Climate change effects on carbon and nitrogen mineralization in peatlands through changes in soil quality

Climate change will directly affect carbon and nitrogen mineralization through changes in temperature and soil moisture, but it may also indirectly affect mineralization rates through changes in soil quality. We used an experimental mesocosm system to examine the effects of 6‐year manipulations of infrared loading (warming) and water‐table level on the potential anaerobic nitrogen and carbon (as carbon dioxide (CO₂) and methane (CH₄) production) mineralization potentials of bog and fen peat over 11 weeks under uniform anaerobic conditions. To investigate the response of the dominant methanogenic pathways, we also analyzed the stable isotope composition of CH₄ produced in the samples. Bog peat from the highest water‐table treatment produced more CO₂ than bog peat from drier mesocosms. Fen peat from the highest water‐table treatment produced the most CH₄. Cumulative nitrogen mineralization was lowest in bog peat from the warmest treatment and lowest in the fen peat from the highest water‐table treatment. As all samples were incubated under constant conditions, observed differences in mineralization patterns reflect changes in soil quality in response to climate treatments. The largest treatment effects on carbon mineralization as CO₂ occurred early in the incubations and were ameliorated over time, suggesting that the climate treatments changed the size and/or quality of a small labile carbon pool. CH₄ from the fen peat appeared to be predominately from the acetoclastic pathway, while in the bog peat a strong CH₄ oxidation signal was present despite the anaerobic conditions of our incubations. There was no evidence that changes in soil quality have lead to differences in the dominant methanogenic pathways in these systems. Overall, our results suggest that even relatively short‐term changes in climate can alter the quality of peat in bogs and fens, which could alter the response of peatland carbon and nitrogen mineralization to future climate change.     

Recovery of Methanogenesis Following Summer Drought in Soils from Two Cool Temperate Peatlands,New York State,USA

Following a summer drought, intact cores of peat soil from two cool temperate peatlands (a rain-fed bog and a groundwater-fed swamp) were exposed experimentally to three different water table levels. The goal was to examine recovery of anaerobic methanogenesis and to evaluate peat soil decomposition to methane (CH₄), carbon dioxide (CO₂), and dissolved organic carbon (DOC) upon rewetting. Methane emission from soils to the atmosphere was greatest (mean = 80 μmol m^?2 s^?1) when the entire peat core was rewetted quickly; emission was negligible at low water level and when peat cores were rewetted gradually. Rates of CO₂ emission (mean = 1.0 μmol m^?2 s^?1) were relatively insensitive to water level. Concentrations of CH₄ in soil air spaces suggest that onset of methanogenesis induces, but later represses, aerobic oxidation of CH₄ above the water table. Concentrations of CO₂ suggest production at the soil surface of swamp peat versus at greater depths in bog peat. Portions of peat soil incubated in vitro without oxygen (O₂) exhibited a lag before the onset of methanogenesis, and the lag time was less in peat from the cores rewetted quickly. The inhibition of methanogenesis by the selective inhibitor 2-bromoethanesulfonic acid (BES) decreased CO₂ production by 20 to 30% but resulted in an increase in concentrations of DOC by 2 to 5 times. The results show that methanogens in peat soils tolerate moderate drought, and recovery varies among different peat types. In peat soils, the inhibition of methanogenesis might enhance DOC availability.     

Change in fluxes of carbon dioxide,methane and nitrous oxide due to forest drainage of mire sites of different trophy

Northern peatlands accumulate atmospheric CO₂ thus counteracting climate warming. However, CH₄ which is more efficient as a greenhouse gas than CO₂, is produced in the anaerobic decomposition processes in peat. When peatlands are taken for forestry their water table is lowered by ditching. We studied long-term effects of lowered water table on the development of vegetation and the annual emissions of CO₂, CH₄ and N₂O in an ombrotrophic bog and in a minerotrophic fen in Finland. Reclamation of the peat sites for forestry had changed the composition and coverage of the field and ground layer species, and increased highly the growth of tree stand at the drained fen. In general, drainage increased the annual CO₂ emissions but the emissions were also affected by the natural fluctuations of water table. In contrast to CO₂, drainage had decreased the emissions of CH₄, the drained fen even consumed atmospheric CH₄. CO₂ and CH₄ emissions were higher in the virgin fen than in the virgin bog. There were no N₂O emissions from neither type of virgin sites. Drainage had, however, highly increased the N₂O emissions from the fen. The results suggest that post-drainage changes in gas fluxes depend on the trophy of the original mires.     

