Publications by year
In Press
Treat CC, Jones MC, Camill P, Gallego-Sala AV, Garneau M, Harden JW, Hugelius G, Klein ES, Kokfelt U, Kuhry P, et al (In Press). Effects of permafrost aggradation on peat properties as determined from a pan-arctic synthesis of plant macrofossils.
Journal of Geophysical Research Biogeosciences,
120Abstract:
Effects of permafrost aggradation on peat properties as determined from a pan-arctic synthesis of plant macrofossils
Permafrost dynamics play an important role in high-latitude peatland carbon balance and are key to understanding the future response of soil carbon stocks. Permafrost aggradation can control the magnitude of the carbon feedback in peatlands through effects on peat properties. We compiled peatland plant macrofossil records for the northern permafrost zone (515 cores from 280 sites) and classified samples by vegetation type and environmental class (fen, bog, tundra and boreal permafrost, thawed permafrost). We examined differences in peat properties (bulk density, carbon (C), nitrogen (N) and organic matter content, C/N ratio) and C accumulation rates among vegetation types and environmental classes. Consequences of permafrost aggradation differed between boreal and tundra biomes, including differences in vegetation composition, C/N ratios, and N content. The vegetation composition of tundra permafrost peatlands was similar to permafrost-free fens, while boreal permafrost peatlands more closely resembled permafrost-free bogs. Nitrogen content in boreal permafrost and thawed permafrost peatlands was significantly lower than in permafrost-free bogs despite similar vegetation types (0.9% versus 1.5% N). Median long-term C accumulation rates were higher in fens (23 g C m-2 y-1) than in permafrost-free bogs (18 g C m-2 y-1), and were lowest in boreal permafrost peatlands (14 g C m-2 y-1). The plant macrofossil record demonstrated transitions from fens to bogs to permafrost peatlands, bogs to fens, permafrost aggradation within fens, and permafrost thaw and re-aggradation. Using data synthesis, we've identified predominant peatland successional pathways, changes in vegetation type, peat properties, and C accumulation rates associated with permafrost aggradation.
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Cooper CL, Swindles GT, Watson ET, Savov IP, Galka M, Gallego-Sala AV, Borken W (In Press). Evaluating tephrochronology in the permafrost peatlands of Northern Sweden.
Quaternary Geochronology Full text.
New SL, Belcher C, Hudspith VA, Gallego-Sala AV (In Press). Holocene fire history: can evidence of peat burning be found in the palaeo-archive?.
Mires and Peat,
18, 1-11.
Abstract:
Holocene fire history: can evidence of peat burning be found in the palaeo-archive?
Smouldering wildfires in peatlands have the potential to release substantial amounts of the carbon currently sequestered in these ecosystems. However, past studies of Holocene fire history in peatlands have given little consideration to the identification of evidence left behind after peat burning, or to charring of the peat matrix. In this study, modern peat samples from peatlands across the globe were charred in order to assess the identifiable characteristics of charred peat. On this basis we believe that charred aggregates of partially decayed organics which can be identified in cores provide clear evidence that the peat matrix itself burned. A range of
charred morphotypes could be found throughout a 2 m peat core from
and we are able to identify charred partially decayed aggregates that appeared to correspond with peaks in fire activity on the bog. These may reflect periods when surface fires ignited the peat surface below, or when the radiant heat from surface fires was sufficient to pyrolyse the surface peat. We conclude that it is possible to find evidence of peat burning in the palaeo-archive, and that future studies should begin to document the occurrence of charred particles so that the discipline can begin to build a picture of possible past peat fire
activity.
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Naafs BDA, Inglis GN, Zheng Y, Amesbury MJ, Biester H, Bindler R, Blewett J, Burrows MA, del Castillo Torres D, Chambers FM, et al (In Press). Introducing global peat-specific temperature and pH calibrations based on brGDGT bacterial lipids.
Geochimica et Cosmochimica Acta Full text.
Zhang H, Amesbury M, Piilo S, Garneau M, Gallego-Sala A, Väliranta M (In Press). Recent changes in peatland testate amoeba functional traits and hydrology within a replicated site network in northwestern Québec, Canada. Frontiers in Ecology and Evolution, section Paleoecology
Piilo SR, Zhang H, Garneau M, Gallego-Sala AV, Amesbury M, Väliranta M (In Press). Recent peat and carbon accumulation following the Little Ice Age in northwestern Québec, Canada.
Environmental Research Letters Full text.
Naafs BDA, Gallego-Sala AV, Inglis GN, Pancost RD (In Press). Refining the global branched glycerol dialkyl glycerol tetraether (brGDGT) soil temperature calibration.
Organic Geochemistry Full text.
Davis TW, Prentice IC, Stocker BD, Whitely RJ, Wang H, Evans BJ, Gallego-Sala AV, Sykes MT, Cramer W (In Press). Simple Process-Led Algorithms for Simulating Habitats (SPLASH v.1.0): Robust Indices of Radiation, Evapotranspiration and Plant-Available Moisture.
Abstract:
Simple Process-Led Algorithms for Simulating Habitats (SPLASH v.1.0): Robust Indices of Radiation, Evapotranspiration and Plant-Available Moisture
Abstract. Bioclimatic indices for use in studies of ecosystem function, species distribution, and vegetation dynamics under changing climate scenarios depend on estimates of surface fluxes and other quantities, such as radiation, evapotranspiration and soil moisture, for which direct observations are sparse. These quantities can be derived indirectly from meteorological variables, such as air temperature, precipitation and cloudiness. Here we present a consolidated set of Simple Process-Led Algorithms for Simulating Habitats (SPLASH) allowing robust approximations of key quantities at ecologically relevant time scales. We specify equations, derivations, simplifications and assumptions for the estimation of daily and monthly quantities of top-of-the-atmosphere solar radiation, net surface radiation, photosynthetic photon flux density, evapotranspiration (potential, equilibrium and actual), condensation, soil moisture, and runoff, based on analysis of their relationship to fundamental climatic drivers. SPLASH, as presented here, is designed for application at discrete locations; however, the same methodology can naturally be applied to spatial grids. The climatic drivers include a minimum of three meteorological inputs: precipitation, air temperature, and either fraction of bright sunshine hours or fractional cloud cover. Indices, such as the moisture index, the climatic water deficit, and the Priestley-Taylor coefficient, are also defined. The SPLASH code is transcribed in C++, FORTRAN, Python, and R. One year of results from a specific location are provided to exemplify the daily and monthly model outputs, following a two-year spin-up of soil moisture content.
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Zhang H, Piilo S, Amesbury M, Charman D, Gallego-Sala AV, Väliranta M (In Press). The role of climate change in regulating Arctic permafrost peatland hydrological and vegetation change over the last millennium.
Quaternary Science Reviews Full text.
Bohn TJ, Melton JR, Ito A, Kleinen T, Spahni R, Stocker BD, Zhang B, Zhu X, Schroeder. R, Glagolev MV, et al (In Press). WETCHIMP-WSL: intercomparison of wetland methane emissions models over West Siberia.
Biogeosciences Discuss.,
12, 1907-1973.
Abstract:
WETCHIMP-WSL: intercomparison of wetland methane emissions models over West Siberia
Wetlands are the world's largest natural source of methane, a powerful greenhouse gas. The strong sensitivity of methane emissions to environmental factors such as soil temperature and moisture has led to concerns about potential positive feedbacks to climate change. This risk is particularly relevant at high latitudes, which have experienced pronounced warming and where thawing permafrost could potentially liberate large amounts of labile carbon over the next 100 years. However, global models disagree as to the magnitude and spatial distribution of emissions, due to uncertainties in wetland area and emissions per unit area and a scarcity of in situ observations. Recent intensive field campaigns across the West Siberian Lowland (WSL) make this an ideal region over which to assess the performance of large-scale process-based wetland models in a high-latitude environment. Here we present the results of a follow-up to the Wetland and Wetland CH4 Intercomparison of Models Project (WETCHIMP), focused on the West Siberian Lowland (WETCHIMP-WSL). We assessed 21 models and 5 inversions over this domain in terms of total CH4 emissions, simulated wetland areas, and CH4 fluxes per unit wetland area and compared these results to an intensive in situ CH4 flux dataset, several wetland maps, and two satellite inundation products. We found that: (a) despite the large scatter of individual estimates, 12 year mean estimates of annual total emissions over the WSL from forward models (5.34 ± 0.54 Tg CH4 y-1), inversions (6.06 ± 1.22 Tg CH4 y-1), and in situ observations (3.91 ± 1.29 Tg CH4 y-1) largely agreed, (b) forward models using inundation products alone to estimate wetland areas suffered from severe biases in CH4 emissions, (c) the interannual timeseries of models that lacked either soil thermal physics appropriate to the high latitudes or realistic emissions from unsaturated peatlands tended to be dominated by a single environmental driver (inundation or air temperature), unlike those of inversions and more sophisticated forward models, (d) differences in biogeochemical schemes across models had relatively smaller influence over performance; and (e) multi-year or multi-decade observational records are crucial for evaluating models' responses to long-term climate change.
