Carbon Balance Of Peatlands Research Articles

Global-scale pattern of peatland <i>Sphagnum</i> growth driven by photosynthetically active radiation and growing season length

Abstract. High-latitude peatlands contain about one third of the world's soil organic carbon, most of which is derived from partly decomposed Sphagnum (peat moss) plants. We conducted a meta-analysis based on a global data set of Sphagnum growth measurements collected from published literature to investigate the effects of bioclimatic variables on Sphagnum growth. Analysis of variance and general linear models were used to relate Sphagnum magellanicum and S. fuscum growth rates to photosynthetically active radiation integrated over the growing season (PAR0) and a moisture index. We found that PAR0 was the main predictor of Sphagnum growth for the global data set, and effective moisture was only correlated with moss growth at continental sites. The strong correlation between Sphagnum growth and PAR0 suggests the existence of a global pattern of growth, with slow rates under cool climate and short growing seasons, highlighting the important role of growing season length in explaining peatland biomass production. Large-scale patterns of cloudiness during the growing season might also limit moss growth. Although considerable uncertainty remains over the carbon balance of peatlands under a changing climate, our results suggest that increasing PAR0 as a result of global warming and lengthening growing seasons, without major change in cloudiness, could promote Sphagnum growth. Assuming that production and decomposition have the same sensitivity to temperature, this enhanced growth could lead to greater peat-carbon sequestration, inducing a negative feedback to climate change.

In situ quantification of CH4 bubbling events from a peat soil using a new infrared laser spectrometer

CH4 emissions from peatlands are space and time dependent. The variety of efflux routes contributes to these variabilities. CH4 bubbling remains difficult to investigate since it occurs on a timescale of seconds. The aims of this study were to use for the first time the recently built infrared high-resolution spectrometer, SPectrometre Infra-Rouge In situ Tropospherique to (1) measure in situ CH4 fluxes in natural and artificial peatland plot and (2) observe online bubbling events with quantification of CH4 emission fluxes corresponding to this very sudden degassing event. The closed dynamic chamber method was used and the gas concentration was measured every 1.5 s. Emission fluxes were calculated by the accumulation rate of CH4 against time. Measurements were undertaken during daytime in March 2009 and during day- and nighttime in May 2009, in Sphagnum and Betula plots and in a wet artificially bared peat area with Eriophorum vaginatum. The results show that the CH4 emissions estimated with the SPectrometre Infra-Rouge In situ Tropospherique (SPIRIT) are consistent with those already published. The high emissions, both through diffusion and bubbling in the Eriophorum plot, were on the same order as the emissions estimated in natural shallow pools. During daytime, CH4 bubbling was higher in May (54.7% of the total emission) than in March (40.7%) probably because of increased CH4 production and accumulation in peat. In May, bubbling was higher at nighttime (65.5%) than in daytime (54.7%). This has an important implication for carbon budget assessment in peatlands. The recently built infrared spectrometer, SPIRIT, was able to reliably measure CH4 fluxes and quantify CH4 flux during the degassing of bubbles. The emissions obtained are in agreement with previously published data using other measurement techniques. The results of this preliminary work highlight (1) the importance of shallow pools in peatland CH4 emissions and (2) the sensitivity of such fluxes to atmospheric pressure, a relation that has not been fully investigated or taken into account in assessing peatland carbon balance.