Effect of water table on greenhouse gas emissions from peatland mesocosms

Peatland landscapes typically exhibit large variations in greenhouse gas (GHG) emissions due to microtopographic and vegetation heterogeneity. As many peatland budgets are extrapolated from small-scale chamber measurements it is important to both quantify and understand the processes underlying this spatial variability. Here we carried out a mesocosm study which allowed a comparison to be made between different microtopographic features and vegetation communities, in response to conditions of both static and changing water table. Three mesocosm types (hummocks?+?Juncus effusus, hummocks?+?Eriophorum vaginatum, and hollows dominated by moss) were subjected to two water table treatments (0–5 cm and 30–35 cm depth). Measurements were made of soil-atmosphere GHG exchange, GHG concentration within the peat profile and soil water solute concentrations. After 14 weeks the high water table group was drained and the low water table group flooded. Measurement intensity was then increased to examine the immediate response to change in water table position. Mean CO₂, CH₄ and N₂O exchange across all chambers was 39.8 μg m^?2 s^?1, 54.7 μg m^?2 h^?1 and ?2.9 μg m^?2 h^?1, respectively. Hence the GHG budget was dominated in this case by CO₂ exchange. CO₂ and N₂O emissions were highest in the low water table treatment group; CH₄ emissions were highest in the saturated mesocosms. We observed a strong interaction between mesocosm type and water table for CH₄ emissions. In contrast to many previous studies, we found that the presence of aerenchyma-containing vegetation reduced CH₄ emissions. A significant pulse in both CH₄ and N₂O emissions occurred within 1–2 days of switching the water table treatments. This pulsing could potentially lead to significant underestimation of landscape annual GHG budgets when widely spaced chamber measurements are upscaled.     

Carbon fluxes in forested bog margins along a human impact gradient: could vegetation structure be used as an indicator of peat carbon emissions?

Bog ecosystems are sensitive to anthropogenic disturbance, including drainage and air pollution. Carbon (C) balance measurements to determine the effect of disturbance on bog functioning are laborious; therefore reliable proxies for C fluxes that could facilitate upscaling from single studies to a larger scale would be valuable. We measured peat CO₂ emissions (R _s), CH₄ efflux and vegetation characteristics in four bog areas that formed a gradient from pristine to severely disturbed peatlands, affected by drainage, peat mining, alkaline air pollution and underground oil-shale mining. We expected that sites experiencing higher human impact (i.e., the vegetation was more distinct from that of a natural bog) would have higher R _s and lower CH₄ emissions, but differences in peat C emissions between the most disturbed and pristine sites were not significant. Growing period median R _s ranged from 0.5 to 2.2 g C m^?2 day^?1 for our plots; methane emissions, measured from July to December were an order of magnitude lower, ranging from ?5.9 to 126.7 mg C m^?2 day^?1. R _s and CH₄ emissions were primarily determined by water table depth, as was tree stand productivity. Therefore, stand structural parameters could potentially be good indicators of soil C emissions from poorly drained forested bogs.     

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 fluxes from a tropical peat swamp forest floor

A tropical ombrotrophic peatland ecosystem is one of the largest terrestrial carbon stores. Flux rates of carbon dioxide (CO₂) and methane (CH₄) were studied at various peat water table depths in a mixed‐type peat swamp forest floor in Central Kalimantan, Indonesia. Temporary gas fluxes on microtopographically differing hummock and hollow peat surfaces were combined with peat water table data to produce annual cumulative flux estimates. Hummocks formed mainly from living and dead tree roots and decaying debris maintained a relatively steady CO₂ emission rate regardless of the water table position in peat. In nearly vegetation‐free hollows, CO₂ emission rates were progressively smaller as the water table rose towards the peat surface. Methane emissions from the peat surface remained small and were detected only in water‐saturated peat. By applying long‐term peat water table data, annual gas emissions from the peat swamp forest floor were estimated to be 3493±316 g CO₂ m^?2 and less than 1.36±0.57 g CH₄ m^?2. On the basis of the carbon emitted, CO₂ is clearly a more important greenhouse gas than CH₄. CO₂ emissions from peat are the highest during the dry season, when the oxic peat layer is at its thickest because of water table lowering.     