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2020
Lewis K, Rumpang E, Kho LK, McCalmont J, Teh YA, Gallego-Sala A, Hill TC (2020). An assessment of oil palm plantation aboveground biomass stocks on tropical peat using destructive and non-destructive methods.
Scientific Reports,
10(1).
Abstract:
An assessment of oil palm plantation aboveground biomass stocks on tropical peat using destructive and non-destructive methods
© 2020, the Author(s). The recent expansion of oil palm (OP, Elaeis guineensis) plantations into tropical forest peatlands has resulted in ecosystem carbon emissions. However, estimates of net carbon flux from biomass changes require accurate estimates of the above ground biomass (AGB) accumulation rate of OP on peat. We quantify the AGB stocks of an OP plantation on drained peat in Malaysia from 3 to 12 years after planting using destructive harvests supported by non-destructive surveys of a further 902 palms. Peat specific allometric equations for palm (R2 = 0.92) and frond biomass are developed and contrasted to existing allometries for OP on mineral soils. Allometries are used to upscale AGB estimates to the plantation block-level. Aboveground biomass stocks on peat accumulated at ~6.39 ± 1.12 Mg ha−1 per year in the first 12 years after planting, increasing to ~7.99 ± 0.95 Mg ha−1 yr−1 when a ‘perfect’ plantation was modelled. High inter-palm and inter-block AGB variability was observed in mature classes as a result of variations in palm leaning and mortality. Validation of the allometries defined and expansion of non-destructive inventories across alternative plantations and age classes on peat would further strengthen our understanding of peat OP AGB accumulation rates.
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Ritchie P, Smith G, Davis K, Fezzi C, Halleck-Vega S, Harper A, Boulton C, Binner A, Day B, Gallego-Sala A, et al (2020). Shifts in national land use and food production in Great Britain after a climate tipping point.
Nature Food,
1, 76-83.
Full text.
2019
Blewett J, Naafs BDA, Gallego-Sala AV, Pancost RD (2019). A novel proxy based on archaeal lipids for tropical terrestrial temperatures in ancient greenhouse climates.
Blewett J, Naafs BDA, Gallego-Sala AV, Pancost RD (2019). A novel proxy based on archaeal lipids for tropical terrestrial temperatures in ancient greenhouse climates.
Blewett J, Naafs BDA, Gallego-Sala AV, Pancost RD (2019). A novel proxy based on archaeal lipids for tropical terrestrial temperatures in ancient greenhouse climates.
Martínez Cortizas A, López-Costas O, Orme L, Mighall T, Kylander ME, Bindler R, Gallego Sala Á (2019). Holocene atmospheric dust deposition in NW Spain.
The Holocene,
30(4), 507-518.
Abstract:
Holocene atmospheric dust deposition in NW Spain
Atmospheric dust plays an important role in terrestrial and marine ecosystems, particularly those that are nutrient limited. Despite that most dust originates from arid and semi-arid regions, recent research has shown that past dust events may have been involved in boosting productivity in nutrient-poor peatlands. We investigated dust deposition in a mid-latitude, raised bog, which is surrounded by a complex geology (paragneiss/schist, granite, quartzite and granodiorite). As proxies for dust fluxes, we used accumulation rates of trace (Ti, Zr, Rb, Sr and Y) as well as major (K and Ca) lithogenic elements. The oldest, largest dust deposition event occurred between ~8.6 and ~7.4 ka BP, peaking at ~8.1 ka BP (most probably the 8.2 ka BP event). The event had a large impact on the evolution of the mire, which subsequently transitioned from a fen into a raised bog in ~1500 years. From ~6.7 to ~4.0 ka BP, fluxes were very low, coeval with mid-Holocene forest stability and maximum extent. In the late Holocene, after ~4.0 ka BP, dust events became more prevalent with relatively major deposition at ~3.2–2.5, ~1.4 ka BP and ~0.35–0.05 ka BP, and minor peaks at ~4.0–3.7, ~1.7, ~1.10–0.95 ka BP and ~0.74–0.58 ka BP. Strontium fluxes display a similar pattern between ~11 and ~6.7 ka BP but then became decoupled from the other elements from the mid Holocene onwards. This seems to be a specific signal of the granodiorite batholith, which has an Sr anomaly. The reconstructed variations in dust fluxes bear a strong climatic imprint, probably related to storminess controlled by North Atlantic Oscillation conditions. Complex interactions also arise because of increased pressure from human activities.
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Young DM, Baird AJ, Charman DJ, Evans CD, Gallego-Sala AV, Gill PJ, Hughes PDM, Morris PJ, Swindles GT (2019). Misinterpreting carbon accumulation rates in records from near-surface peat.
Sci Rep,
9(1).
Abstract:
Misinterpreting carbon accumulation rates in records from near-surface peat.
Peatlands are globally important stores of carbon (C) that contain a record of how their rates of C accumulation have changed over time. Recently, near-surface peat has been used to assess the effect of current land use practices on C accumulation rates in peatlands. However, the notion that accumulation rates in recently formed peat can be compared to those from older, deeper, peat is mistaken - continued decomposition means that the majority of newly added material will not become part of the long-term C store. Palaeoecologists have known for some time that high apparent C accumulation rates in recently formed peat are an artefact and take steps to account for it. Here we show, using a model, how the artefact arises. We also demonstrate that increased C accumulation rates in near-surface peat cannot be used to infer that a peatland as a whole is accumulating more C - in fact the reverse can be true because deep peat can be modified by events hundreds of years after it was formed. Our findings highlight that care is needed when evaluating recent C addition to peatlands especially because these interpretations could be wrongly used to inform land use policy and decisions.
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Author URL.
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Amesbury MJ, Gallego-Sala A, Loisel J (2019). Peatlands as prolific carbon sinks.
Nature Geoscience,
12(11), 880-881.
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Whittle A, Amesbury MJ, Charman DJ, Hodgson DA, Perren BB, Roberts SJ, Gallego-Sala AV (2019). Salt-Enrichment Impact on Biomass Production in a Natural Population of Peatland Dwelling Arcellinida and Euglyphida (Testate Amoebae).
Microb Ecol,
78(2), 534-538.
Abstract:
Salt-Enrichment Impact on Biomass Production in a Natural Population of Peatland Dwelling Arcellinida and Euglyphida (Testate Amoebae).
Unicellular free-living microbial eukaryotes of the order Arcellinida (Tubulinea; Amoebozoa) and Euglyphida (Cercozoa; SAR), commonly termed testate amoebae, colonise almost every freshwater ecosystem on Earth. Patterns in the distribution and productivity of these organisms are strongly linked to abiotic conditions-particularly moisture availability and temperature-however, the ecological impacts of changes in salinity remain poorly documented. Here, we examine how variable salt concentrations affect a natural community of Arcellinida and Euglyphida on a freshwater sub-Antarctic peatland. We principally report that deposition of wind-blown oceanic salt-spray aerosols onto the peatland surface corresponds to a strong reduction in biomass and to an alteration in the taxonomic composition of communities in favour of generalist taxa. Our results suggest novel applications of this response as a sensitive tool to monitor salinisation of coastal soils and to detect salinity changes within peatland palaeoclimate archives. Specifically, we suggest that these relationships could be used to reconstruct millennial scale variability in salt-spray deposition-a proxy for changes in wind-conditions-from sub-fossil communities of Arcellinida and Euglyphida preserved in exposed coastal peatlands.