Impact of gully erosion on carbon sequestration in blanket peatlands

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 45:31-41 (2010) - DOI: https://doi.org/10.3354/cr00887 Impact of gully erosion on carbon sequestration in blanket peatlands Martin Evans1,*, John Lindsay2 1Upland Environments Research Unit, School of Environment and Development, University of Manchester, Manchester M19 3PL, UK 2Department of Geography, University of Guelph, 50 Stone Road East, Guelph, Ontario N1G 2W1, Canada *Email: martin.evans@manchester.ac.uk ABSTRACT: Over 50% of UK soil carbon is stored in peatland systems and 75% of these peatlands are upland blanket bog. The upland blanket bogs of the UK have suffered severe erosion over the last millennium so that they are widely dissected by gully systems. Gully erosion entails primary removal of particulate carbon from the peatland system but also has secondary effects in that it enhances drainage and lowers water tables, potentially enhancing decomposition of surface peats. This paper exploits recent high resolution mapping of the gully erosion on the Bleaklow Plateau in the southern Pennines and existing data on peat growth rates in the area to assess the impact of gully erosion on peatland carbon balance and the relative importance of primary and secondary impacts of gullying on carbon sequestration. The results indicate that gully erosion during the last millennium has shifted the Bleaklow Plateau from being a net sink of carbon (–20.3 gC m–2 yr–1) to a net source (29.4 gC m–2 yr–1). The relative importance of gullying impacts can be expressed as follows: particulate organic carbon (POC) flux > change in gully net ecosystem exchange >> loss of gully margin carbon sequestration. The implication of these findings is that the magnitude of the potentially reversible impacts of gully erosion (reduced carbon fixation due to vegetation loss and ongoing erosional loss of POC) far exceed the effects associated with irreversible morphological change (enhanced peat decomposition in gully margin locations). KEY WORDS: Blanket peat · Gully erosion · Carbon balance · Carbon sequestration Full text in pdf format PreviousNextCite this article as: Evans M, Lindsay J (2010) Impact of gully erosion on carbon sequestration in blanket peatlands. Clim Res 45:31-41. https://doi.org/10.3354/cr00887 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 45. Online publication date: December 30, 2010 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2010 Inter-Research.

Geochemical controls on anaerobic organic matter decomposition in a northern peatland

The decomposition of deep peat deposits controls the long‐term carbon balance of peatlands but is poorly understood with respect to rates and controls. To rectify this deficiency, we estimated in situ dissolved inorganic carbon (DIC) and methane (CH4) production rates from a beaver pond to a central bog dome and related them to organic matter properties, Gibbs free energies of respiration, and δ13C values of DIC and CH4. DIC and CH4 production decreased from maxima of ~10 nmol cm‐3 d‐1 near the water table to values <0.1 nmol cm‐3 d‐1 at depths >1 m, and there was little differentiation among sites. Deeper into the peat, we measured an accumulation of DIC, CH4, and dissolved organic matter (DOM) enriched in aromatic and phenolic moieties, which resulted from the slowness of diffusive vertical pore‐water movement. Lack of transport may have slowed decomposition in two ways: (1) Aromatic and phenolic DOM moieties accumulated, while the release of carbohydrate‐rich DOM from peat was apparently impeded. (2) The accumulation of DIC and CH4 reduced Gibbs free energy of acetoclastic methanogenesis toward a critical threshold value of ‐25 to ‐20 kJ mol‐1 CH4. Hydrogenotrophic methanogenesis was energetically more favorable and generally dominated according to an isotopic fractionation between CO2 and CH4 of 1.053 to 1.076, but it was apparently impeded by some other factor. We conclude that lateral homogeneity and slowness of decomposition in geologically sealed deep peat deposits are assisted by a lack of solute transport, which facilitates the formation of deep peat deposits over millennia.

CO<sub>2</sub> exchange and carbon balance in two grassland sites on eutrophic drained peat soils

