Peatland Carbon Accumulation Research Articles

Carbon accumulation in a permafrost polygon peatland: steady long-term rates in spite of shifts between dry and wet conditions.

Ice-wedge polygon peatlands contain a substantial part of the carbon stored in permafrost soils. However, little is known about their long-term carbon accumulation rates (CAR) in relation to shifts in vegetation and climate. We collected four peat profiles from one single polygon in NE Yakutia and cut them into contiguous 0.5 cm slices. Pollen density interpolation between AMS (14)C dated levels provided the time span contained in each of the sample slices, which--in combination with the volumetric carbon content--allowed for the reconstruction of CAR over decadal and centennial timescales. Vegetation representing dry palaeo-ridges and wet depressions was reconstructed with detailed micro- and macrofossil analysis. We found repeated shifts between wet and dry conditions during the past millennium. Dry ridges with associated permafrost growth originated during phases of (relatively) warm summer temperature and collapsed during relatively cold phases, illustrating the important role of vegetation and peat as intermediaries between ambient air temperature and the permafrost. The average long-term CAR across the four profiles was 10.6 ± 5.5 g C m(-2) yr(-1). Time-weighted mean CAR did not differ significantly between wet depression and dry ridge/hummock phases (10.6 ± 5.2 g C m(-2) yr(-1) and 10.3 ± 5.7 g C m(-2) yr(-1), respectively). Although we observed increased CAR in relation to warm shifts, we also found changes in the opposite direction and the highest CAR actually occurred during the Little Ice Age. In fact, CAR rather seems to be governed by strong internal feedback mechanisms and has roughly remained stable on centennial time scales. The absence of significant differences in CAR between dry ridge and wet depression phases suggests that recent warming and associated expansion of shrubs will not affect long-term rates of carbon burial in ice-wedge polygon peatlands.

Impacts of climate and vegetation change on carbon accumulation in a south-central Alaskan peatland assessed with novel organic geochemical techniques

To constrain the effect of climate and peatland type on carbon accumulation, we reconstructed these parameters from a Holocene-length core of a Sphagnum-dominated peatland near Cordova, AK, USA. We determined peat type using a combination of peat texture and density, macrofossils, distributions of leaf-wax biomarkers, and soil pH reconstructions based on distributions of branched glycerol dialkyl glycerol tetraether lipids (brGDGTs). We produced an independent record of hydroclimate and temperature change using hydrogen isotope ratios of leaf-wax biomarkers and distributions of brGDGTs. Carbon accumulation rates were constrained with 14 AMS 14C dates from identified macrofossils and ash-free bulk density. In the early Holocene, the site was a shallow pond with evidence for emergent macrophytes, Sphagnum, and algae growing in a warm, moist climate. At 9.2 kyr (1 kyr = 1000 cal. yr BP), the site became a Sphagnum-dominated bog. Under mid-Holocene warm, evaporative climate conditions, the site became sedge-dominated. As climate cooled and effective precipitation increased, Sphagnum was able to gain dominance abruptly at ~3.5 kyr. Large changes in the vegetation assemblage and hydrology and climate are contemporaneous with significant changes in the rate of carbon accumulation. Carbon accumulated most rapidly when Sphagnum dominated and effective moisture was high and most slowly when sedges were dominant and conditions were warmer and drier. Estimates of future climate change indicate warmer, more evaporative conditions that, in the past, favored a sedge-dominated environment, suggesting that this peatland and those similar can contribute to a positive feedback to warming by transitioning to less efficient carbon sinks.

