Subarctic Peatlands Research Articles

Climatic warming increases isoprene emission from a subarctic heath

Emissions of isoprene, a reactive hydrocarbon, from Subarctic vegetation are not well documented. However, the Arctic is likely to experience the most pronounced effects of climatic warming, which may increase temperature-dependent isoprene emission. Here, we assessed isoprene emission from a Subarctic heath subjected to a 3-4 degrees C increase in air temperature and mountain birch (Betula pubescens ssp. czerepanovii) litter addition for 7-8 yr, simulating climatic warming and the subsequent expansion of deciduous shrub species and migration of the treeline. The measurements were performed using the dynamic chamber method on a wet heath with a mixture of shrubs, herbs and graminoids. Isoprene emissions averaged across the treatments were 36 +/- 5 microg m(-2) h(-1) in 2006 and 58 +/- 7 microg m(-2) h(-1) in 2007. The experimental warming increased the emissions by 83% in 2007 (P = 0.021) and by 56% in 2006 (P = 0.056), while litter addition had no significant effects. The net ecosystem CO(2) exchange was significantly decreased by warming in 2007. These results show that isoprene emissions from Subarctic heaths are comparable to those from Subarctic peatlands. Climatic warming will increase the emissions, and the amount of carbon lost as isoprene, from Subarctic heath ecosystems.

Peatlands and the carbon cycle: from local processes to global implications – a synthesis

Abstract. Peatlands cover only 3% of the Earth's land surface but boreal and subarctic peatlands store about 15–30% of the world's soil carbon (C) as peat. Despite their potential for large positive feedbacks to the climate system through sequestration and emission of greenhouse gases, peatlands are not explicitly included in global climate models and therefore in predictions of future climate change. In April 2007 a symposium was held in Wageningen, the Netherlands, to advance our understanding of peatland C cycling. This paper synthesizes the main findings of the symposium, focusing on (i) small-scale processes, (ii) C fluxes at the landscape scale, and (iii) peatlands in the context of climate change. The main drivers controlling C fluxes are largely scale dependent and most are related to some aspects of hydrology. Despite high spatial and annual variability in Net Ecosystem Exchange (NEE), the differences in cumulative annual NEE are more a function of broad scale geographic location and physical setting than internal factors, suggesting the existence of strong feedbacks. In contrast, trace gas emissions seem mainly controlled by local factors. Key uncertainties remain concerning the existence of perturbation thresholds, the relative strengths of the CO2 and CH4 feedback, the links among peatland surface climate, hydrology, ecosystem structure and function, and trace gas biogeochemistry as well as the similarity of process rates across peatland types and climatic zones. Progress on these research areas can only be realized by stronger co-operation between disciplines that address different spatial and temporal scales.

Non-methane volatile organic compound flux from a subarctic mire in Northern Sweden

Biogenic NMVOCs are mainly formed by plants and microorganisms. They have strong impact on the local atmospheric chemistry when emitted to the atmosphere. The objective of this study was to determine if there are significant emissions of non-methane volatile organic compounds (NMVOCs) from a subarctic mire in northern Sweden. Subarctic peatlands in discontinuous permafrost regions are undergoing substantial environmental changes due to their high sensitivity to climate warming and there is need for includingNMVOCs in the overall carbon budget. Automatic and manual chamber measurements were used to estimateNMVOCfluxes from three dominating subhabitats on the mire during three growing seasons. Emission rates varied and were related to plant species distribution and seasonal net ecosystem exchange of carbon dioxide. The highest fluxes were observed from wetter sites dominated by Eriophorum and Sphagnum spp. Total NMVOC emissions from the mire (∼17 ha) is estimated to consist of ∼150 kgC during a growing season with 150 d. NMVOC fluxes can account for ∼5% of total net carbon exchange (−3177 kgC) at the mire during the same period. NMVOC emissions are therefore a significant component in a local carbon budget for peatlands

Accumulation of organic carbon over the past 150 years in five freshwater peatlands in western and central Europe

