oxide and methane fluxes of a pristine slope mire in the German National Park Harz Mountains

Pristine peatlands covered by Histosols (bogs and fens) with high water table and a restricted oxygen (O₂) availability are known to have low emissions of nitrous oxide (N₂O) but may be a significant source for atmospheric methane (CH₄) which are both important greenhouse gases. For the first time N₂O and CH₄ fluxes of a pristine slope mire in the German Harz Mountains have been monitored. Previously reported peatlands are characterised by anaerobic conditions due to high water table levels. Slope mires monitored here receive O₂ through slope water inflow. Gas fluxes have been monitored deploying closed chamber method on a central non-forested area and a forested area at the periphery of the slope mire. By means of groundwater piezometers water table levels, ammonium and nitrate contents as well as hydro-chemical variables like oxygen content and redox potential of the mire pore water have been concurrently measured with trace gas fluxes at both monitoring sites of the slope mire. The slope mire took up small amounts of atmospheric methane at a rate of −0.02 ± 0.01 kg C ha⁻¹ year⁻¹ revealing no significant difference between the forested and non-forested site. Higher uptake rates were observed during low water table level. In contrast to pristine peatlands influx of oxygen containing pore water into slope mire does limit reduction processes and resultant CH₄ emission. N₂O fluxes of the forested and non-forested sites of the slope mire did not differ and amounted to 0.25 ± 0.44 kg N ha⁻¹ year⁻¹. Higher emissions were observed at low water table levels and during thawing periods. In spite of favourable conditions N₂O fluxes of the slope mire have been comparable to those of pristine peatlands.     

Short-term effects of changing water table on N2O fluxes from peat monoliths from natural and drained boreal peatlands

The effect of the water table on nitrous oxide (N₂O) fluxes from peat profiles representing boreal peatlands of differing nutrient status was studied in the laboratory. Lowering of the water table in peat monoliths taken from two natural waterlogged peatlands for 14 weeks in a greenhouse at 20 °C increased the fluxes of N₂O, an effect that was enhanced further by incubation in the dark. Raising of the water table in monoliths from two drained and forested peatlands caused cessation of the N₂O fluxes from the drained peats, which had previously been sources of N₂O. It is known that N₂O fluxes have increased in peatlands drained several decades ago. The results suggest that it is not necessary for the water table to be lowered for several years to change a boreal peatland from a N₂O sink to a source of the gas. In addition to the draining of peatlands, climate change can be expected to lower ground water levels during the summertime in the boreal zone, and this could cause marked changes in N₂O fluxes from boreal peatlands by enhancing the microbial processes involved in nitrogen transformations.