N2-fixation by methanotrophs sustains carbon and nitrogen accumulation in pristine peatlands

Symbiotic relationships between N2-fixing prokaryotes and their autotrophic hosts are essential in nitrogen (N)-limited ecosystems, yet the importance of this association in pristine boreal peatlands, which store 25 % of the world’s soil (C), has been overlooked. External inputs of N to bogs are predominantly atmospheric, and given that regions of boreal Canada anchor some of the lowest rates found globally (~1 kg N ha−1 year−1), biomass production is thought to be limited primarily by N. Despite historically low N deposition, we show that boreal bogs have accumulated approximately 12–25 times more N than can be explained by atmospheric inputs. Here we demonstrate high rates of biological N2-fixation in prokaryotes associated with Sphagnum mosses that can fully account for the missing input of N needed to sustain high rates of C sequestration. Additionally, N amendment experiments in the field did not increase Sphagnum production, indicating that mosses are not limited by N. Lastly, by examining the composition and abundance of N2-fixing prokaryotes by quantifying gene expression of 16S rRNA and nitrogenase-encoding nifH, we show that rates of N2-fixation are driven by the substantial contribution from methanotrophs, and not from cyanobacteria. We conclude biological N2-fixation drives high sequestration of C in pristine peatlands, and may play an important role in moderating fluxes of methane, one of the most important greenhouse gases produced in peatlands. Understanding the mechanistic controls on biological N2-fixation is crucial for assessing the fate of peatland carbon stocks under scenarios of climate change and enhanced anthropogenic N deposition.

Carbon accumulation of tropical peatlands over millennia: a modeling approach.

Tropical peatlands cover an estimated 440,000 km2 (~10% of global peatland area) and are significant in the global carbon cycle by storing about 40-90 Gt C in peat. Over the past several decades, tropical peatlands have experienced high rates of deforestation and conversion, which is often associated with lowering the water table and peat burning, releasing large amounts of carbon stored in peat to the atmosphere. We present the first model of long-term carbon accumulation in tropical peatlands by modifying the Holocene Peat Model (HPM), which has been successfully applied to northern temperate peatlands. Tropical HPM (HPMTrop) is a one-dimensional, nonlinear, dynamic model with a monthly time step that simulates peat mass remaining in annual peat cohorts over millennia as a balance between monthly vegetation inputs (litter) and monthly decomposition. Key model parameters were based on published data on vegetation characteristics, including net primary production partitioned into leaves, wood, and roots; and initial litter decomposition rates. HPMTrop outputs are generally consistent with field observations from Indonesia. Simulated long-term carbon accumulation rates for 11,000-year-old inland, and 5000-year-old coastal peatlands were about 0.3 and 0.59 Mg C ha(-1) yr(-1), and the resulting peat carbon stocks at the end of the 11,000-year and 5000-year simulations were 3300 and 2900 Mg C ha(-1), respectively. The simulated carbon loss caused by coastal peat swamp forest conversion into oil palm plantation with periodic burning was 1400 Mg C ha(-1) over 100 years, which is equivalent to ~2900 years of C accumulation in a hectare of coastal peatlands.

Holocene peatland initiation, lateral expansion, and carbon dynamics in the Zoige Basin of the eastern Tibetan Plateau

The Zoige Basin on the eastern Tibetan Plateau has the largest area of highland peatlands in China. However, the development history of these peatlands is still poorly understood. Understanding how these carbon-rich ecosystems responded to change in the Asian summer monsoons during the Holocene will provide insight into the peatland carbon accumulation processes under different climate boundary conditions. Here, we document the timing of initiation and expansion histories of these peatlands using 59 new basal peat ages across the Zoige Basin, with 29 ages for initiation analysis and 30 additional ages for lateral expansion analysis. Also, we synthesized basal ages from 26 sites and carbon accumulation records at four sites from previous studies in this region. The results show that the peatland initiation is widespread at 11.5–10 and 7–6 kyr (1 kyr = 1000 cal. yr BP) and the minimum initiation periods occurred after 5 kyr. Our multiple basal ages along eight transects show that slopes are a dominant control on peatland lateral expansion rates, with very slow and less variable rates at slopes >0.4°. Furthermore, we found a significant relationship between peatland basal ages and peat depths from 85 sites, suggesting relatively uniform peat properties. Carbon accumulation rates from detailed downcore analysis at four sites and on the basis of peat depth–basal age relationship show similar patterns with a peak carbon accumulation at 10–8 kyr. On the basis of estimated mean values of bulk density and carbon content from the region, the Holocene average C accumulation for the Zoige Basin is 31.1 g C/m2/yr. The widespread peatland initiation and rapid accumulation in the early Holocene were likely in response to higher temperature and stronger summer monsoon intensity, while the slowdown of peatland development during the late Holocene might have been caused by climate cooling and drying.

