Vulnerability of the peatland carbon sink to sea-level rise

PublishedFreshwater peatlands are carbon accumulating ecosystems where primary production exceeds organic matter decomposition rates in the soil, and therefore perform an important sink function in global carbon cycling. Typical peatland plant and microbial communities are adapted to the waterlogged, often acidic and low nutrient conditions that characterise them. Peatlands in coastal locations receive inputs of oceanic base cations that shift conditions from the environmental optimum of these communities altering the carbon balance. Blanket bogs are one such type of peatlands occurring in hyperoceanic regions. Using a blanket bog to coastal marsh transect in Northwest Scotland we assess the impacts of salt intrusion on carbon accumulation rates. A threshold concentration of salt input, caused by inundation, exists corresponding to rapid acidophilic to halophilic plant community change and a carbon accumulation decline. For the first time, we map areas of blanket bog vulnerable to sealevel rise, estimating that this equates to ~7.4% of the total extent and a 0.22 Tg yr−1 carbon sink. Globally, tropical peatlands face the proportionally greatest risk with ~61,000 km2 (~16.6% of total) lying ≤5 m elevation. In total an estimated 20.2 ± 2.5 GtC is stored in peatlands ≤5 m above sea level, which are potentially vulnerable to inundation.We wish to thank Dr. Zicheng Yu at Lehigh University for providing the map of global peatlands, and Dr. Damien Mansell (University of Exeter) who helped with data processing. Our thanks also go to Dr. Lisa Orme and Nicole Sanderson for laboratory support with 210Pb dating, and to Scottish Natural Heritage for arranging access to the site. We thank Howard Bowman for insightful comments on the initial manuscript draft. We are also grateful to the Natural Environment Research Council (NERC grant number NE/I012915/1) for the funding to support the work presented in this article

Methanotrophy potential versus methane supply by pore water diffusion in peatlands

Journal ArticlePublished by Copernicus Publications on behalf of the European Geosciences UnionAuthor(s) 2009.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 (<10%) compared to surface emissions during June to August. The proportions were notably greater in the ombrotrophic bogs because of their typically low methane emission rates. Methanotrophy appears to consume entirely methane transported by pore water diffusion in the four peatlands with the exception of 4 of the 33 gas profiles sampled. Flux rates to the atmosphere regardless are high because of gas transport through vascular plants, in particular, at the minerotrophic sites. Cumulative rainfall amount 3-days prior to sampling correlated well with the distance between the water table level and the depth of 0 μmol l-1 methane, indicating that precipitation events can impact methane distributions in pore water. Further work is needed to characterise the kinetics of methane oxidation spatially and temporally in different wetland types in order to determine generalized relationships for methanotrophy in peatlands that can be incorporated into process-based models of methane cycling in peat soils.Natural Environment Research Council (NERC)Royal Societ

Ecological resilience of restored peatlands to climate change

This is the final version. Available from Nature Research via the DOI in this record. Degradation of peatlands through land-use change and drainage is currently responsible for 5-10% of global annual anthropogenic carbon dioxide emissions. Therefore, restoring disturbed and degraded peatlands is an emerging priority in efforts to mitigate climate change. While restoration can revive multiple ecosystem functions, including carbon storage, the resilience of restored peatlands to climate change and other disturbances remains poorly understood. Here, we review the recent literature on the response of degraded and restored peatlands to fire, drought and flood. We find that degraded sites can generally be restored in a way that allows for net carbon sequestration. However, biodiversity, hydrological regime, and peat soil structure are not always fully restored, even after a decade of restoration efforts, potentially weakening ecosystem resilience to future disturbances. As the recovery of degraded peatlands is fundamental to achieving net-zero goals and biodiversity targets, sound science and monitoring efforts are needed to further inform restoration investments and priorities

Methanotrophy potential versus methane supply by pore water diffusion in peatlands

International audienceLow 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 quantify rates of upward methane flux in four peatlands situated in Wales, UK. Aerobic incubations of peat from a minerotrophic and an ombrogenous 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 (?mol l?1 methane, indicating that precipitation events can impact methane distributions in pore water. Further work is needed to characterise the kinetics of methane oxidation spatially and temporally in different wetland types in order to determine generalized relationships for methanotrophy in peatlands that can be incorporated into process-based models of methane cycling in peat soils

Salt-Enrichment Impact on Biomass Production in a Natural Population of Peatland Dwelling Arcellinida and Euglyphida (Testate Amoebae)

This is the final version. Available on open access from Springer Verlag via the DOI in this recordUnicellular 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.Natural Environment Research Council (NERC

Low-salinity transitions drive abrupt microbial response to sea-level change

This is the final version. Available on open access from Wiley via the DOI in this recordData availability statement: Authors have data permissions for all data used in this study. Data deriving from published sources are referenced in the manuscript. The datasets used in this study are available from the British Antarctic Survey Polar Data Centre, and the figshare repository (https://doi.org/10.6084/m9.figshare.16573346.v1).The salinisation of many coastal ecosystems is underway and is expected to continue into the future because of sea-level rise and storm intensification brought about by the changing climate. However, the response of soil microbes to increasing salinity conditions within coastal environments is poorly understood, despite their importance for nutrient cascading, carbon sequestration and wider ecosystem functioning. Here, we demonstrate deterioration in the productivity of a top-tier microbial group (testate amoebae) with increasing coastal salinity, which we show to be consistent across phylogenetic groups, salinity gradients, environment types and latitude. Our results show that microbial changes occur in the very early stages of marine inundation, presaging more radical changes in soil and ecosystem function and providing an early warning of coastal salinisation that could be used to improve coastal planning and adaptation.Natural Environment Research Council (NERC)Sécurité publique du QuébecUniversity of Exete