Under predicted scenarios of global climate change, peatlands may become a net source of greenhouse gases which will accelerate warming of the atmosphere. Comparative studies of peat bogs along present climatic gradients may provide an insight into the future response of boreal and subarctic peatlands to changing temperature and moisture. Three maritime peat bogs in the British Isles, and two high-elevation peatlands in the Czech Republic were studied. All sites were relatively wet, the mean annual temperatures were higher by up to 6 °C at the British/Irish sites than at the Czech sites. Cumulative carbon content in 210Pb-dated Sphagnum-dominated vertical peat cores increased from the warmer to the colder sites when evaluated for the most recent decades (since ca. 1950). That would correspond to formation of thinner, more highly decomposed peat deposits over the long-term in warmer conditions, and deeper peat bogs in colder conditions. However, when cumulative carbon content was evaluated for the last ca. 150 years, no relationship was found between mean annual temperature and the carbon pool size. Even along broad present-day climatic gradients, site-specific factors controlled organic carbon preservation in peat. Pollen analysis was instrumental in corroborating the 210Pb dates, identifying wet and dry periods in the past, and it also provided evidence for increasing nitrogen loads in wetland areas.

Isoprene emission from a subarctic peatland under enhanced UV‐B radiation

Isoprene is a reactive hydrocarbon with an important role in atmospheric chemistry, and emissions from vegetation contribute to atmospheric carbon fluxes. The magnitude of isoprene emissions from arctic peatlands is not known, and it may be altered by increasing UV-B radiation. Isoprene emission was measured with the dynamic chamber method from a subarctic peatland under long-term enhancement of UV-B radiation targeted to correspond to a 20% loss in the stratospheric ozone layer. The site type of the peatland was a flark fen dominated by the moss Warnstorfia exannulata and sedges Eriophorum russeolum and Carex limosa. The relationship between species densities and the emission was also assessed. Isoprene emissions were significantly increased by enhanced UV-B radiation during the second (2004) and the fourth (2006) growing seasons under the UV-B exposure. Emissions were related to the density of E. russeolum. The dominant moss, W. exannulata, proved to emit small amounts of isoprene in a laboratory trial. Subarctic fens, even without Sphagnum moss, are a significant source of isoprene to the atmosphere, especially under periods of warm weather. Warming of the Arctic together with enhanced UV-B radiation may substantially increase the emissions.

Peatlands and the carbon cycle: From local processes to global implications

Boreal and subarctic peatlands cover about 3% of the Earth's land surface and store 15–30% of the world's soil carbon (200–400 petagrams) as peat. This large C pool, in addition to C in Arctic soils, lies at higher latitudes that are experiencing ongoing climate change. Tropical peatlands also contain large C reservoirs, the stability of which is threatened by ongoing land use change. In response to a call from PeatNet (a National Science Foundation‐supported research coordination network), Juul Limpens and Gabriela Schaepman‐Strub proposed a small workshop on peatland C cycling, an idea that morphed into a meeting with 180 participants from 18 countries,

Changing leaf litter feedbacks on plant production across contrasting sub-arctic peatland species and growth forms

Plant species and growth forms differ widely in litter chemistry, which affects decay and may have important consequences for plant growth via e.g. the release of nutrients and growth-inhibitory compounds. We investigated the overall short-term (9.5 months) and medium-term (21.5 months) feedback effects of leaf litter quality and quantity on plant production, and tested whether growth forms can be used to generalise differences among litter species. Leaf litter effects of 21 sub-arctic vascular peatland species on Poa alpina test plants changed clearly with time. Across all growth forms, litter initially reduced plant biomass compared with untreated plants, particularly litters with a high decomposition rate or low initial lignin/P ratio. In the second year, however, litter effects were neutral or positive, and related to initial litter N concentration (positive), C/N, polyphenol/N and polyphenol/P ratios (all negative), but not to decomposability. Differences in effect size among several litter species were large, while differences in response to increasing litter quantities were not significant or of similar magnitude to differences in response to three contrasting litter species. Growth forms did not differ in initial litter effects, but second-year plant production showed a trend (P<0.10) for differences in response to litters of different growth forms: evergreen shrubs<graminoids or deciduous shrubs<forbs. While long-persisting negative litter effects were predominant across all growth forms, our data indicate that even within nutrient-constrained ecosystems such as northern peatlands, vascular plant species, and possibly growth forms, differ in litter feedbacks to plant growth. Differences in the composition of undisturbed plant communities or species shifts induced by external disturbance, such as climate change, may therefore feedback strongly to plant biomass production and probably nutrient cycling rates in northern peatlands.