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Harrison ME, Ottay JB, D’Arcy LJ, Cheyne SM, Anggodo, Belcher C, Cole L, Dohong A, Ermiasi Y, Feldpausch T, et al (2019). Tropical forest and peatland conservation in Indonesia: Challenges and directions.
People and Nature,
2(1), 4-28.
Full text.
Swindles GT, Morris PJ, Mullan DJ, Payne RJ, Roland TP, Amesbury MJ, Lamentowicz M, Turner TE, Gallego-Sala A, Sim T, et al (2019). Widespread drying of European peatlands in recent centuries.
Nature Geoscience,
12(11), 922-928.
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Inglis GN, Naafs BDA, Zheng Y, Schellekens J, Pancost RD, Amesbury MJ, Biester H, Bindler R, Blewett J, Burrows MA, et al (2019). delta C-13 values of bacterial hopanoids and leaf waxes as tracers for methanotrophy in peatlands.
GEOCHIMICA ET COSMOCHIMICA ACTA,
260, 244-256.
Author URL.
2018
Inglis GN, Naafs BDA, Zheng Y, McClymont EL, Evershed RP, Pancost RD, the T-GRES Peat Database collaborators (2018). Distributions of geohopanoids in peat: Implications for the use of hopanoid-based proxies in natural archives.
Geochimica et Cosmochimica Acta,
224, 249-261.
Abstract:
Distributions of geohopanoids in peat: Implications for the use of hopanoid-based proxies in natural archives
Hopanoids are pentacyclic triterpenoids produced by a wide range of bacteria. Within modern settings, hopanoids mostly occur in the biological 17β,21β(H) configuration. However, in some modern peatlands, the C31 hopane is present as the ‘thermally-mature’ 17α,21β(H) stereoisomer. This has traditionally been ascribed to isomerisation at the C-17 position catalysed by the acidic environment. However, recent work has argued that temperature and/or hydrology also exert a control upon hopane isomerisation. Such findings complicate the application of geohopanoids as palaeoenvironmental proxies. However, due to the small number of peats that have been studied, as well as the lack of peatland diversity sampled, the environmental controls regulating geohopanoid isomerisation remain poorly constrained. Here, we undertake a global approach to investigate the occurrence, distribution and diagenesis of geohopanoids within peat, combining previously published and newly generated data (n = 395) from peatlands with a wide temperature (−1 to 27 °C) and pH (3–8) range. Our results indicate that peats are characterised by a wide range of geohopanoids. However, the C31 hopane and C32 hopanoic acid (and occasionally the C32 hopanol) typically dominate. C32 hopanoic acids occur as αβ- and ββ-stereoisomers, with the ββ-isomer typically dominating. In contrast, C31 hopanes occur predominantly as the αβ-stereoisomer. These two observations collectively suggest that isomerisation is not inherited from an original biological precursor (i.e. biohopanoids). Using geohopanoid ββ/(αβ + ββ) indices, we demonstrate that the abundance of αβ-hopanoids is strongly influenced by the acidic environment, and we observe a significant positive correlation between C31 hopane isomerisation and pH (n = 94, r2 = 0.64, p 1 pH unit) and longer-term (>1 kyr) variation. Overall, our findings demonstrate the potential of geohopanoids to provide unique new insights into understanding depositional environments and interpreting terrestrial organic matter sources in the geological record.
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Zhang H, Gallego-Sala AV, Amesbury M, Charman D, Piilo SR, Väliranta M (2018). Inconsistent response of Arctic permafrost peatland carbon accumulation to warm climate phases.
Global Biogeochemical CyclesAbstract:
Inconsistent response of Arctic permafrost peatland carbon accumulation to warm climate phases
Northern peatlands have accumulated large carbon (C) stocks since the last deglaciation and during past millennia they have acted as important atmospheric C sinks. However, it is still poorly understood how northern peatlands in general and Arctic permafrost peatlands in particular will respond to future climate change. In this study, we present C accumulation reconstructions derived from 14 peat cores from four permafrost peatlands in northeast European Russia and Finnish Lapland. The main focus is on warm climate phases. We used regression analyses to test the importance of different environmental variables such as summer temperature, hydrology and vegetation as drivers for non‐autogenic C accumulation. We used modeling approaches to simulate potential decomposition patterns. The data show that our study sites have been persistent mid‐ to late‐Holocene C sinks with an average accumulation rate of 10.80 – 32.40 g C m‐2 y‐1. The warmer climate phase during the Holocene Thermal Maximum stimulated faster apparent C accumulation rates (ACARs) while the Medieval Climate Anomaly did not. Moreover, during the Little Ice Age, ACARs were controlled more by other factors than by cold climate per se. Although we could not identify any significant environmental factor that drove C accumulation, our data show that recent warming has increased C accumulation in some permafrost peatland sites. However, the synchronous slight decrease of C accumulation in other sites may be an alternative response of these peatlands to warming in the future. This would lead to a decrease in the C sequestration ability of permafrost peatlands overall.
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Gallego-Sala AV, Charman D, Brewer S, Page SE, Prentice IC, Friedlingstein P, Moreton S, Amesbury MJ, Beilman DW, Björck S, et al (2018). Latitudinal limits to the predicted increase of the peatland carbon sink with warming.
Nature Climate Change,
8, 907-913.
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2017
Swindles GT, Morris PJ, Whitney B, Galloway JM, Gałka M, Gallego-Sala AV, Macumber AL, Mullan D, Smith MW, Amesbury MJ, et al (2017). Ecosystem state shifts during long-term development of an Amazonian peatland.
Global Change BiologyAbstract:
Ecosystem state shifts during long-term development of an Amazonian peatland
The most carbon (C) dense ecosystems of Amazonia are areas characterised by the presence of peatlands. However, Amazonian peatland ecosystems are poorly understood and are threatened by human activities. Here we present an investigation into long-term ecohydrological controls on C accumulation in an Amazonian peat dome. This site is the oldest peatland yet discovered in Amazonia (peat initiation c. 8.9 ka BP), and developed in three stages; (i) peat initiated in an abandoned river channel with open water and aquatic plants; (ii) inundated forest swamp; and (iii) raised peat dome (since c. 3.9 ka BP). Local burning occurred at least three times in the past 4,500 years. Two phases of particularly rapid C accumulation (c. 6.6-6.1 and c. 4.9-3.9 ka BP), potentially resulting from increased net primary productivity, were seemingly driven by drier conditions associated with widespread drought events. The association of drought phases with major ecosystem state shifts (open water wetland – forest swamp – peat dome) suggests a potential climatic control on the developmental trajectory of this tropical peatland. A third drought phase centred on c. 1.8-1.1 ka BP led to markedly reduced C accumulation and potentially a hiatus during the peat dome stage. Our results suggest that future droughts may lead to phases of rapid C accumulation in some inundated tropical peat swamps, although this can lead ultimately to a shift to ombrotrophy and a subsequent return to slower C accumulation. Conversely, in ombrotrophic peat domes, droughts may lead to reduced C accumulation or even net loss of peat. Increased surface wetness at our site in recent decades may reflect a shift towards a wetter climate in western Amazonia. Amazonian peatlands represent important carbon stores and habitats, and are important archives of past climatic and ecological information. They should form key foci for conservation efforts.
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Davis TW, Prentice IC, Stocker BD, Thomas RT, Whitley RJ, Wang H, Evans BJ, Gallego-Sala AV, Sykes MT, Cramer W, et al (2017). Simple process-led algorithms for simulating habitats (SPLASH v.1.0): Robust indices of radiation, evapotranspiration and plant-available moisture.
Geoscientific Model Development,
10(2), 689-708.
Abstract:
Simple process-led algorithms for simulating habitats (SPLASH v.1.0): Robust indices of radiation, evapotranspiration and plant-available moisture
© Author(s) 2017. Bioclimatic indices for use in studies of ecosystem function, species distribution, and vegetation dynamics under changing climate scenarios depend on estimates of surface fluxes and other quantities, such as radiation, evapotranspiration and soil moisture, for which direct observations are sparse. These quantities can be derived indirectly from meteorological variables, such as near-surface air temperature, precipitation and cloudiness. Here we present a consolidated set of simple process-led algorithms for simulating habitats (SPLASH) allowing robust approximations of key quantities at ecologically relevant timescales. We specify equations, derivations, simplifications, and assumptions for the estimation of daily and monthly quantities of top-of-the-atmosphere solar radiation, net surface radiation, photosynthetic photon flux density, evapotranspiration (potential, equilibrium, and actual), condensation, soil moisture, and runoff, based on analysis of their relationship to fundamental climatic drivers. The climatic drivers include a minimum of three meteorological inputs: precipitation, air temperature, and fraction of bright sunshine hours. Indices, such as the moisture index, the climatic water deficit, and the Priestley-Taylor coefficient, are also defined. The SPLASH code is transcribed in C++, FORTRAN, Python, and R. A total of 1 year of results are presented at the local and global scales to exemplify the spatiotemporal patterns of daily and monthly model outputs along with comparisons to other model results.