Abstract. In this study we investigated the role of intensive and extensive dairy farm practices on CO2 exchange and the carbon balance of peatlands by means of eddy covariance (EC) measurements. Year long EC measurements were made in two adjacent farm sites on peat soil in the western part of the Netherlands. One site (Stein) is a new meadow bird reserve and is managed predominantly by mowing in June and August. The second site (Oukoop) is an intensive dairy farm. Maximum photosynthetic uptake of the grass sward (range 2 to 34 μmol CO2 m−2 s−1) showed a close and similar linear relationship with Leaf Area Index (LAI; range 1 to 5) except in maturing hay meadows, where maximum photosynthetic uptake did not increase further. Apparent quantum yield varied between 0.02 and 0.08 (mean 0.045) μmol CO2 μmol−1 photons at both sites and was significantly correlated with LAI during the growth season. Ecosystem Respiration at 10°C (R10) calculated from the year round data set was 3.35 μmol CO2 m−2 s−1 at Stein and 3.69 μmol CO2 m−2 s−1 at Oukoop. Both sites were a source of carbon in winter and a sink during summer with net ecosystem exchange varying between 50 to 100 mmol CO2 m−2 d−1 in winter to below −400 mmol CO2 m−2 d−1 in summer. Periodically, both sites became a source after mowing. Net annual ecosystem exchange (NEE) for Stein was −5.7 g C m−2 a−1 and for Oukoop 133.9 g C m−2 a−1. When biomass removal, manure applications and estimates of methane emissions ware taken into account, both eutrophic peat meadows are a strong source for C around 420 g C m−2 a−1.

RESPONSE OF ANAEROBIC CARBON MINERALIZATION RATES TO SULFATE AMENDMENTS IN A BOREAL PEATLAND

A small body of research suggests that dissimilatory sulfate reduction can affect the carbon balance of peatlands, yet this has not been tested widely, despite the fact that peatlands contain approximately one-third of the global soil carbon pool. Here we evaluate the role of dissimilatory sulfate reduction in a site that receives low atmospheric sulfur deposition. We hypothesized that, in peatlands receiving low sulfate inputs, methane production should dominate anaerobic carbon mineralization. We further hypothesized that with sulfate amendments, anaerobic carbon mineralization could show an overall increase if terminal carbon mineralization in unamended peat is limited by an inadequate supply of electron acceptors. To test these hypotheses, we delineated six 1-m2 plots in an ombrotrophic, boreal peatland in central Alberta, Canada (Bleak Lake Bog), which receives <2 mmol S·m−2·yr−1. Three of the plots were amended with sulfate (78 mmol S·m−2·yr−1). We measured anaerobic rates of sulfate reduction, CH4 production, and CO2 production. In opposition to our hypotheses, sulfate amendments did not increase rates of sulfate reduction, increase CO2 production, or decrease CH4 production over a 2-yr period, but did increase both sulfate pool sizes and residence times. Despite low rates of sulfate reduction compared to other freshwater wetlands, daily average sulfate reduction (1.7 mmol/m2) exceeded regional annual inputs of atmospheric sulfate deposition (1.6 mmol/m2). Between 77% and 99% of reduced sulfate was incorporated into the carbon-bonded sulfur pool, which turns over slowly. The slow turnover rate and comparatively low sulfate reduction rates may be related to the low iron content of the bog peat. Additionally, sulfate reduction initially was sulfate limited in the control plots, but with sulfur amendments, the sulfate limitation was removed; sulfate reduction appeared to be limited by some other factor, possibly labile carbon. Dissimilatory sulfate reduction was more important to total anaerobic carbon mineralization than methane production, although neither process dominated overall anaerobic carbon mineralization (<2% of total). Fermentation appeared to be the dominant anaerobic carbon mineralization pathway at Bleak Lake Bog, yet the mechanisms of how this process affects the carbon balance of peatlands has never been evaluated. Overall, our results suggest that, in at least the short term, soil carbon turnover in peatlands will not be enhanced by increased atmospheric sulfur deposition. If we want to understand the controlling factors on soil carbon storage in sites like Bleak Lake Bog, we should begin to examine anaerobic carbon mineralization via fermentation pathways. Corresponding Editor: J. M. Melack

Past, Present, and Future Peatland Carbon Balance: An Empirical Model Based on 210 Pb-Dated Cores

Past, Present, and Future Peatland Carbon Balance: An Empirical Model Based on 210 Pb-Dated Cores

Growth Response of Sphagnum capillifolium to Nighttime Temperature and Nutrient Level: Mechanisms and Implications for Global Change