Climate change has only a minor impact on nutrient resorption parameters in a high-latitude peatland

Nutrient resorption from senescing plant tissues is an important determinant of the fitness of plant populations in nutrient-poor ecosystems, because it makes plants less dependent on current nutrient uptake. Moreover, it can have significant "afterlife" effects through its impact on litter chemistry and litter decomposability. Little is known about the effects of climate change on nutrient resorption. We studied the effects of climate change treatments (including winter snow addition, and spring and/or summer warming) on nutrient resorption of four dominant species in a nutrient-poor subarctic peatland. These species were Betula nana (woody deciduous), Vaccinium uliginosum (woody deciduous), Calamagrostis lapponica (graminoid) and Rubus chamaemorus (forb). After five years of treatments both mature and senesced leaf N concentrations showed a small but significant overall reduction in response to the climate treatments. However, the effects were species-specific. For example, in the controls the N concentration in senesced leaves of Calamagrostis (3.0+/-0.2 mg N g(-1)) was about four times lower than for Rubus (11.2+/-0.2 mg N g(-1)). There were no significant treatment effects on N resorption efficiency (% of the N pool in mature leaves that is resorbed during senescence). The nitrogen resorption efficiency of Calamagrostis (about 80%) was higher than in the other three species (about 60%). Thus, climate change has only a minor impact on nutrient resorption parameters. However, given the substantial interspecific differences in these parameters, substantial changes in plant-soil feedbacks may be expected as a result of the observed changes in the species composition of high-latitude vegetation. These changes are species-specific and thus difficult to predict.

Reconstruction of changes in vegetation and trophic conditions of a palsa in a permafrost peatland, subarctic Québec, Canada

:Macrofossil and chronostratigraphic data of a peat monolith extracted from a palsa within a subarctic permafrost peatland were used to reconstruct changes in vegetation and trophic conditions of the study site during the last 4500 cal y BP. The vegetation cover developed from Carex marsh or wet meadow to poor fen, bog, and to palsa peatland communities. The ombrotrophication was favoured by late-Holocene cooling and by the high peat accumulation. Permafrost inception began about 1660-1630 calibrated y BP, at the end of the Sphagnum accumulation stage. A comparison of the late-Holocene development of two peatlands in the same region (Arlen-Pouliot & Bhiry, 2005, and this study) suggests that permafrost initiation was due to a cool, dry climate associated with the Little Ice Age. However, Sphagnum cover prevented the permafrost from melting.

Accelerated thawing of subarctic peatland permafrost over the last 50 years

In this study we provide a quantification of the main patterns of change of a subarctic peatland caused by permafrost decay monitored between 1957 and 2003. Up‐thrusting of the peatland surface due to permafrost aggradation during the Little Ice Age resulted in the formation of an extensive peat plateau that gradually fragmented into residual palsas from the 19th century to the present. Only about 18% of the original surface occupied by permafrost was thawed in 1957, whereas only 13% was still surviving in 2003. Rapid permafrost melting over the last 50 years caused the concurrent formation of thermokarst ponds and fen‐bog vegetation with rapid peat accumulation through natural successional processes of terrestrialization. The main climatic driver for accelerated permafrost thawing was snow precipitation which increased from 1957 to present while annual and seasonal temperatures remained relatively stable until about the mid‐1990s when annual temperature rose well above the mean. Contrary to current expectations, the melting of permafrost caused by recent climate change does not transform the peatland to a carbon‐source ecosystem as rapid terrestrialization exacerbates carbon‐sink conditions and tends to balance the local carbon budget.

The timing of snow melt controls the annual CO2 balance in a subarctic fen

The first continuous multi‐year measurements of the CO2 exchange between a subarctic fen and the atmosphere were conducted at Kaamanen in northern Finland (69°N). According to our six‐year data‐set, the fen is presently a sink of atmospheric CO2 with a mean rate of −22 g C m−2 yr−1. The interannual variation of the CO2 balances originates almost completely from the variations during the snow‐free period, but the efflux in the wintertime constitutes a significant part of the annual balance. The snow melt timing is the most important single determinant of the annual carbon balance. In contrast to a commonly‐held view, the hydrometeorological conditions during the growing season had only a minor effect on the annual balance, emphasizing the importance of year‐round measurements. This study indicates that climate warming may increase the length of the growing season and thus benefit rather than threaten the carbon pool of subarctic peatlands.

Responses of two Sphagnum moss species and Eriophorum vaginatum to enhanced UV-B in a summer of low UV intensity.