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Zhang H, Amesbury MJ, Ronkainen T, Charman DJ, Gallego-Sala AV, Valiranta M (2017). Testate amoeba as palaeohydrological indicators in the permafrost peatlands of north-east European Russia and Finnish Lapland.
Journal of Quaternary ScienceAbstract:
Testate amoeba as palaeohydrological indicators in the permafrost peatlands of north-east European Russia and Finnish Lapland
To explore the use of testate amoeba for investigating the impacts of climate change on permafrost peatland hydrology, we established a new modern training set from Arctic permafrost peatlands in north-east European Russia and Finnish Lapland. Ordination analyses showed that water-table depth (WTD) was the most important control on testate amoeba distribution. We developed a new testate amoeba-based WTD transfer function and thoroughly tested it. We found that our transfer function had strong predictive power. The best- performing model was based on tolerance-downweighted weighted averaging with inverse deshrinking (R2 1⁄4 0.77, RMSEP 1⁄4 5.62 cm with leave-one-out cross validation). The new transfer function was applied to a short peat core from Arctic Russia and revealed two major hydrological shifts, which could be validated against plant macrofossil data. We also compared our model to another two models from more temperate peatlands. Comparison of the different testate amoeba datasets suggests that testate amoeba ecohydrological relationships are similar for permafrost peatlands to those in more temperate regions, but there are some differences that suggest a need for training datasets that are fully representative of permafrost peatlands.
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Gałka M, Szal M, Watson EJ, Gallego-Sala A, Amesbury MJ, Charman DJ, Roland TP, Edward Turner T, Swindles GT (2017). Vegetation Succession, Carbon Accumulation and Hydrological Change in Subarctic Peatlands, Abisko, Northern Sweden.
Permafrost and Periglacial Processes,
28(4), 589-604.
Abstract:
Vegetation Succession, Carbon Accumulation and Hydrological Change in Subarctic Peatlands, Abisko, Northern Sweden
Copyright © 2017 John Wiley. &. Sons, Ltd. High-resolution analyses of plant macrofossils, testate amoebae, pollen, mineral content, bulk density, and carbon and nitrogen were undertaken to examine the late Holocene dynamics of two permafrost peatlands in Abisko, Subarctic Sweden. The peat records were dated using tephrochronology, 14C and 210Pb. Local plant succession and hydrological changes in peatlands were synchronous with climatic shifts, although autogenous plant succession towards ombrotrophic status during peatland development was also apparent. The Marooned peatland experienced a shift ca. 2250 cal yr BP from rich to poor fen, as indicated by the appearance of Sphagnum fuscum. At Stordalen, a major shift to wetter conditions occurred between 500 and 250 cal yr BP, probably associated with climate change during the Little Ice Age. During the last few decades, the testate amoeba data suggest a deepening of the water table and an increase in shrub pollen, coinciding with recent climate warming and the associated expansion of shrub communities across the Arctic. Rates of carbon accumulation vary greatly between the sites, illustrating the importance of local vegetation communities, hydrology and permafrost dynamics. Multiproxy data elucidate the palaeoecology of S. lindbergii and show that it indicates wet conditions in peatlands. Copyright © 2017 John Wiley & Sons, Ltd.
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2016
Gallego-Sala AV, Charman DJ, Harrison SP, Li G, Prentice IC (2016). Climate-driven expansion of blanket bogs in Britain during the Holocene.
Climate of the Past,
12(1), 129-136.
Abstract:
Climate-driven expansion of blanket bogs in Britain during the Holocene
© 2016 Author(s). Blanket bog occupies approximately 6 % of the area of the UK today. The Holocene expansion of this hyperoceanic biome has previously been explained as a consequence of Neolithic forest clearance. However, the present distribution of blanket bog in Great Britain can be predicted accurately with a simple model (PeatStash) based on summer temperature and moisture index thresholds, and the same model correctly predicts the highly disjunct distribution of blanket bog worldwide. This finding suggests that climate, rather than land-use history, controls blanket-bog distribution in the UK and everywhere else. We set out to test this hypothesis for blanket bogs in the UK using bioclimate envelope modelling compared with a database of peat initiation age estimates. We used both pollen-based reconstructions and climate model simulations of climate changes between the mid-Holocene (6000 yr BP, 6 ka) and modern climate to drive PeatStash and predict areas of blanket bog. We compiled data on the timing of blanket-bog initiation, based on 228 age determinations at sites where peat directly overlies mineral soil. The model predicts that large areas of northern Britain would have had blanket bog by 6000 yr BP, and the area suitable for peat growth extended to the south after this time. A similar pattern is shown by the basal peat ages and new blanket bog appeared over a larger area during the late Holocene, the greatest expansion being in Ireland, Wales, and southwest England, as the model predicts. The expansion was driven by a summer cooling of about 2 °C, shown by both pollen-based reconstructions and climate models. The data show early Holocene (pre-Neolithic) blanket-bog initiation at over half of the sites in the core areas of Scotland and northern England. The temporal patterns and concurrence of the bioclimate model predictions and initiation data suggest that climate change provides a parsimonious explanation for the early Holocene distribution and later expansion of blanket bogs in the UK, and it is not necessary to invoke anthropogenic activity as a driver of this major landscape change.
Abstract.
Full text.
Gallego-Sala AV, Booth RK, Charman DJ, Prentice IC, Yu Z (2016). Peatlands and Climate Change. In Bonn A, Allott T, Evans M, Joosten H, Stoneman R (Eds.)
Peatland Restoration and Ecosystem Services
Science, Policy and Practice, Cambridge University Press.
Abstract:
Peatlands and Climate Change
Abstract.
Full text.
2015
Amesbury MJ, Charman DJ, Newnham RM, Loader NJ, Goodrich J, Royles J, Campbell DI, Keller ED, Baisden WT, Roland TP, et al (2015). Can oxygen stable isotopes be used to track precipitation moisture source in vascular plant-dominated peatlands?.
Earth and Planetary Science Letters,
430, 149-159.
Abstract:
Can oxygen stable isotopes be used to track precipitation moisture source in vascular plant-dominated peatlands?
© 2015 the Authors. Variations in the isotopic composition of precipitation are determined by fractionation processes which occur during temperature- and humidity-dependent phase changes associated with evaporation and condensation. Oxygen stable isotope ratios have therefore been frequently used as a source of palaeoclimate data from a variety of proxy archives, which integrate this signal over time. Applications from ombrotrophic peatlands, where the source water used in cellulose synthesis is derived solely from precipitation, have been mostly limited to Northern Hemisphere Sphagnum-dominated bogs, with few in the Southern Hemisphere or in peatlands dominated by vascular plants. New Zealand (NZ) provides an ideal location to undertake empirical research into oxygen isotope fractionation in vascular peatlands because single taxon analysis can be easily carried out, in particular using the preserved root matrix of the restionaceous wire rush (Empodisma spp.) that forms deep Holocene peat deposits throughout the country. Furthermore, large gradients are observed in the mean isotopic composition of precipitation across NZ, caused primarily by the relative influence of different climate modes. Here, we test whether δ18O of Empodisma α-cellulose from ombrotrophic restiad peatlands in NZ can provide a methodology for developing palaeoclimate records of past precipitation δ18O. Surface plant, water and precipitation samples were taken over spatial (six sites spanning >10° latitude) and temporal (monthly measurements over one year) gradients. A link between the isotopic composition of root-associated water, the most likely source water for plant growth, and precipitation in both datasets was found. Back-trajectory modelling of precipitation moisture source for rain days prior to sampling showed clear seasonality in the temporal data that was reflected in root-associated water. The link between source water and plant cellulose was less clear, although mechanistic modelling predicted mean cellulose values within published error margins for both datasets. Improved physiological understanding and modelling of δ18O in restiad peatlands should enable use of this approach as a new source of palaeoclimate data to reconstruct changes in past atmospheric circulation.