Surface vegetation patterning controls carbon accumulation in peatlands

AbstractLocalized ecohydrological feedbacks have been proposed as important internal drivers of patterns and processes in terrestrial ecosystems. However, there is a significant gap between the prominence of theoretical models and the paucity of observations describing linkages between ecosystem structure and functioning. Here we report empirical evidence for strong interactions between surface vegetation patterning and long‐term carbon sequestration rates in four peat bogs in Patagonia on the basis of high‐resolution stratigraphic analyses. Peatland development across the study region was characterized by repeated switches between wet‐ and dry‐adapted plant communities, depicting changes between hollows (wet assemblages) and lawns (dry assemblages) that could represent past surface patterning. We found a site‐specific relationship between the frequency of the wet‐to‐dry cycles and carbon accumulation rates that followed a power function, with rapid vegetation shifts causing high peat accumulation rates. Our results show strong evidence for internal regulation of vegetation dynamics and peatland growth, implying that understanding peatland processes is a prerequisite for peat‐based paleoclimate reconstructions.

Recent increase in peatland carbon accumulation in a thermokarst lake basin in southwestern Alaska

Drained thermokarst lake basins cover large areas of northern high latitude lowlands. However, the importance of peat accumulated in these drained basins to carbon (C) cycling is poorly understood. Results are presented here from a permafrost sediment core aimed at investigating site history, lake drainage, apparent carbon accumulation, and paleohydrology in a thermokarst basin on the Yukon Kuskokwim Delta in southwestern Alaska. The results show that a thermokarst lake existed for about 2300years before it drained and a peatland established in the early 1600s. Average apparent C accumulation rate (CAR) was 12gC/m2/yr over the 2300years before lake drainage, but increased to 120gC/m2/yr following peatland initiation. After transitioning to a Sphagnum-dominated peatland at ~1700AD, CAR reduced gradually before more than doubling from the mid-1970s to the early 1980s. This abrupt increase in CAR was possibly in response to a Pacific climate regime shift in the late 1970s, a transition characterized by a nearly 1.5°C increase in regional average annual temperature. Even after considering the differential decay of recent peat, there was an increase in C accumulation after 1977. Reconstructed water-table depths from subfossil testate amoebae show little change throughout the past three centuries, but there was a pronounced shift in testate amoeba composition after the 1977 temperature change (e.g., absence of Phryganella acropodia type and increase in Hyalosphenia elegans). If the results from peatlands in other drained thermokarst lake basins are consistent with the results from this study, then the C accumulated in these vegetated drained basins under current warming might help offset some of the C released from thawing permafrost and thermokarst features in northern regions.

The impact of high tephra loading on late-Holocene carbon accumulation and vegetation succession in peatland communities