• The flux of ultraviolet (UV)-B radiation to the Earth's surface is increasing, particularly in high latitudes. We studied the sensitivity of some dominant plant species of boreal and subarctic peatlands to this increase. • Intact peat monoliths with the mosses Sphagnum balticum and Sphagnum papillosum, and cotton grass (Eriophorum vaginatum) were exposed to ambient solar UV-B or ambient solar UV-B supplemented by 30% in a field experiment in central Finland. • Although the UV-B dose was low during the growing season, owing to frequent cloudiness, both Sphagnum species showed significantly higher membrane permeability under enhanced UV-B. In S. balticum, UV-B tended to decrease the capitulum dry mass and induced a 30-40% increase in the concentration of chlorophyll and carotenoid pigments. Enhanced UV-B had no effects on leaf morphology, chlorophyll fluorescence or stomatal functioning in E. vaginatum. • The various UV-B responses in the Sphagnum species under investigation indicate that they may be sensitive even to small increases in solar UV-B radiation. By contrast, E. vaginatum appeared to tolerate the UV-B fluxes of the experiment.

Vascular plants as regulators of methane emissions from a subarctic mire ecosystem

Vascular plant functions as controlling mechanisms of methane emissions were investigated at two contrasting habitat types at a subarctic peatland ecosystem in northern Sweden. One of the habitats was ombrotrophic (vegetation dominated byEriophorum vaginatumandCarex rotundata), while the other was minerotrophic (vegetation dominated byEriophorum angustifolium). Through shading manipulations we successfully reduced the gross photosynthetic rates of the vascular plant communities. At the ombrotrophic site a 25% reduction in gross photosynthesis lead to a concomitant 20% reduction in methane emission rates, indicating a strong substrate‐based coupling between the vascular plant community and the methanogenic populations. At the minerotrophic site, methane emission rates were unaffected, although plant photosynthesis was reduced by almost 50%. However, the methane emission rates at the minerotrophic site were significantly correlated with the number of vascular plants. We conclude that at the minerotrophic site the vegetation influences methane emission rates by facilitating methane transportation between the soil and the atmosphere, while at the ombrotrophic site the relationship between the vascular plant community and methane emissions is mediated by substrate‐based interactions regulated by plant photosynthetic activity.

Carbon dioxide and methane dynamics in a sub-Arctic peatland in northern Finland

We studied carbon dynamics on various surface parts of a highly patterned fen, typical in northern Finland, to examine the importance of different microsites to the areal carbon fluxes. The studies were carried out in June-September 1995 on a mesotrophic flark fen (an aapa mire) in Kaamanen (69°08?N, 27° 17?E). Wet flarks, moist lawns and dry strings accounted for 60%, 10% and 30% of the surface area, respectively. A static chamber technique was applied to measure the CH4 exchange, the instantaneous net ecosystem exchange (NEE, transparent chamber) and the ecosystem respiration (Rtot? opaque chamber) in several microsites. The static chamber results were compared with those obtained by the eddy covariance technique. The mean daytime areal net ecosystem CO2 exchange rate measurement in conditions where photosynthesis was light saturated (PAR>400 ?mol m-2 s-1) varied during the measurement period from ?59 mg CO2-C m?2h?1 (release) to 250 (uptake). The mean CH4 emission during the measuring period was 78 mg CH4-Cm?2 d?1 on the flarks, 68 mg on the lawn and 6.0 mg on the strings. The strings without shrubs (mainly Betula nana) were in general net sources of CO2, even during the middle of the growing season, whereas the lawns, flarks and also strings growing B. nana showed a daytime net uptake of CO2. Areally integrated chamber results showed lower CO2 and higher CH4 fluxes than predicted from the eddy covariance measurements.

Carbon dioxide and methane dynamics in a sub-Arctic peatland in northern Finland

We studied carbon dynamics on various surface parts of a highly patterned fen, typical in northern Finland, to examine the importance of different microsites to the areal carbon fluxes. The studies were carried out in June-September 1995 on a mesotrophic flark fen (an aapa mire) in Kaamanen (69°08?N, 27° 17?E). Wet flarks, moist lawns and dry strings accounted for 60%, 10% and 30% of the surface area, respectively. A static chamber technique was applied to measure the CH4 exchange, the instantaneous net ecosystem exchange (NEE, transparent chamber) and the ecosystem respiration (Rtot? opaque chamber) in several microsites. The static chamber results were compared with those obtained by the eddy covariance technique. The mean daytime areal net ecosystem CO2 exchange rate measurement in conditions where photosynthesis was light saturated (PAR>400 ?mol m-2 s-1) varied during the measurement period from ?59 mg CO2-C m?2h?1 (release) to 250 (uptake). The mean CH4 emission during the measuring period was 78 mg CH4-Cm?2 d?1 on the flarks, 68 mg on the lawn and 6.0 mg on the strings. The strings without shrubs (mainly Betula nana) were in general net sources of CO2, even during the middle of the growing season, whereas the lawns, flarks and also strings growing B. nana showed a daytime net uptake of CO2. Areally integrated chamber results showed lower CO2 and higher CH4 fluxes than predicted from the eddy covariance measurements.