Functional-Structural Analysis of Nitrogen-Cycle Bacteria in a Hypersaline Mat from the Omani Desert

Anaerobic microbial activity in northern peat soils most often results in more carbon dioxide (CO ₂ ) production than methane (CH₄) production. This study examined why methanogenic conditions (i.e., equal molar amounts of CH₄ production and CO₂ production) prevail so infrequently. We used peat soils from two ombrotrophic bogs and from two rheotrophic fens. The former two represented a relatively dry bog hummock and a wet bog hollow, and the latter two represented a forested fen and a sedge-dominated fen. We quantified gas production rates in soil samples incubated in vitro with and without added metabolic substrates (glucose, ethanol, H₂/CO₂). None of the peat soils exhibited methanogenic conditions when incubated in vitro for a short time (< 5 days) and without added substrates. Incubating some samples > 50 days without added substrates led to methanogenic conditions in only one of four experiments. The anaerobic CO₂:CH₄ production ratio ranged from 5:1 to 40:1 in peat soil without additions and was larger in samples from the dry bog hummock and forested fen than the wet bog hollow and sedge fen. Adding ethanol or glucose separately to peat soils led to methanogenic conditions within 5 days after the addition by stimulating rates of CH₄ production, suggesting CH₄ production from both hydrogenotrophic and acetoclastic methanogenesis. Our results suggest that methanogenic conditions in peat soils rely on a constant supply of easily decomposable metabolic substrates. Sample handling and incubation procedures might obscure methanogenic conditions in peat soil incubated in vitro.     

High emissions of greenhouse gases from grasslands on peat and other organic soils

Drainage has turned peatlands from a carbon sink into one of the world's largest greenhouse gas (GHG) sources from cultivated soils. We analyzed a unique data set (12 peatlands, 48 sites and 122 annual budgets) of mainly unpublished GHG emissions from grasslands on bog and fen peat as well as other soils rich in soil organic carbon (SOC) in Germany. Emissions and environmental variables were measured with identical methods. Site‐averaged GHG budgets were surprisingly variable (29.2 ± 17.4 t CO₂‐eq. ha^?1 yr^?1) and partially higher than all published data and the IPCC default emission factors for GHG inventories. Generally, CO₂ (27.7 ± 17.3 t CO₂ ha^?1 yr^?1) dominated the GHG budget. Nitrous oxide (2.3 ± 2.4 kg N₂O‐N ha^?1 yr^?1) and methane emissions (30.8 ± 69.8 kg CH₄‐C ha^?1 yr^?1) were lower than expected except for CH₄ emissions from nutrient‐poor acidic sites. At single peatlands, CO₂ emissions clearly increased with deeper mean water table depth (WTD), but there was no general dependency of CO₂ on WTD for the complete data set. Thus, regionalization of CO₂ emissions by WTD only will remain uncertain. WTD dynamics explained some of the differences between peatlands as sites which became very dry during summer showed lower emissions. We introduced the aerated nitrogen stock (N_air) as a variable combining soil nitrogen stocks with WTD. CO₂ increased with N_air across peatlands. Soils with comparatively low SOC concentrations showed as high CO₂ emissions as true peat soils because N_air was similar. N₂O emissions were controlled by the WTD dynamics and the nitrogen content of the topsoil. CH₄ emissions can be well described by WTD and ponding duration during summer. Our results can help both to improve GHG emission reporting and to prioritize and plan emission reduction measures for peat and similar soils at different scales.     