Seasonal climate drivers of peak NDVI in a series of Arctic peatlands

This is the final version. Available from Elsevier via the DOI in this record. Changes in plant cover and productivity are important in driving Arctic soil carbon dynamics and sequestration, especially in peatlands. Warming trends in the Arctic are known to have resulted in changes in plant productivity, extent and community composition, but more data are still needed to improve understanding of the complex controls and processes involved. Here we assess plant productivity response to climate variability between 1985 and 2020 by comparing peak growing season NDVI (Normalised Difference Vegetation Index data from Landsat 5 and 7), to seasonal-average weather data (temperature, precipitation and snow-melt timing) in nine locations containing peatlands in high- and low-Arctic regions in Europe and Canada. We find that spring (correlation 0.36 for peat dominant and 0.39 for mosaic; MLR coefficient 0.20 for peat, 0.29 for mosaic), summer (0.47, 0.42; 0.18, 0.17) and preceding-autumn (0.35, 0.25; 0.33, 0.27) temperature are linked to peak growing season NDVI at our sites between 1985 and 2020, whilst spring snow melt timing (0.42, 0.45; 0.25, 0.32) is also important, and growing season water availability is likely site-specific. According to regression trees, a warm preceding autumn (September-October-November) is more important than a warm summer (June-July-August) in predicting the highest peak season productivity in the peat-dominated areas. Mechanisms linked to soil processes may explain the importance of previous-Autumn conditions on productivity. We further find that peak productivity increases in these Arctic peatlands are comparable to those in the surrounding non-peatland-dominant vegetation. Increased productivity in and around Arctic peatlands suggests a potential to increased soil carbon sequestration with future warming, but further work is needed to test whether this is evident in observations of recent peat accumulation and extent.Natural Environment Research Council (NERC

Holocene atmospheric dust deposition in NW Spain

This is the author accepted manuscript. The final version is available from SAGE Publications via the DOI in this record.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.Natural Environment Research Council (NERC)Consiliencia networkFunding for Consolidation and Structuration of Research Unit

The tropical peatland archaeal lipidome – influence of vegetation and redox on diversity

This is the final version. Available from the European Association of Geoscientists & Engineers via the DOI in this record. The nature, variability, and diversity of environmental microbiomes and lipidomes are vital to understanding soil health, biogeochemical processes and reconstructing past climates. Such research on peatlands – especially tropical peatlands – is limited, despite their importance to the global carbon cycle through the sequestration of organic matter (OM) and production of methane. Here, we explore the distribution of archaea and their isoprenoidal glycerol dialkyl glycerol tetraether lipids (isoGDGTs) across a range of wetlands, in order to ascertain the controls on their distribution. We focus specifically on vegetation and OM composition to explore the relationships between archaeal ecology and carbon cycling in tropical contexts. Through international collaboration, we created a database of core archaeal and bacteria lipid distributions of hundreds of peats from globally widespread sites (the TGRES Peat Database, Naafs et al., 2017). This formed the basis for peat-specific temperature and pH proxies based on the distribution of bacterial branched GDGTs as initially pioneered for mineral soils. However, clear environmental controls and patterns in the distribution of archaeal lipids are ambiguous (Naafs et al., 2018). For example, isoGDGT-5 is restricted to high temperature and low pH settings, but other isoGDGT and overly methylated isoprenoidal GDGT (Me-GDGTs) ring indices are poorly correlated with temperature and pH (Blewett et al., 2020). This suggests that in comparison to previously established GDGT-based environmental proxies the archaeal GDGTs of peatlands derive from an ecologically diverse group of organisms that confound simple environmental comparisons. Given the increased recognition of archaeal metabolic diversity, including a range of heterotrophic, methanotrophic and methanogen ecologies, it seems likely that changes in vegetation, peat OM composition and water level depth will impose significant controls on the archaeal community – and that of the lipids they produce

Shifts in national land use and food production in Great Britain after a climate tipping point

This is the author accepted manuscript. The final version is available from Nature Research via the DOI in this recordData availability: The modelled output data that support the findings of this study are openly available from: Smith, G. S. & Ritchie, P. D. L. (NERC Environmental Information Data Centre: 639 doi.org/10.5285/e1c1dbcf-2f37-429b-af19-a730f98600f6, 2019).Climate change is expected to impact agricultural land use. Steadily accumulating changes in temperature and water availability can alter the relative profitability of different farming activities and promote land use changes. There is also potential for high-impact ‘climate tipping points’ where abrupt, non-linear change in climate occurs - such as the potential collapse of the Atlantic Meridional Overturning Circulation (AMOC). Here, using data from Great Britain, we develop a methodology to analyse the impacts of a climate tipping point on land use and economic outcomes for agriculture. We show that economic/land use impacts of such a tipping point are likely to include widespread cessation of arable farming with losses of agricultural output, an order of magnitude larger than the impacts of climate change without an AMOC collapse. The agricultural effects of AMOC collapse could be ameliorated by technological adaptations such as widespread irrigation, but the amount of water required and the costs appear prohibitive in this instance.Natural Environment Research Council (NERC)Alan Turing Institut