Abstract.
Amesbury MJ, Charman DJ, Newnham RM, Loader NJ, Goodrich JP, Royles J, Campbell DI, Roland TP, Gallego-Sala A (2015). Carbon stable isotopes as a palaeoclimate proxy in vascular plant dominated peatlands.
Geochimica et Cosmochimica Acta,
164, 161-174.
Abstract:
Carbon stable isotopes as a palaeoclimate proxy in vascular plant dominated peatlands
© 2015. Carbon stable isotope (δ13C) records from vascular plant dominated peatlands have been used as a palaeoclimate proxy, but a better empirical understanding of fractionation processes in these ecosystems is required. Here, we test the potential of δ13C analysis of ombrotrophic restiad peatlands in New Zealand, dominated by the wire rush (Empodisma spp.), to provide a methodology for developing palaeoclimatic records. We took surface plant samples alongside measurements of water table depth and (micro)climate over spatial (six sites spanning>10° latitude) and temporal (monthly measurements over 1year) gradients and analysed the relationships between cellulose δ13C values and environmental parameters. We found strong, significant negative correlations between δ13C and temperature, photosynthetically active radiation and growing degree days above 0°C. No significant relationships were observed between δ13C and precipitation, relative humidity, soil moisture or water table depth, suggesting no growing season water limitation and a decoupling of the expected link between δ13C in vascular plants and hydrological variables. δ13C of Empodisma spp. roots may therefore provide a valuable temperature proxy in a climatically sensitive region, but further physiological and sub-fossil calibration studies are required to fully understand the observed signal.
Abstract.
Xing W, Bao K, Gallego-Sala AV, Charman DJ, Zhang Z, Gao C, Lu X, Wang G (2015). Climate Controls on carbon accumulation in peatlands of Northeast China.
Quaternary Science Reviews,
115, 78-88.
Abstract:
Climate Controls on carbon accumulation in peatlands of Northeast China
Peatlands contain around one third of the global soil carbon (C) and play an important role in the C cycle. In particular, the response of the productivity-decay balance to climate variability is critical for understanding both the past and future global C cycle. Most studies of peatland C dynamics have been carried out on boreal and subarctic peatlands, where climate models predict a greater increase in temperature compared to the global average. Less is known about peatlands at lower latitudes, yet there are significant peatland C stocks in these regions that may be more vulnerable to future climate change because they are closer to the climatic limit of peatland distribution. Northeast China is China's largest wetland region, with extensive peatlands in mountain regions and across the plains. Here, we used core data from 134 peatland sites to quantify the C accumulation rate over different timescales and estimate C storage across northeast China. The results show that the Holocene long-term apparent rate of C accumulation (LORCA) ranged from 5.74 to 129.31 g C m−2 yr−1, with a mean rate of 33.66 g C m−2 yr−1. The total wetland area and C storage within this region is 82,870 km2 and 4.34 Gt C, and about 80% of the C is contained in mountain peatlands. We find that total C accumulated over the last 2000 years is linearly related to photosynthetically active radiation over the growing season, supporting the hypothesis that rates of net primary productivity (NPP) are more important than decomposition rates in determining long-term C accumulation. Although peatlands in northeast China are close to the southern limit of major peatland extent, our data suggest that future warming will lead to greater future C accumulation, as long as moisture balance or cloudiness do not become limiting factors.
Abstract.
Gallego-Sala AV, Charman DJ, Harrison SP, Li G, Prentice IC (2015). Climate-driven expansion of blanket bogs in Britain during the Holocene.
Clim. Past Discuss.,
11, 4811-4832.
Abstract:
Climate-driven expansion of blanket bogs in Britain during the Holocene
Blanket bog occupies approximately 6 % of the area of the UK today. The Holocene expansion of this hyperoceanic biome has previously been explained as a consequence of Neolithic forest clearance. However, the present distribution of blanket bog in Great Britain can be predicted accurately with a simple model (PeatStash) based on summer temperature and moisture index thresholds, and the same model correctly predicts the highly disjunct distribution of blanket bog worldwide. This finding suggests that climate, rather than land-use history, controls blanket-bog distribution in the UK and everywhere else.
We set out to test this hypothesis for blanket bogs in the UK using bioclimate envelope modelling compared with a database of peat initiation age estimates. We used both pollen-based reconstructions and climate model simulations of climate changes between the mid-Holocene (6000 yr BP, 6 ka) and modern climate to drive PeatStash and predict areas of blanket bog. We compiled data on the timing of blanket-bog initiation, based on 228 age determinations at sites where peat directly overlies mineral soil. The model predicts large areas of northern Britain would have had blanket bog by 6000 yr BP, and the area suitable for peat growth extended to the south after this time. A similar pattern is shown by the basal peat ages and new blanket bog appeared over a larger area during the late Holocene, the greatest expansion being in Ireland, Wales and southwest England, as the model predicts. The expansion was driven by a summer cooling of about 2 °C, shown by both pollen-based reconstructions and climate models. The data show early Holocene (pre-Neolithic) blanket-bog initiation at over half of the sites in the core areas of Scotland, and northern England.
The temporal patterns and concurrence of the bioclimate model predictions and initiation data suggest that climate change provides a parsimonious explanation for the early Holocene distribution and later expansion of blanket bogs in the UK, and it is not necessary to invoke anthropogenic activity as a driver of this major landscape change.
Abstract.
Full text.
Charman DJ, Amesbury MJ, Hinchliffe W, Hughes PDM, Mallon G, Blake WH, Daley TJ, Gallego-Sala AV, Mauquoy D (2015). Drivers of Holocene peatland carbon accumulation across a climate gradient in northeastern North America.
Quaternary Science Reviews,
121, 110-119.
Abstract:
Drivers of Holocene peatland carbon accumulation across a climate gradient in northeastern North America
© 2015 the Authors. Peatlands are an important component of the Holocene global carbon (C) cycle and the rate of C sequestration and storage is driven by the balance between net primary productivity and decay. A number of studies now suggest that climate is a key driver of peatland C accumulation at large spatial scales and over long timescales, with warmer conditions associated with higher rates of C accumulation. However, other factors are also likely to play a significant role in determining local carbon accumulation rates and these may modify past, present and future peatland carbon sequestration. Here, we test the importance of climate as a driver of C accumulation, compared with hydrological change, fire, nitrogen content and vegetation type, from records of C accumulation at three sites in northeastern North America, across the N-S climate gradient of raised bog distribution. Radiocarbon age models, bulk density values and %C measurements from each site are used to construct C accumulation histories commencing between 11,200 and 8000cal. years BP. The relationship between C accumulation and environmental variables (past water table depth, fire, peat forming vegetation and nitrogen content) is assessed with linear and multivariate regression analyses. Differences in long-term rates of carbon accumulation between sites support the contention that a warmer climate with longer growing seasons results in faster rates of long-term carbon accumulation. However, mid-late Holocene accumulation rates show divergent trends, decreasing in the north but rising in the south. We hypothesise that sites close to the moisture threshold for raised bog distribution increased their growth rate in response to a cooler climate with lower evapotranspiration in the late Holocene, but net primary productivity declined over the same period in northern areas causing a decrease in C accumulation. There was no clear relationship between C accumulation and hydrological change, vegetation, nitrogen content or fire, but early successional stages of peatland growth had faster rates of C accumulation even though temperatures were probably lower at the time. We conclude that climate is the most important driver of peatland accumulation rates over millennial timescales, but that successional vegetation change is a significant additional influence. Whilst the majority of northern peatlands are likely to increase C accumulation rates under future warmer climates, those at the southern limit of distribution may show reduced rates. However, early succession peatlands that develop under future warming at the northern limits of peatland distribution are likely to have high rates of C accumulation and will compensate for some of the losses elsewhere.
Abstract.
Full text.
Swindles GT, Morris PJ, Mullan D, Watson EJ, Turner E, Roland TP, Amesbury MJ, Kokfelt U, Schoning K, Pratte S, et al (2015). The long-term fate of permafrost peatlands under rapid climate warming.