Emissions of CO<Subscript>2</Subscript>, CH<Subscript>4</Subscript> and N<Subscript>2</Subscript>O from undisturbed,drained and mined peatlands in Estonia

The aim of this study is to estimate emissions of greenhouse gases CO₂, CH₄ and N₂O, and the effects of drainage and peat extraction on these processes, in Estonian transitional fens and ombrotrophic bogs. Closed-chamber-based sampling lasted from January to December 2009 in nine peatlands in Estonia, covering areas with different land-use practices: natural (four study sites), drained (six sites), abandoned peat mining (five sites) and active peat mining areas (five sites). Median values of soil CO₂ efflux were 1,509, 1,921, 2,845 and 1,741 kg CO₂-C ha^?1 year^?1 from natural, drained, abandoned and active mining areas, respectively. Emission of CH₄-C (median values) was 85.2, 23.7, 0.07 and 0.12 kg ha^?1 year^?1, and N₂O-N ?0.05, ?0.01, 0.18 and 0.19 kg ha^?1 year^?1, respectively. There were significantly higher emissions of CO₂ and N₂O from abandoned and active peat mining areas, whereas CH₄ emissions were significantly higher in natural and drained areas. Significant Spearman rank correlation was found between soil temperature and CO₂ flux at all sites, and CH₄ flux with high water level at natural and drained areas. Significant increase in CH₄ flux was detected for groundwater levels above 30 cm.     

Drainage-induced forest growth alters belowground carbon biogeochemistry in the Mer Bleue bog, Canada

Impacts of long-term drying and associated vegetation change on anaerobic decomposition, methane production, and pore water composition in peat bogs are poorly documented. To identify some of these impacts, we analyzed peat humification, pore water solutes, in situ and in vitro respiration rates, and Gibbs free energies of methanogenesis in a bog near a drainage ditch established in 1923. We compared drained peat under open bog vegetation and forest with a bog reference site. Drainage and tree growth induced an enrichment in carboxylic, aromatic, and phenolic moieties in the peat. Short-term in vitro respiration rates significantly decreased with humification (R ²?>?0.6, p?<?0.01). Dissolved inorganic carbon (DIC) and CH₄ concentrations also attained lower maxima in drained areas. However, near the water table in situ respiration intensified as indicated by steeper increases in DIC and CH₄ concentrations than at the reference site, especially under forest. Maximum in situ CO₂ production derived from inverse pore water modeling was 10.3?nmol?cm^?3?d^?1 (forest) and 6.3?nmol?cm^-3?d^-1 (bog) and was one to two orders of magnitude slower than in vitro anaerobic respiration. In the highly decomposed shallow peats under forest, methane production was suppressed and DOC concentration elevated. Raised H₂ concentrations (up to 200?nmol?l^?1) and in situ Gibbs free energies of down to ?60?kJ?mol^?1?(CH₄) suggested an inhibition of hydrogenotrophic methanogenesis by an unidentified factor at these sites. The study documents that several changes in biogeochemical process patterns do occur post-drainage, especially when tree growth is triggered. Most importantly, the establishment of forest on intensely humified peats can lower in situ methane production.     

Influence of weather variables on methane and carbon dioxide flux from a shallow pond

Freshwaters are important sources of the greenhouse gases methane (CH₄) and carbon dioxide (CO₂) to the atmosphere. Knowledge about temporal variability in these fluxes is very limited, yet critical for proper study design and evaluating flux data. Further, to understand the reasons for the variability and allow predictive modeling, the temporal variability has to be related to relevant environmental variables. Here we analyzed the effect of weather variables on CH₄ and CO₂ flux from a small shallow pond during a period of 4 months. Mean CH₄ flux and surface water CH₄ concentration were 8.0 [3.3–15.1] ± 3.1 mmol m^?2 day^?1 (mean [range] ± 1 SD) and 1.3 [0.3–3.5] ± 0.9 µM respectively. Mean CO₂ flux was 1.1 [?9.8 to 16.0] ± 6.9 mmol m^?2 day^?1. Substantial diel changes in CO₂ flux and surface water CH₄ concentration were observed during detailed measurements over a 24 h cycle. Thus diel patterns need to be accounted for in future measurements. Significant positive correlations of CH₄ emissions with temperature were found and could include both direct temperature effects as well as indirect effects (e.g. related to the growth season and macrophyte primary productivity providing organic substrates). CO₂ flux on the other hand was negatively correlated to temperature and solar radiation, presumably because CO₂ consumption by plants was higher relative to CO₂ production by respiration during warm sunny days. Interestingly, CH₄ fluxes were comparable to ponds with similar morphometry and macrophyte abundance in the tropics. We therefore hypothesize that CH₄ and CO₂ summer emissions from ponds could be more related to the morphometry and dominating primary producers rather than latitude per se. Data indicate that CH₄ emissions, given the system characteristic frameworks, is positively affected by increased temperatures or prolonged growth seasons.     