Limited effect of increased atmospheric CO2concentration on ombrotrophic bog vegetation

Summary Boreal and subarctic peatlands contain 20–30% of the world’s soil organic carbon, and if growing, they constitute sinks for atmospheric CO2. We hypothesized that even in the nutrient‐poor bog environment, elevated CO2would stimulateSphagnumgrowth more than vascular plant growth, thereby improvingSphagnum’scompetitive strength and enhancing carbon (C) sequestration. Free‐air carbon dioxide enrichment (FACE) experiments took place on predominantly ombrotrophic peatbog‐lawns in Finland (FI), Sweden (SW), The Netherlands (NL), and Switzerland (CH). After 3 yr of treatment, increased CO2concentration (560 ppm on volume basis) had no significant effect onSphagnumor vascular plant biomass at either site. This research suggests that, just as with other nutrient‐poor ecosystems, increased atmospheric CO2concentrations will have a limited effect on bog ecosystems.

PAST, PRESENT, AND FUTURE PEATLAND CARBON BALANCE: AN EMPIRICAL MODEL BASED ON210Pb-DATED CORES

Boreal and subarctic peatlands today represent a large global carbon (C) reservoir. Existing models that describe organic matter accumulation in peatlands over thousands of years are inadequate for predicting short-term responses to changing climate. This paper develops a new, empirically based model that estimates net primary production (NPP) and depth-dependent decay rates (exponential decay k values) of near-surface peat. Application of the model to three sites in boreal Alberta indicates that today the sites are net sinks for atmospheric C at rates of 34–52 g C·m−2·yr−1. Even without climate change, within 80–160 years, these sites will attain steady-state conditions with no further net C accumulation. Climate change scenarios in which NPP or k values are allowed to change gradually and linearly (at 0.1% per year) affect net C sequestration. Any scenario of decreasing NPP or increasing k values results in the peatlands switching from net sinks to net sources of atmospheric C within the next 20–62 year...

Carbon dioxide exchange in a subarctic peatland ecosystem in northern Europe measured by the eddy covariance technique

Micrometeorological measurements of carbon dioxide and energy fluxes were made on a mesotrophic flark fen in northern Finland (69°08′N, 27°17′E). The measurements were conducted from August 15 to September 13, 1995, the period extending from the intense phase of the growing season through its decline. The objective was to assess the net CO2 balance on a daily basis during the crucial time of the fen turning from a net sink to a net source of CO2. A clear decline in the CO2 fluxes was observed due to the senescence of the vascular plants at the end of August. The hourly median of daytime fluxes decreased from −0.12 to −0.04 mg m−2 s−1 from August to September. The nighttime fluxes decreased simultaneously from 0.07 to 0.04 mg m−2 s−1. A simple photosynthetically active radiation (PAR) driven net ecosystem exchange model was used to patch up the time series for calculating the diurnal balances. The value of the model parameter of maximal gross photosynthetic uptake changed from −0.320 to −0.134 mg m−2 s−1 from August to September. The value of α (initial slope of net ecosystem exchange versus PAR) changed, correspondingly, from −0.888 to −0.480 μg μmol−1. The highest negative daily balances at the beginning of the period were about −2 g m−2 d−1. During the first days of September they rose to 3 g m−2 d−1, but decreased to 1 g m−2 d−1 at the end of the measurements.

The Utilization of Bryophytes in Bioclimatic Modeling: Present Distribution of Peatlands in the Mackenzie River Basin, Canada

The Utilization of Bryophytes in Bioclimatic Modeling: Present Distribution of Peatlands in the Mackenzie River Basin, Canada

The Utilization of Bryophytes in Bioclimatic Modeling: Predicted Northward Migration of Peatlands in the Mackenzie River Basin, Canada, as a Result of Global Warming

The Utilization of Bryophytes in Bioclimatic Modeling: Predicted Northward Migration of Peatlands in the Mackenzie River Basin, Canada, as a Result of Global Warming