Peatlands are major terrestrial stores of carbon (C) of importance to the global climate system. Recent studies have made progress in understanding the climatic controls on the C cycle; however, important interactions between volcanic deposition and peatland C stores remain to be addressed. This study uses a 3000-year peatland record from northern Japan to examine the interactions between carbon accumulation, vegetation community succession and volcanic ash deposition. Plant macrofossil and testate amoebae records are presented alongside records of total organic carbon, nitrogen and phosphorous. Age–depth models are developed using a Bayesian approach, with seven AMS radiocarbon dates and two identified historical tephras from Baitoushan (AD 969 (981 cal. BP)), and Hokkaido-Komagatake (AD 1640 (310 cal. BP)) volcanoes. Results show that moderate to high tephra loading can shift peatland plant communities from Sphagnum to monocotyledon domination. This vegetation change is associated with increased peat humification and reduced carbon accumulation. Where tephra deposition and reworking has occurred, the apparent rate of carbon accumulation can be halved while high tephra loading of the mire surface is sustained. Sphagnum species vary in their tolerance to tephra deposition. After each ash fall Sphagnum magellanicum disappeared from the plant macrofossil record, whereas Sphagnum papillosum showed apparent continuity of development through the 1856 (94 cal. BP) Ko-c1 tephra. High rates of carbon accumulation (peaking at >100 g m−2 yr−1), 2–3 times faster than the average for northern peatlands, were recorded in the Sphagnum communities that established after the cessation of tephra deposition and reworking from the AD 969 Baitoushan ash fall (B-Tm tephra). This peak in C accumulation was coincident with a radical shift in mire nutrient cycling most probably caused by the interaction of S. magellanicum with leachates from the underlying tephras. The phase of high C accumulation continued for over 300 years, offsetting the initial negative impact of the B-Tm tephra on peatland C accumulation. These results suggest that management for ash-tolerant Sphagnum species could be a highly effective strategy for minimising volcanic disruption to peatland carbon accumulation. The study also shows that consideration of volcanic impacts on peatlands is essential for development of more realistic terrestrial carbon balance models in volcanically active regions.

Sobol' sensitivity analysis of the Holocene Peat Model: What drives carbon accumulation in peatlands?

Understanding the development of northern peatlands and their carbon accumulation dynamics is crucial in order to confidently integrate northern peatlands into global carbon cycle models. To achieve this, northern peatland models are becoming increasingly complex and now include feedback processes between peat depth, decomposition, hydrology, and vegetation composition and productivity. Here we present results from a global sensitivity analysis performed to assess the behavior and parameter interaction of a peatland simulation model. A series of simulations of the Holocene Peat Model were performed with different parameter combinations in order to assess the role of parameter interactions on the simulated total carbon mass after 5000 years of peatland development. The impact of parameter uncertainty on the simulation results is highlighted, as is the importance of multiple parameter interactions. The model sensitivity indicates that peat physical properties play an important role in peat accumulation; these parameters are poorly constrained by observations and should be a focus of future research. Furthermore, the results show that autogenic processes are able to produce a wide range of peatland development behaviors independently of any external environmental changes.

Climate-related changes in peatland carbon accumulation during the last millennium

Abstract. Peatlands are a major terrestrial carbon store and a persistent natural carbon sink during the Holocene, but there is considerable uncertainty over the fate of peatland carbon in a changing climate. It is generally assumed that higher temperatures will increase peat decay, causing a positive feedback to climate warming and contributing to the global positive carbon cycle feedback. Here we use a new extensive database of peat profiles across northern high latitudes to examine spatial and temporal patterns of carbon accumulation over the past millennium. Opposite to expectations, our results indicate a small negative carbon cycle feedback from past changes in the long-term accumulation rates of northern peatlands. Total carbon accumulated over the last 1000 yr is linearly related to contemporary growing season length and photosynthetically active radiation, suggesting that variability in net primary productivity is more important than decomposition in determining long-term carbon accumulation. Furthermore, northern peatland carbon sequestration rate declined over the climate transition from the Medieval Climate Anomaly (MCA) to the Little Ice Age (LIA), probably because of lower LIA temperatures combined with increased cloudiness suppressing net primary productivity. Other factors including changing moisture status, peatland distribution, fire, nitrogen deposition, permafrost thaw and methane emissions will also influence future peatland carbon cycle feedbacks, but our data suggest that the carbon sequestration rate could increase over many areas of northern peatlands in a warmer future.