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.     

Release of CO2 and CH4 from lakes and drainage ditches in temperate wetlands

Shallow fresh water bodies in peat areas are important contributors to greenhouse gas fluxes to the atmosphere. In this study we determined the magnitude of CH₄ and CO₂ fluxes from 12 water bodies in Dutch wetlands during the summer season and studied the factors that might regulate emissions of CH₄ and CO₂ from these lakes and ditches. The lakes and ditches acted as CO₂ and CH₄ sources of emissions to the atmosphere; the fluxes from the ditches were significantly larger than the fluxes from the lakes. The mean greenhouse gas flux from ditches and lakes amounted to 129.1 ± 8.2 (mean ± SE) and 61.5 ± 7.1 mg m^?2 h^?1 for CO₂ and 33.7 ± 9.3 and 3.9 ± 1.6 mg m^?2 h^?1 for CH₄, respectively. In most water bodies CH₄ was the dominant greenhouse gas in terms of warming potential. Trophic status of the water and the sediment was an important factor regulating emissions. By using multiple linear regression 87% of the variation in CH₄ could be explained by PO₄ ^3? concentration in the sediment and Fe²⁺ concentration in the water, and 89% of the CO₂ flux could be explained by depth, EC and pH of the water. Decreasing the nutrient loads and input of organic substrates to ditches and lakes by for example reducing application of fertilizers and manure within the catchments and decreasing upward seepage of nutrient rich water from the surrounding area will likely reduce summer emissions of CO₂ and CH₄ from these water bodies.     

Carbon turnover in peatland mesocosms exposed to different water table levels

Changes of water table position influence carbon cycling in peatlands, but effects on the sources and sinks of carbon are difficult to isolate and quantify in field investigations due to seasonal dynamics and covariance of variables. We thus investigated carbon fluxes and dissolved carbon production in peatland mesocosms from two acidic and oligotrophic peatlands under steady state conditions at two different water table positions. Exchange rates and CO₂, CH₄ and DOC production rates were simultaneously determined in the peat from diffusive-advective mass-balances of dissolved CO₂, CH₄ and DOC in the pore water. Incubation experiments were used to quantify potential CO₂, CH₄, and DOC production rates. The carbon turnover in the saturated peat was dominated by the production of DOC (10–15 mmol m^–2 d^–1) with lower rates of DIC (6.1–8.5 mmol m^–2 d^–1) and CH₄ (2.2–4.2 mmol m^–2 d^–1) production. All production rates strongly decreased with depth indicating the importance of fresh plant tissue for dissolved C release. A lower water table decreased area based rates of photosynthesis (24–42%), CH₄ production (factor 2.5–3.5) and emission, increased rates of soil respiration and microbial biomass C, and did not change DOC release. Due to the changes in process rates the C net balance of the mesocosms shifted by 36 mmol m^–2 d^–1. According to our estimates the change in C mineralization contributed most to this change. Anaerobic rates of CO₂ production rates deeper in the peat increased significantly by a factor of 2–3.5 (DOC), 2.9–3.9 (CO₂), and 3–14 (CH₄) when the water table was lowered by 30 cm. This phenomenon might have been caused by easing an inhibiting effect by the accumulation of CO₂ and CH₄ when the water table was at the moss surface.     