Scientific Reports,
5Abstract:
The long-term fate of permafrost peatlands under rapid climate warming
Permafrost peatlands contain globally important amounts of soil organic carbon, owing to cold conditions which suppress anaerobic decomposition. However, climate warming and permafrost thaw threaten the stability of this carbon store. The ultimate fate of permafrost peatlands and their carbon stores is unclear because of complex feedbacks between peat accumulation, hydrology and vegetation. Field monitoring campaigns only span the last few decades and therefore provide an incomplete picture of permafrost peatland response to recent rapid warming. Here we use a high-resolution palaeoecological approach to understand the longer-term response of peatlands in contrasting states of permafrost degradation to recent rapid warming. At all sites we identify a drying trend until the late-twentieth century; however, two sites subsequently experienced a rapid shift to wetter conditions as permafrost thawed in response to climatic warming, culminating in collapse of the peat domes. Commonalities between study sites lead us to propose a five-phase model for permafrost peatland response to climatic warming. This model suggests a shared ecohydrological trajectory towards a common end point: inundated Arctic fen. Although carbon accumulation is rapid in such sites, saturated soil conditions are likely to cause elevated methane emissions that have implications for climate-feedback mechanisms.
Abstract.
Full text.
Bohn TJ, Melton JR, Ito A, Kleinen T, Spahni R, Stocker BD, Zhang B, Zhu X, Schroeder R, Glagolev MV, et al (2015). WETCHIMP-WSL: Intercomparison of wetland methane emissions models over West Siberia.
Biogeosciences,
12(11), 3321-3349.
Abstract:
WETCHIMP-WSL: Intercomparison of wetland methane emissions models over West Siberia
© 2015 Author(s). Wetlands are the world's largest natural source of methane, a powerful greenhouse gas. The strong sensitivity of methane emissions to environmental factors such as soil temperature and moisture has led to concerns about potential positive feedbacks to climate change. This risk is particularly relevant at high latitudes, which have experienced pronounced warming and where thawing permafrost could potentially liberate large amounts of labile carbon over the next 100 years. However, global models disagree as to the magnitude and spatial distribution of emissions, due to uncertainties in wetland area and emissions per unit area and a scarcity of in situ observations. Recent intensive field campaigns across the West Siberian Lowland (WSL) make this an ideal region over which to assess the performance of large-scale process-based wetland models in a high-latitude environment. Here we present the results of a follow-up to the Wetland and Wetland CH4 Intercomparison of Models Project (WETCHIMP), focused on the West Siberian Lowland (WETCHIMP-WSL). We assessed 21 models and 5 inversions over this domain in terms of total CH4 emissions, simulated wetland areas, and CH4 fluxes per unit wetland area and compared these results to an intensive in situ CH4 flux data set, several wetland maps, and two satellite surface water products. We found that (a) despite the large scatter of individual estimates, 12-year mean estimates of annual total emissions over the WSL from forward models (5.34 ± 0.54 Tg CH4 yrg'1), inversions (6.06 ± 1.22 Tg CH4 yrg'1), and in situ observations (3.91 ± 1.29 Tg CH4 yrg'1) largely agreed; (b) forward models using surface water products alone to estimate wetland areas suffered from severe biases in CH4 emissions; (c) the interannual time series of models that lacked either soil thermal physics appropriate to the high latitudes or realistic emissions from unsaturated peatlands tended to be dominated by a single environmental driver (inundation or air temperature), unlike those of inversions and more sophisticated forward models; (d) differences in biogeochemical schemes across models had relatively smaller influence over performance; and (e) multiyear or multidecade observational records are crucial for evaluating models' responses to long-term climate change.
Abstract.
Full text.
2014
Swindles GT, Reczuga M, Lamentowicz M, Raby CL, Turner TE, Charman DJ, Gallego-Sala AV, Valderrama E, Williams C, Draper F, et al (2014). Ecology of Testate Amoebae in an Amazonian Peatland and Development of a Transfer Function
for Palaeohydrological Reconstruction.
Microbial Ecology: an international journalAbstract:
Ecology of Testate Amoebae in an Amazonian Peatland and Development of a Transfer Function
for Palaeohydrological Reconstruction
Tropical peatlands represent globally important carbon sinks with a unique biodiversity and are currently threatened by climate change and human activities. It is now imperative that proxy methods are developed to understand the ecohydrological dynamics of these sys- tems and for testing peatland development models. Testate amoebae have been used as environmental indicators in ecological and palaeoecological studies of peatlands, pri- marily in ombrotrophic Sphagnum-dominated peatlands in the mid- and high-latitudes. We present the first ecolog- ical analysis of testate amoebae in a tropical peatland, a nutrient-poor domed bog in western (Peruvian) Amazonia. Litter samples were collected from different hydrological microforms (hummock to pool) along a transect from the edge to the interior of the peatland. We recorded 47 taxa from 21 genera. The most common taxa are Cryptodifflugia oviformis, Euglypha rotunda type, Phryganella acropodia, Pseudodifflugia fulva type and Trinema lineare. One species found only in the southern hemisphere, Argynnia spicata, is present. Arcella spp. Centropyxis aculeata and Lesqueresia spiralis are indicators of pools containing standing water. Canonical correspondence analysis and non-metric multi- dimensional scaling illustrate that water table depth is a significant control on the distribution of testate amoebae, similar to the results from mid- and high-latitudes peat- lands. A transfer function model for water table based on weighted averaging partial least-squares (WAPLS) regres- sion is presented and performs well under cross-validation (r2apparent = 0.76, RMSE = 4.29; r2jack = 0.68, RMSEP = 5.18). The transfer function was applied to a 1-m peat core, and sample-specific reconstruction errors were generated using bootstrapping. The reconstruction generally suggests near-surface water tables over the last 3,000 years, with a shift to drier conditions at c. cal. 1218-1273 AD.
Abstract.
Swindles GT, Reczuga M, Lamentowicz M, Raby CL, Turner TE, Charman DJ, Gallego-Sala A, Valderrama E, Williams C, Draper F, et al (2014). Ecology of Testate Amoebae in an Amazonian Peatland and Development of a Transfer Function for Palaeohydrological Reconstruction.
Microbial Ecology,
68(2), 284-298.
Abstract:
Ecology of Testate Amoebae in an Amazonian Peatland and Development of a Transfer Function for Palaeohydrological Reconstruction
Tropical peatlands represent globally important carbon sinks with a unique biodiversity and are currently threatened by climate change and human activities. It is now imperative that proxy methods are developed to understand the ecohydrological dynamics of these systems and for testing peatland development models. Testate amoebae have been used as environmental indicators in ecological and palaeoecological studies of peatlands, primarily in ombrotrophic Sphagnum-dominated peatlands in the mid- and high-latitudes. We present the first ecological analysis of testate amoebae in a tropical peatland, a nutrient-poor domed bog in western (Peruvian) Amazonia. Litter samples were collected from different hydrological microforms (hummock to pool) along a transect from the edge to the interior of the peatland. We recorded 47 taxa from 21 genera. The most common taxa are Cryptodifflugia oviformis, Euglypha rotunda type, Phryganella acropodia, Pseudodifflugia fulva type and Trinema lineare. One species found only in the southern hemisphere, Argynnia spicata, is present. Arcella spp. Centropyxis aculeata and Lesqueresia spiralis are indicators of pools containing standing water. Canonical correspondence analysis and non-metric multidimensional scaling illustrate that water table depth is a significant control on the distribution of testate amoebae, similar to the results from mid- and high-latitude peatlands. A transfer function model for water table based on weighted averaging partial least-squares (WAPLS) regression is presented and performs well under cross-validation (rapparent = 0.76, RMSE = 4.29; r2jack = 0.68, RMSEP = 5.18). The transfer function was applied to a 1-m peat core, and sample-specific reconstruction errors were generated using bootstrapping. The reconstruction generally suggests near-surface water tables over the last 3,000 years, with a shift to drier conditions at c. cal. 1218-1273 AD. © 2014 Springer Science+Business Media New York.
Abstract.
Full text.
Holmquist JR, MacDonald GM, Gallego-Sala AV (2014). Peatland Initiation, Carbon Accumulation, and 2 ka Depth in the James Bay Lowland and Adjacent Regions.
Arctic, Antarctic, and Alpine Research,
46(1), 19-39.