Hydrology-mediated differential response of carbon accumulation to late Holocene climate change at two peatlands in Southcentral Alaska

Peatlands are among the largest reservoirs of terrestrial carbon in the northern hemisphere. Understanding how this reservoir will respond to climate changes is critical to assessing potential climate feedbacks. Peatland carbon accumulation rates (PCAR) are controlled by the difference between production and decomposition, which is affected by local and climatic factors including hydrology and temperature. To better understand how local controls can influence the response of PCAR to climate change, we investigated modern hydrology, paleohydrology, and PCAR at two nearby Sphagnum-dominated peatlands with different surficial geology (lowland and moraine settings) in Southcentral Alaska. Modern hydrological data indicated a higher rate of subsurface drainage at the lowland site, suggesting greater hydrologic sensitivity to prolonged dry periods of the past. We investigated past responses of these peatlands to well-documented climatic changes, like the Medieval Climate Anomaly (MCA) at ∼1000–600 cal yr BP and Little Ice Age (LIA) at ∼600–200 cal yr BP, using water-table depth (WTD) inferred from testate amoebae and PCAR calculated from loss-on-ignition and 14C-dating analyses. Our results indicate that WTD and PCAR remained relatively stable at the moraine site throughout the last 1100 years, including the MCA and LIA. However, the lowland site experienced relatively stable WTD and higher PCAR during the MCA, but highly variable WTD and lower PCAR during the LIA. These differences suggest that hydrology and likely decomposition were the primary control on PCAR at these peatlands. Our results highlight the importance of local-scale controls, like surficial geology, in mediating the response of peatland hydrology and carbon accumulation to climate change.

Northern peatland carbon accumulation and climate change during the last millennium

Northern peatland carbon accumulation and climate change during the last millennium

Quantifying spatial and temporal Holocene carbon accumulation in ombrotrophic peatlands of the Eastmain region, Quebec, Canada

[1] Northern peatlands represent important stocks of organic carbon (C). Peatland C dynamics have the potential to influence atmospheric greenhouse gas concentrations and are therefore of interest concerning future climate change. Quantification of Holocene variations in peat C accumulation rates is often based on a single, deep core. However, deep cores may overestimate accumulation rates when extrapolated to the ecosystem scale. We propose a reconstruction of C sequestration patterns based on multiple cores from three ombrotrophic peatlands in boreal Quebec, Canada. Both total C accumulation and temporal variations herein were quantified. Radiocarbon-dated stratigraphies from different sections resulted in peatland-specific age-depth models. Peatland initiation started rapidly after deglaciation around 7500 cal BP. Vertical accumulation slowed down in the course of the Holocene, whereas lateral expansion was rapid in the early stages but slowed down near mid-Holocene. Total C accumulation showed maximum rates between 5250 and 3500 cal BP with a regional mean Holocene apparent rate of 16.2 g m−2 yr−1. The Eastmain peatlands have been modest sinks of organic C compared to those of Alaska, western Canada, and western Siberia, although differences in calculation methods hamper direct comparisons. Considering within-peatland dynamics, maximum total C sequestration coincided with a period of slowing down in both lateral expansion and vertical accumulation. Late-Holocene diminishing peatland C sink functions have been attributed to autogenic as well as allogenic factors. Height-induced surface drying and/or neoglacial cooling effects may have forced the slowing down of C sequestration in the studied bogs. Results further show that, in order to obtain an accurate quantification of past C sequestration, reconstructions of peatland expansion are essential.

Constraints on carbon accumulation rate and net primary production in the Lopingian (Late Permian) tropical peatland in SW China

During the Permian, peatland, as represented in extensive coal deposits, was a major component of the global carbon cycle. Carbon storage in peatland is a balance between decay and net primary production (NPP), which in turn are sensitive to variations in the concentration of atmospheric CO2 and O2. To evaluate peatland carbon storage and NPP during the Lopingian, a period thought to be characterised by higher atmospheric O2 and CO2 than modern levels, spectral analyses of geophysical data from a 15.1m thick Lopingian (Upper Permian) coal in southwestern China were conducted to define the time frame of temporal carbon accumulation in tropical peatland. The result shows that the mineral matter content (ash yield) of the coal was possibly influenced by 123ka (eccentricity), 35.6ka (obliquity) and 21.2ka (precession) Milankovitch periodicities. Using this timeframe and an understanding of carbon loss during coalification, the Lopingian tropical peatland carbon accumulation rate is calculated to be 61.1–73.0gC/m2/yr which is expected to correspond to a NPP of 611–1460gC/m2/yr respectively. A comparison between the predicted Pennsylvanian (Late Carboniferous) NPP and modern values indicates that the Permian NPP calculated is consistent with geochemical and paleobotanical models, supporting a proposal that productivity was mainly controlled by temporal atmospheric O2 and CO2 levels.