The Effects of Infrared Loading and Water Table on Soil Energy Fluxes in Northern Peatlands

Increased radiative forcing is an inevitable part of global climate change, yet little is known of its potential effects on the energy fluxes in natural ecosystems. To simulate the conditions of global warming, we exposed peat monoliths (depth, 0.6 m; surface area, 2.1 m²) from a bog and fen in northern Minnesota, USA, to three infrared (IR) loading (ambient, +45, and +90 W m^–2) and three water table (–16, –20, and –29 cm in bog and –1, –10 and –18 cm in fen) treatments, each replicated in three mesocosm plots. Net radiation (Rn) and soil energy fluxes at the top, bottom, and sides of the mesocosms were measured in 1999, 5 years after the treatments had begun. Soil heat flux (G) increased proportionately with IR loading, comprising about 3%–8% of Rn. In the fen, the effect of IR loading on G was modulated by water table depth, whereas in the bog it was not. Energy dissipation from the mesocosms occurred mainly via vertical exchange with air, as well as with deeper soil layers through the bottom of the mesocosms, whereas lateral fluxes were 10–20-fold smaller and independent of IR loading and water table depth. The exchange with deeper soil layers was sensitive to water table depth, in contrast to G, which responded primarily to IR loading. The qualitative responses in the bog and fen were similar, but the fen displayed wider seasonal variation and greater extremes in soil energy fluxes. The differences of G in the bog and fen are attributed to differences in the reflectance in the long waveband as a function of vegetation type, whereas the differences in soil heat storage may also depend on different soil properties and different water table depth at comparable treatments. These data suggest that the ecosystem-dependent controls over soil energy fluxes may provide an important constraint on biotic response to climate change.     

A Multi-Year Record of Methane Flux at the Mer Bleue Bog,Southern Canada

The Mer Bleue peatland is a large ombrotrophic bog with hummock-lawn microtopography, poor fen sections and beaver ponds at the margin. Average growing-season (May–October) fluxes of methane (CH₄) measured in 2002–2003 across the bog ranged from less than 5 mg m⁻² d⁻¹ in hummocks, to greater than 100 mg m⁻² d⁻¹ in lawns and ponds. The average position of the water table explained about half of the variation in the season average CH₄ fluxes, similar to that observed in many other peatlands in Canada and elsewhere. The flux varied most when the water table position ranged between −15 and −40 cm. To better establish the factors that influence this variability, we measured CH₄ flux at approximately weekly intervals from May to November for 5 years (2004–2008) at 12 collars representing the water table and vegetation variations typical of the peatland. Over the snow-free season, peat temperature is the dominant correlate and the difference among the collars’ seasonal average CH₄ flux is partially dependent on water table position. A third important correlate on CH₄ flux is vegetation, particularly the presence of Eriophorum vaginatum, which increases CH₄ flux, as well as differences in the potential of the peat profile to produce and consume CH₄ under anaerobic and aerobic conditions. The combination of peat temperature and water table position with vegetation cover was able to explain approximately 44% of the variation in daily CH₄ flux, based on 1097 individual measurements. There was considerable inter-annual variation in fluxes, associated with varying peat thermal and water table regimes in response to variations in weather, but also by variations in the water level in peripheral ponds, associated with beaver dam activity. Raised water level in the beaver ponds led to higher water tables and increased CH₄ emission in the peatland.     