Abstract:
Peatland Initiation, Carbon Accumulation, and 2 ka Depth in the James Bay Lowland and Adjacent Regions
Peatlands surrounding Hudson and James Bays form the second largest peatland complex in the world and contain major stores of soil carbon (C). This study utilized a transect of eight ombrotrophic peat cores from remote regions of central and northern Ontario to quantify the magnitude and rate of C accumulation since peatland initiation and for the past 2000 calendar years before present (2 ka). These new data were supplemented by 17 millennially resolved chronologies from a literature review covering the Boreal Shield, Hudson Plains, and Taiga Shield bordering Hudson and James Bays. Peatlands initiated in central and northern Ontario by 7.8 ka following deglaciation and isostatic emergence of northern areas to above sea level. Total C accumulated since inception averaged 109.7 ± (std. dev.) 36.2 kg C m–2. Approximately 40% of total soil C has accumulated since 2 ka at an average apparent rate of 20.2 ± 6.9 g C m–2 yr–1. The 2 ka depths correlate significantly and positively with modern gridded climate estimates for mean annual precipitation, mean annual air temperature, growing degree-days > 0 °C, and photosynthetically active radiation integrated over days > 0 °C. There are significantly shallower depths in permafrost peatlands. Vertical peat accumulation was likely constrained by temperature, growing season length, and photosynthetically active radiation over the last 2 ka in the Hudson Bay Lowlands and surrounding regions.
Abstract.
Full text.
2013
Regnier P, Friedlingstein P, Ciais P, Mackenzie FT, Gruber N, Janssens IA, Laruelle GG, Lauerwald R, Luyssaert S, Andersson AJ, et al (2013). Anthropogenic perturbation of the carbon fluxes from land to ocean.
Nature Geoscience,
6(8), 597-607.
Abstract:
Anthropogenic perturbation of the carbon fluxes from land to ocean
A substantial amount of the atmospheric carbon taken up on land through photosynthesis and chemical weathering is transported laterally along the aquatic continuum from upland terrestrial ecosystems to the ocean. So far, global carbon budget estimates have implicitly assumed that the transformation and lateral transport of carbon along this aquatic continuum has remained unchanged since pre-industrial times. A synthesis of published work reveals the magnitude of present-day lateral carbon fluxes from land to ocean, and the extent to which human activities have altered these fluxes. We show that anthropogenic perturbation may have increased the flux of carbon to inland waters by as much as 1.0 Pg C yr -1 since pre-industrial times, mainly owing to enhanced carbon export from soils. Most of this additional carbon input to upstream rivers is either emitted back to the atmosphere as carbon dioxide (∼0.4 Pg C yr -1) or sequestered in sediments (∼0.5 Pg C yr -1) along the continuum of freshwater bodies, estuaries and coastal waters, leaving only a perturbation carbon input of ∼0.1 Pg C yr -1 to the open ocean. According to our analysis, terrestrial ecosystems store ∼0.9 Pg C yr -1 at present, which is in agreement with results from forest inventories but significantly differs from the figure of 1.5 Pg C yr -1 previously estimated when ignoring changes in lateral carbon fluxes. We suggest that carbon fluxes along the land-ocean aquatic continuum need to be included in global carbon dioxide budgets.
Abstract.
Full text.
Charman DJ, Beilman DW, Blaauw M, Booth RK, Brewer S, Chambers FM, Christen JA, Gallego-Sala A, Harrison SP, Hughes PDM, et al (2013). Climate-related changes in peatland carbon accumulation during the last millennium.
Biogeosciences,
10(2), 929-944.
Abstract:
Climate-related changes in peatland carbon accumulation during the last millennium
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. © 2012 Author(s).
Abstract.
Full text.
2012
Gallego-Sala AV, Prentice C (2012). Blanket peat biome endangered by climate change.
Nature Climate ChangeAbstract:
Blanket peat biome endangered by climate change
Blanket bog is a highly distinctive biome restricted to disjunct hyperoceanic regions. It is characterized by a landscape covering of peat broken only by the steepest slopes1. Plant and microbial life are adapted to anoxia, low pH and low nutrient availability. Plant productivity exceeds soil organic matter decomposition, so carbon is sequestered over time. Unique climatic requirements, including high year-round rainfall and low summer temperatures2, make this biome amenable to bioclimatic modelling. However, projections of the fate of peatlands in general, and blanket bogs in particular, under climate change have been contradictory3, 4, 5, 6, 7. Here we use a simple, well-founded global bioclimatic model8, with climate-change projections from seven climate models, to indicate this biome’s fate. We show marked shrinkage of its present bioclimatic space with only a few, restricted areas of persistence. Many blanket bog regions are thus at risk of progressive peat erosion and vegetation changes as a direct consequence of climate change. New areas suitable for blanket bog are also projected, but these are often disjunct from present areas and their location is inconsistently predicted by different climate models.
Abstract.
Full text.
Loisel J, Gallego-Sala AV, Yu Z (2012). Global-scale pattern of peatland Sphagnum growth driven by photosynthetically active radiation and growing season length.
Biogeosciences,
9(7), 2737-2746.
Abstract:
Global-scale pattern of peatland Sphagnum growth driven by photosynthetically active radiation and growing season length
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. © 2012 Author(s). CC Attribution 3.0 License.
Abstract.
Full text.
Leifeld J, Steffens M, Galego-Sala A (2012). Sensitivity of peatland carbon loss to organic matter quality.
Geophysical Research Letters,
39(14), n/a-n/a.
Full text.
2010
Clark JM, Gallego-Sala AV, Allott TEH, Chapman SJ, Farewell T, Freeman C, House JI, Orr HG, Prentice IC, Smith P, et al (2010). Assessing the vulnerability of blanket peat to climate change using an ensemble of statistical bioclimatic envelope models.
Climate Research,
45(1), 131-150.
Abstract:
Assessing the vulnerability of blanket peat to climate change using an ensemble of statistical bioclimatic envelope models
We assessed the vulnerability of blanket peat to climate change in Great Britain using an ensemble of 8 bioclimatic envelope models. We used 4 published models that ranged from simple threshold models, based on total annual precipitation, to Generalised Linear Models (GLMs, based on mean annual temperature). In addition, 4 new models were developed which included measures of water deficit as threshold, classification tree, GLM and generalised additive models (GAM). Models that included measures of both hydrological conditions and maximum temperature provided a better fit to the mapped peat area than models based on hydrological variables alone. Under UKCIP02 projections for high (A1F1) and low (B1) greenhouse gas emission scenarios, 7 out of the 8 models showed a decline in the bioclimatic space associated with blanket peat. Eastern regions (Northumbria, North York Moors, Orkney) were shown to be more vulnerable than higher-altitude, western areas (Highlands, Western Isles and Argyle, Bute and the Trossachs). These results suggest a long-term decline in the distribution of actively growing blanket peat, especially under the high emissions scenario, although it is emphasised that existing peatlands may well persist for decades under a changing climate. Observational data from long-term monitoring and manipulation experiments in combination with process-based models are required to explore the nature and magnitude of climate change impacts on these vulnerable areas more fully. © Inter-Research 2010.
Abstract.
Full text.
Gallego-Sala AV, Clark JM, House JI, Orr HG, Prentice IC, Smith P, Farewell T, Chapman SJ (2010). Bioclimatic envelope model of climate change impacts on blanket peatland distribution in Great Britain.
Climate Research,
45(1), 151-162.
Abstract:
Bioclimatic envelope model of climate change impacts on blanket peatland distribution in Great Britain
Blanket peatlands are rain-fed mires that cover the landscape almost regardless of topography. The geographical extent of this type of peatland is highly sensitive to climate. We applied a global process-based bioclimatic envelope model, PeatStash, to predict the distribution of British blanket peatlands. The model captures the present areal extent (Kappa = 0.77) and is highly sensitive to both temperature and precipitation changes. When the model is run using the UKCIP02 climate projections for the time periods 2011-2040, 2041-2070 and 2071-2100, the geographical distribution of blanket peatlands gradually retreats towards the north and the west. In the UKCIP02 high emissions scenario for 2071-2100, the blanket peatland bioclimatic space is ∼84% smaller than contemporary conditions (1961-1990); only parts of the west of Scotland remain inside this space. Increasing summer temperature is the main driver of the projected changes in areal extent. Simulations using 7 climate model outputs resulted in generally similar patterns of declining aereal extent of the bioclimatic space, although differing in degree. The results presented in this study should be viewed as a first step towards understanding the trends likely to affect the blanket peatland distribution in Great Britain. The eventual fate of existing blanket peatlands left outside their bioclimatic space remains uncertain. © Inter-Research 2010.