Carbon accumulation in peatlands of West Siberia over the last 2000 years

We use a network of cores from 77 peatland sites to determine controls on peat C content and peat C accumulation over the last 2000 years (since 2 ka) across Russia's West Siberian Lowland (WSL), the world's largest wetland region. Our results show a significant influence of fossil plant composition on peat C content, with peats dominated by Sphagnum having a lower C content. Radiocarbon‐derived C accumulation since 2 ka at 23 sites is highly variable from site to site, but displays a significant N–S trend of decreasing accumulation at higher latitudes. Northern WSL peatlands show relatively small C accumulation of 7 to 35 kg C m−2 since 2 ka. In contrast, peatlands south of 60°N show larger accumulation of 42 to 88 kg C m−2. Carbon accumulation since 2 ka varies significantly with modern mean annual air temperature, with maximum C accumulation found between −1 and 0°C. Rates of apparent C accumulation since 2 ka show no significant relationship to long‐term Holocene averages based on total C accumulation. A GIS‐based extrapolation of our site data suggests that a substantial amount (∼40%) of total WSL peat C has accumulated since 2 ka, with much of this accumulation south of 60°N. The large peatlands in the southern WSL may be an important component of the Eurasian terrestrial C sink, and future warming could result in a shift northward in long‐term WSL C sequestration.

Sphagnum under pressure: towards an ecohydrological approach to examining Sphagnum productivity

AbstractThe genus Sphagnum is the key peat‐forming bryophyte in boreal ecosystems. Relying entirely on passive capillary action for water transport, soil moisture is often the limiting factor in Sphagnum production, and hence peat accumulation. While several hydrological models of peat physics and peatland water movement exist, these models do not readily interface with observations and models of peatland carbon accumulation. A conflict of approaches exists, where hydrological studies primarily utilize variables such as hydraulic head, while ecological models of Sphagnum growth adopt the coarse hydrological variables of water table (WT), volumetric water content (VWC) or gravimetric water content (WC). This review examines the potential of soil pressure head as a measurement to link the hydrological and ecological functioning of Sphagnum in peatlands. The non‐vascular structure of Sphagnum mosses and the reliance on external capillary transport of water in the mosses make them an ideal candidate for this approach. The main advantage of pressure head is the ability to mechanistically link plot‐scale hydrology to cellular‐scale water requirements and carbon exchange. Measurement of pressure head may improve photosynthetic process representation in the next generation of peatland models. Copyright © 2008 John Wiley & Sons, Ltd.

A 1.16 Ma record of carbon accumulation in western European peatland during the Oligocene from the Ballymoney lignite, Northern Ireland

The Oligocene Ballymoney lignite in Northern Ireland is one of the thickest lignites in Europe and provides the potential for comparing Holocene and pre-Holocene peatland evolution and its response to long-term climate change on time scales much greater than 10 ka. Samples were collected from 50 m of lignite and analysed for δ 13 C. Spectral analysis of the δ 13 C record reveals that the record contains significant frequencies at 0.21 m −1 and 1.12 m −1 . These cycles are interpreted as the c . 100 ka eccentricity and 20 ka precession cycles, respectively. These cycles were then tuned and the duration was determined as 1.16 Ma with a carbon accumulation rate of 27 g C m −2 a −1 . If long-term changes in lignite δ 13 C are related to changes in the δ 13 C of the exogenic carbon reservoir, and if the lignite Chattian age is accepted, then the lignite probably formed between 24.6 and 25.8 Ma. Comparison of the estimated carbon accumulation rate with other Cenozoic peatland carbon accumulation rates indicates that this rate appears to be insensitive to changes in the concentration of atmospheric CO 2 .