Winter CO2 CH4 and N2O fluxes on some natural and drained boreal peatlands

CO₂ and CH₄ fluxes during the winter were measured at natural and drained bog and fen sites in eastern Finland using both the closed chamber method and calculations of gas diffusion along a concentration gradient through the snowpack. The snow diffusion results were compared with those obtained by chamber, but the winter flux estimates were derived from chamber data only. CH₄ emissions from a poor bog were lower than those from an oligotrophic fen, while both CO₂ and CH₄ fluxes were higher in theCarex rostrata- occupied marginal (lagg) area of the fen than in the slightly less fertile centre. Average estimated winter CO₂-C losses from virgin and drained forested peatlands were 41 and 68 g CO₂-C m^–2, respectively, accounting for 23 and 21% of the annual total CO₂ release from the peat. The mean release of CH₄-C was 1.0 g in natural bogs and 3.4 g m^–2 in fens, giving rise to winter emissions averaging to 22% of the annual emission from the bogs and 10% of that from the fens. These wintertime carbon gas losses in Finnish natural peatlands were even greater than reported average long-term annual C accumulation values (less than 25g C m^–2). The narrow range of 10–30% of the proportion of winter CO₂ and CH₄ emissions from annual emissions found in Finnish peatlands suggest that a wider generalization in the boreal zone is possible. Drained forested bogs emitted 0.3 g CH₄-C m^–2 on the average, while the effectively drained fens consumed an average of 0.01 g CH₄-C m^–2. Reason for the low CH₄. efflux or net oxidation in drained peatlands probably lies in low substrate supply and thus low CH₄ production in the anoxic deep peat layers. N₂O release from a fertilized grassland site in November–May was 0.7 g N₂O m^–2, accounting for 38% of the total annual emission, while a forested bog released none and two efficiently drained forested fens 0.09 (28% of annual release) and 0.04 g N₂O m^–2 (27%) during the winter, respectively.     

Beryllium-7 as a natural tracer for short-term downwash in peat

Several factors can affect the integrity of natural archives such as peat records, e.g., decomposition and nutrient cycling, and it has also been hypothesized that some rapid downward transport of atmospherically derived elements may occur. We test this hypothesis by analyzing the short-lived, natural tracer beryllium-7 (t½ = 53.4 days) in five cores from two peatlands. In triplicate hummock cores from a raised bog in southern Sweden, ⁷Be could be measured to 20, 18 and 8 cm depth, and in a nutrient-poor mire in northern Sweden to a depth of 16 cm in a Sphagnum lawn core, but only 4 cm in the dominant, more-decomposed fen peat, indicating some spatial variability both within and between sites. Total ⁷Be inventories were 320–450 Bq m^?2 in the bog, and 150 Bq m^?2 (lawn) and 240 Bq m^?2 (fen peat) in the mire. 25–79 % of the total inventory of ⁷Be was located in the upper 2-cm layer. To further test downwashing, in the laboratory we applied a CuBr-solution to two cores and a Cu-solution to one core taken from the mire Sphagnum lawn, all with low water table conditions. About 50 % of the added Cu and ~35 % of the added Br were retained in the surface (2 cm) layer; 1–3 % of the Cu was found at 8–12 cm depth and ~1 % of the Br was measured in the lowest level (20–22 cm). Based on our novel approach using ⁷Be and experimental work we show that short-term downwashing can occur in peatlands and we suggest the depth of this will depend on the properties of the peat, e.g., bulk density and decomposition, as well as hydrology.     

Partitioning pathways of CO2 production in peatlands with stable carbon isotopes

Although methanogenic pathways generally produce equimolar amounts of carbon dioxide and methane, CO₂ concentrations are often reported to be higher than CH₄ concentrations in both field and laboratory incubation studies of peat decomposition. In field settings, higher pore water concentrations of CO₂ may result from the loss of methane by: (1) ebullition due to the low solubility of methane in pore water and (2) vascular-plant transport. Higher CO₂ concentrations may also be caused by: (1) production of additional CO₂ by high-molecular weight (HMW) organic matter (OM) fermentation and/or (2) respiration from non-methanogenic pathways. In this study of a peatland where advection and transverse dispersion were the dominant pore water solute transport mechanisms, an isotope-mass balance approach was used to determine the proportions of CO₂ formed from non-fractionating OM respiration and HMW fermentation relative to CO₂ production from methanogenesis. This approach also allowed us to estimate the loss of CH₄ from the belowground system. The pathways of CO₂ production varied with depth and surface vegetation type. In a Carex-dominated fen, methane production initially produced 40 % of the total CO₂ and then increased to 90–100 % with increasing depth. In a Sphagnum-dominated bog, methanogenesis resulted in 60 % of total CO₂ production which increased to 100 % at depth. Both bogs and fens showed 85–100 % of methane loss from pore waters. Our results indicate that the isotopic composition of dissolved CO₂ is a powerful indicator to allow partitioning of the processes affecting peat remineralization and methane production.