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House JI, Orr HG, Clark JM, Gallego-Sala AV, Freeman C, Prentice IC, Smith P (2010). Climate change and the British Uplands: Evidence for decision-making.
Climate Research,
45(1), 3-12.
Abstract:
Climate change and the British Uplands: Evidence for decision-making
We summarise the work of an interdisciplinary network set up to explore the impacts of climate change in the British Uplands. In this CR Special, the contributors present the state of knowledge and this introduction synthesises this knowledge and derives implications for decision makers. The Uplands are valued semi-natural habitats, providing ecosystem services that have historically been taken for granted. For example, peat soils, which are mostly found in the Uplands, contain around 50% of the terrestrial carbon in the UK. Land management continues to be a driver of ecosystem service delivery. Degraded and managed peatlands are subject to erosion and carbon loss with negative impacts on biodiversity, carbon storage and water quality. Climate change is already being experienced in British Uplands and is likely to exacerbate these pressures. Climate envelope models suggest as much as 50% of British Uplands and peatlands will be exposed to climate stress by the end of the 21st century under low and high emissions scenarios. However, process-based models of the response of organic soils to this climate stress do not give a consistent indication of what this will mean for soil carbon: results range from a very slight increase in uptake, through a clear decline, to a net carbon loss. Preserving existing peat stocks is an important climate mitigation strategy, even if new peat stops forming. Preserving upland vegetation cover is a key win-win management strategy that will reduce erosion and loss of soil carbon, and protect a variety of services such as the continued delivery of a high quality water resource. © Inter-Research 2010.
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Clark JM, Billett MF, Coyle M, Croft S, Daniels S, Evans CD, Evans M, Freeman C, Gallego-Sala AV, Heinemeyer A, et al (2010). Model inter-comparison between statistical and dynamic model assessments of the long-term stability of blanket PEAT in great britain (1940-2099).
Climate Research,
45(1), 227-248.
Abstract:
Model inter-comparison between statistical and dynamic model assessments of the long-term stability of blanket PEAT in great britain (1940-2099)
We compared output from 3 dynamic process-based models (DMs: ECOSSE, MILLENNIA and the Durham Carbon Model) and 9 bioclimatic envelope models (BCEMs; including BBOG ensemble and PEATSTASH) ranging from simple threshold to semi-process-based models. Model simulations were run at 4 British peatland sites using historical climate data and climate projections under a medium (A1B) emissions scenario from the 11-RCM (regional climate model) ensemble underpinning UKCP09. The models showed that blanket peatlands are vulnerable to projected climate change; however, predictions varied between models as well as between sites. All BCEMs predicted a shift from presence to absence of a climate associated with blanket peat, where the sites with the lowest total annual precipitation were closest to the presence/absence threshold. DMs showed a more variable response. ECOSSE predicted a decline in net C sink and shift to net C source by the end of this century. The Durham Carbon Model predicted a smaller decline in the net C sink strength, but no shift to net C source. MILLENNIA predicted a slight overall increase in the net C sink. In contrast to the BCEM projections, the DMs predicted that the sites with coolest temperatures and greatest total annual precipitation showed the largest change in carbon sinks. In this model inter-comparison, the greatest variation in model output in response to climate change projections was not between the BCEMs and DMs but between the DMs themselves, because of different approaches to modelling soil organic matter pools and decomposition amongst other processes. The difference in the sign of the response has major implications for future climate feedbacks, climate policy and peatland management. Enhanced data collection, in particular monitoring peatland response to current change, would significantly improve model development and projections of future change. © Inter-Research 2010.
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2009
Nisbet RER, Fisher R, Nimmo RH, Bendall DS, Crill PM, Gallego-Sala AV, Hornibrook ERC, López-Juez E, Lowry D, Nisbet PBR, et al (2009). Emission of methane from plants.
Proceedings of the Royal Society B: Biological Sciences,
276(1660), 1347-1354.
Abstract:
Emission of methane from plants
It has been proposed that plants are capable of producing methane by a novel and unidentified biochemical pathway. Emission of methane with an apparently biological origin was recorded from both whole plants and detached leaves. This was the first report of methanogenesis in an aerobic setting, and was estimated to account for 10-45 per cent of the global methane source. Here, we show that plants do not contain a known biochemical pathway to synthesize methane. However, under high UV stress conditions, there may be spontaneous breakdown of plant material, which releases methane. In addition, plants take up and transpire water containing dissolved methane, leading to the observation that methane is released. Together with a new analysis of global methane levels from satellite retrievals, we conclude that plants are not a major source of the global methane production. © 2009 the Royal Society.
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Nisbet RER, Fisher R, Nimmo RH, Bendall DS, Crill PM, Gallego-Sala AV, Hornibrook ERC, López-Juez E, Lowry D, Nisbet PBR, et al (2009). Emission of methane from plants.
Proc Biol Sci,
276(1660), 1347-1354.
Abstract:
Emission of methane from plants.
It has been proposed that plants are capable of producing methane by a novel and unidentified biochemical pathway. Emission of methane with an apparently biological origin was recorded from both whole plants and detached leaves. This was the first report of methanogenesis in an aerobic setting, and was estimated to account for 10-45 per cent of the global methane source. Here, we show that plants do not contain a known biochemical pathway to synthesize methane. However, under high UV stress conditions, there may be spontaneous breakdown of plant material, which releases methane. In addition, plants take up and transpire water containing dissolved methane, leading to the observation that methane is released. Together with a new analysis of global methane levels from satellite retrievals, we conclude that plants are not a major source of the global methane production.
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Hornibrook ERC, Bowes HL, Culbert A, Gallego-Sala AV (2009). Methanotrophy potential versus methane supply by pore water diffusion in peatlands.
Biogeosciences,
6(8), 1491-1504.
Abstract:
Methanotrophy potential versus methane supply by pore water diffusion in peatlands
Low affinity methanotrophic bacteria consume a significant quantity of methane in wetland soils in the vicinity of plant roots and at the oxic-anoxic interface. Estimates of the efficiency of methanotrophy in peat soils vary widely in part because of differences in approaches employed to quantify methane cycling. High resolution profiles of dissolved methane abundance measured during the summer of 2003 were used to quantity rates of upward methane flux in four peatlands situated in Wales, UK. Aerobic incubations of peat from a minerotrophic and an ombrotrophic mire were used to determine depth distributions of kinetic parameters associated with methane oxidation. The capacity for methanotrophy in a 3 cm thick zone immediately beneath the depth of nil methane abundance in pore water was significantly greater than the rate of upward diffusion of methane in all four peatlands. Rates of methane diffusion in pore water at the minerotrophic peatlands were small (
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Friedlingstein P, Gallego-Sala AV, Blyth EM, Hewer FE, Seneviratne SI, Spessa A, Suntharalingam P, Scholze M (2009). The earth system feedbacks that matter for contemporary climate. In (Ed)
Understanding the Earth System: Global Change Science for Application, 102-128.
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The earth system feedbacks that matter for contemporary climate
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1999
Gallego-Sala AV, Kennedy KM, Chadwick AV, Niemeier D, Becker KD (1999). An EXAFS and computer modelling study of calcium titanite.
RADIATION EFFECTS AND DEFECTS IN SOLIDS,
151(1-4), 13-19.
Author URL.
Gallego-Sala AV, Kennedy KM, Chadwick AV, Niemeier D, Becker KD (1999). EXAFS and computer modelling study of calcium titanite.
Radiation Effects and Defects in Solids,
151(1), 13-19.
Abstract:
EXAFS and computer modelling study of calcium titanite
Calcium titanite CaTiSiO5 undergoes a phase transition at approximately 220 °C. Extended X-ray Absorption Fine Structure (EXAFS) spectra of both calcium and titanium K-edge have been collected and local structural information extracted from them. The results have been compared with the existing XRD data on this material and the agreement is excellent. In particular, there is good agreement on the changes in bond lengths that occur at the phase transition. A complementary computer simulation study has also been performed and defect formation energies have been calculated.
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