Holocene radiative forcing impact of northern peatland carbon accumulation and methane emissions

AbstractThroughout the Holocene, northern peatlands have both accumulated carbon and emitted methane. Their impact on climate radiative forcing has been the net of cooling (persistent CO2uptake) and warming (persistent CH4emission). We evaluated this by developing very simple Holocene peatland carbon flux trajectories, and using these as inputs to a simple atmospheric perturbation model. Flux trajectories are based on estimates of contemporary CH4flux (15–50 Tg CH4 yr−1), total accumulated peat C (250–450 Pg C), and peatland initiation dates. The contemporary perturbations to the atmosphere due to northern peatlands are an increase of ∼100 ppbv CH4and a decrease of ∼35 ppmv CO2. The net radiative forcing impact northern peatlands is currently about −0.2 to −0.5 W m−2(a cooling). It is likely that peatlands initially caused a net warming of up to +0.1 W m−2, but have been causing an increasing net cooling for the past 8000–11 000 years. A series of sensitivity simulations indicate that the current radiative forcing impact is determined primarily by the magnitude of the contemporary methane flux and the magnitude of the total C accumulated as peat, and that radiative forcing dynamics during the Holocene depended on flux trajectory, but the overall pattern was similar in all cases.

Carbon accumulation in peatlands, southwestern Northwest Territories, Canada

Northern peatlands have stored significant quantities of carbon (C) since the early Holocene at rates that vary among peatland types. Pollen concentration dating was used to provide estimates o f true C accumulation and sequestration efficiency in different peatland systems in the discontinuous permafrost zone near Fort Simpson, Northwest Territories, Canada. The catotelm portions of bog, permafrost-affected peat plateau, and Sphagnum-dominated cores were interpreted to conform to Clymo’s (1984) model of C accumulation, while peat deposited under conditions with high water tables (rich fen and collapse fen) did not. The model assumes a consistent surface production, yet production in fens is thought to be highly sensitive to water table changes and may have contributed to poor model fits. Decay rates measured over the past 1200 yr range from 0.0015 to 0.0004 yr-1. True C accumulation rates (range 7.0 in peat plateau to 18.6 g C m-2 yr-1 in bog) and sequestration efficiencies (range 0.24 in peat plateau to 0.67 in poor fen) by 1200 yr BP were low in comparison with other North American sites. Decay rates measured over 1200 yr were significantly greater than that measured over the entire life span of the peatland (0.00033 yr-1), suggesting that a catotelm true C accumulation model incorporating a decreasing rate of decay would be more applicable. Key words: Carbon accumulation, peatlands, permafrost, northern Canada

Nitrogen deposition and increased carbon accumulation in ombrotrophic peatlands in eastern Canada

Recent and long‐term accumulation rates of carbon (C), using 210Pb‐ and 14C‐dating, were examined in 23 ombrotrophic peatlands in eastern Canada, where average 1990–1996 atmospheric wet nitrogen (N) deposition ranged from 0.3 to 0.8 g N m−2 yr−1. The average recent rate of C accumulation (RERCA) over the past 150 years was 73 ± 17 (SD) g C m−2 yr−1, ranging from 40 to 117 g C m−2 yr−1. The difference in RERCA between hummocks (78 g C m−2 yr−1) and hollows (65 g C m−2 yr−1) was significant. Increased RERCA over the past 50 years was found in hummocks and hollows in regions of higher N deposition and related to both elevated N deposition and growing degree‐days above +5°C. There was a statistically significant positive relationship between N deposition alone and present‐day C accumulation in both hummocks and hollows (R2 = 0.28 and 0.38, respectively). Recent N accumulation was significantly larger in high N deposition regions. The total average aboveground vegetation biomass of hollows and hummocks did not differ significantly with N deposition. However, a significantly larger vascular plant leaf biomass was found in both hollows and hummocks of the high N deposition class than in the low N deposition class (>0.6 and <0.4 g m−2 yr−1, respectively). The average long‐term apparent rate of C accumulation (LORCA) at 15 sites was 19 ± 8 (SD) g C m−2 yr−1, with no significant difference due to age of peat inception, latitude, or continentality.