Individuals of Sphagnum capillifolium were cultured for 2 mo under six different combinations of nighttime temperature and nutrients. Low nighttime temperature caused a five-fold reduction of growth. Growth was also reduced when the plants were cultured without any addition of nutrient in the growing medium, but only when nutrient deficiency was coupled with high nighttime temperature. Growth reduction was associated with decreased rates of net photosynthesis, but was not accompanied by a degradation of photosynthetic pigments and/or variations in the pigment ratios, nor was the ultrastructure of chloroplasts significantly altered. The decline in the net photosynthetic rate may be due to a limitation in the enzymatic reactions at unfavorable temperatures. Nitrogen and, especially, phosphorus appeared to limit growth of Sphagnum capillifolium at optimal temperatures. A nighttime temperature of 50C was above the lower threshold triggering the synthesis of red wall-pigments, known to be promoted by nighttime chilling. Climate warming is expected to increase the growth rates of Sphagnum, but the consequences on the carbon balance of peatlands cannot be predicted because temperature rise may also enhance breakdown of peat.

Growth Response of Sphagnum capillifolium to Nighttime Temperature and Nutrient Level: Mechanisms and Implications for Global Change

Individuals of Sphagnum capillifolium were cultured for 2 mo under six different combinations of nighttime temperature and nutrients. Low nighttime temperature caused a five-fold reduction of growth. Growth was also reduced when the plants were cultured without any addition of nutrient in the growing medium, but only when nutrient deficiency was coupled with high nighttime temperature. Growth reduction was associated with decreased rates of net photosynthesis, but was not accompanied by a degradation of photosynthetic pigments and/or variations in the pigment ratios, nor was the ultrastructure of chloroplasts significantly altered. The decline in the net photosynthetic rate may be due to a limitation in the enzymatic reactions at unfavorable temperatures. Nitrogen and, especially, phosphorus appeared to limit growth of Sphagnum capillifolium at optimal temperatures. A nighttime temperature of 5°C was above the lower threshold triggering the synthesis of red wall-pigments, known to be promoted by nighttime chilling. Climate warming is expected to increase the growth rates of Sphagnum, but the consequences on the carbon balance of peatlands cannot be predicted because temperature rise may also enhance breakdown of peat.

Disappearing Peat-Regenerating Peat? The Impact of Climate Change on British Peatlands

On a global scale, over the past 200 years peatlands have become a source rather than a sink of carbon. Drainage for agriculture, forestry and peat extraction have resulted in a 16-37 per cent loss in the carbon sink capacity. The current scenarios for climate change in Britain will exacerbate this loss. A shift in the carbon balance of peatlands is not necessarily the only outcome of climate change. Indirect hydrological changesespecially alteration of the position of the peat water table-will affect the stability of peatland ecosystems. This raises a number of questions concerning the future of British peatlands: the most important of which is how will the water balance change on a regional scale? In Britain the potential response of peatlands to climate change varies spatially. In upland areas, where rainfall is the main source of water, the key question is will erosion increase and if so, how fast? It will also be important to establish the drainage network response in terms of run-off, sediment loading and stream water quality. Increased precipitation may increase the rate of sedimentation in reservoirs thus affecting their water-holding capacity and water quality. Enhanced decomposition at elevated temperatures may also increase the microbial release of humic acids and increase the incidence of colour in upland waters which will in turn increase the cost of water quality treatment. In lowland Britain, the increased flood risk and more or less permanently elevated water table (as a result of both a rising sea level and sinking land surface) may enable peat regeneration through paludification. Key areas that are likely to be affected have spring or floodwater as their main source of water. They include the Norfolk Broads, Suffolk valley peats, Cambridgeshire Fens, Humberhead Levels, Derwent Ings and possibly the Somerset and Gwent Levels. In order to minimize the effects of climate change on peatlands and to preserve their existing carbon sink capacity (however small) they must remain hydrologically intact, and as high a water table as possible must be maintained. This may be possible in low-lying areas if flooding reinstates paludification but the process of peat regeneration is a slow one. In upland areas the effect of climate change is less clear; increased precipitation may encourage peat formation but it may also result in greater erosion.