The plight of Amazonia's oldest peatland

Peatlands are globally important ecosystems in terms of biodiversity, hydrology, and for the role they play in the carbon cycle. They store approximately one‐third of the carbon contained in the terrestrial biosphere, whilst covering only approximately 3% of the land and freshwater surface. Tropical peatlands represent an important component of this carbon store and can be found in Asia, Africa, South and Central America. However, tropical peatlands are also under severe threat of destruction from human activities including deforestation, agricultural expansion and resource exploitation. In South America, the Pastaza–Marañon foreland basin (PMFB) in NW Peru represents the most carbon dense landscape in Amazonia due to an abundance of peatlands, including nutrient‐poor ombrotrophic peat domes and river‐influenced minerotrophic swamps. The Aucayacu peatland in the PMFB is a nutrient‐poor peat dome and represents the oldest peatland yet reported in Amazonia. It is a relatively large peatland—it is estimated that Aucayacu has maximum dimensions of 33 km (NW‐SE) by 15 km (NE‐SW) (Fig. 1). The flora of the site is characterized by stunted vegetation due to low nutrient status, known as ‘pole’ and ‘dwarf’ forest, which at Aucayacu grows above a patchy understory of grasses and ferns (Fig. 2). Recent research has shown that Aucayacu has laid down peat up to 7.5 m deep in ∼ 8900 years

Unravelling past impacts of climate change and land management on historic peatland development using proxy‐based reconstruction, monitoring data and process modelling

Peatlands represent globally significant soil carbon stores that have been accumulating for millennia under water‐logged conditions. However, deepening water‐table depths (WTD) from climate change or human‐induced drainage could stimulate decomposition resulting in peatlands turning from carbon sinks to carbon sources. Contemporary WTD ranges of testate amoebae (TA) are commonly used to predict past WTD in peatlands using quantitative transfer function models. Here we present, for the first time, a study comparing TA‐based WTD reconstructions to instrumentally‐monitored WTD and hydrological model predictions using the MILLENNIA peatland model to examine past peatland responses to climate change and land management. Although there was very good agreement between monitored and modelled WTD, TA‐reconstructed water table was consistently deeper. Predictions from a larger European TA transfer function data set were wetter, but the overall directional fit to observed WTD was better for a TA transfer function based on data from northern England. We applied a regression‐based offset correction to the reconstructed WTD for the validation period (1931‐2010). We then predicted WTD using available climate records as MILLENNIA model input and compared the offset‐corrected TA reconstruction to MILLENNIA WTD predictions over an extended period (1750‐1931) with available climate reconstructions. Although the comparison revealed striking similarities in predicted overall WTD patterns, particularly for a recent drier period (1965‐1995), there were clear periods when TA‐based WTD predictions underestimated (i.e. drier during 1830‐1930) and overestimated (i.e. wetter during 1760‐1830) past WTD compared to MILLENNIA model predictions. Importantly, simulated grouse moor management scenarios may explain the drier TA WTD predictions, resulting in considerable model predicted carbon losses and reduced methane emissions, mainly due to drainage. This study demonstrates the value of a site‐specific and combined data‐model validation step towards using TA‐derived moisture conditions to understand past climate‐driven peatland development and carbon budgets alongside modelling likely management impacts

Microform-scale variations in peatland permeability and their ecohydrological implications

1. The acrotelm-catotelm model of peatland hydrological and biogeochemical processes posits that the permeability of raised bogs is largely homogenous laterally but varies strongly with depth through the soil profile; uppermost peat layers are highly permeable while deeper layers are, effectively, impermeable. 2. We measured down-core changes in peat permeability, plant macrofossil assemblages, dry bulk density and degree of humification beneath two types of characteristic peatland microform – ridges and hollows – at a raised bog in Wales. Six 1424 C dates were also collected for one hollow and an adjacent ridge. 3. Contrary to the acrotelm-catotelm model, we found that deeper peat can be as highly permeable as near-surface peat and that its permeability can vary by more than an order of magnitude between microforms over horizontal distances of 1-5 metres. 4. Our palaeo-ecological data paint a complicated picture of microform persistence. Some microforms can remain in the same position on a bog for millennia, growing vertically upwards as the bog grows. However, adjacent areas on the bog (< 10 m distant) show switches between microform type over time, indicating a lack of persistence. 5. Synthesis. We suggest that the acrotelm-catotelm model should be used cautiously; spatial variations in peatland permeability do not fit the simple patterns suggested by the model. To understand how peatlands as a whole function both hydrologically and ecologically it is necessary to understand how patterns of peat physical properties and peatland vegetation develop and persist

Big grains go far: Understanding the discrepancy between tephrochronology and satellite infrared measurements of volcanic ash

There is a large discrepancy between the size of volcanic ash particles measured on the ground at least 500 km from their source volcano (known as cryptotephra) and those reported by satellite remote sensing (effective radius of 0.5-9 I1/4m; 95% of particles reff plateaus at around 9 I1/4m. Assuming Mie scattering by dense spheres when interpreting satellite infrared brightness temperature difference (BTD) data puts an upper limit on retrieved particle sizes. If larger, irregularly shaped ash grains can also produce a BTD effect, this will result in further underestimation of grain size, e.g. in coarse ash clouds close to a volcano

Evidence for ecosystem state shifts in Alaskan continuous permafrost peatlands in response to recent warming

Peatlands in continuous permafrost regions represent a globally-important store of organic carbon, the stability of which is thought to be at risk under future climatic warming. To better understand how these ecosystems may change in a warmer future, we use a palaeoenvironmental approach to reconstruct changes in two peatlands near Toolik Lake on Alaska's North Slope (TFS1 and TFS2). We present the first testate amoeba-based reconstructions from peatlands in continuous permafrost, which we use to infer changes in water-table depth and porewater electrical conductivity during the past two millennia. TFS1 likely initiated during a warm period between 0 and 300 CE. Throughout the late-Holocene, both peatlands were minerotrophic fens with low carbon accumulation rates (means of 18.4 and 14.2 g C m−2 yr−1 for cores TFS1 and TFS2 respectively). However, since the end of the Little Ice Age, both fens have undergone a rapid transition towards oligotrophic peatlands, with deeper water tables and increased carbon accumulation rates (means of 59.5 and 48.2 g C m−2 yr−1 for TFS1 and TFS2 respectively). We identify that recent warming has led to these two Alaskan rich fens to transition into poor fens, with greatly enhanced carbon accumulation rates. Our work demonstrates that some Arctic peatlands may become more productive with future regional warming, subsequently increasing their ability to sequester carbon

Ecology of peatland testate amoebae in the Alaskan continuous permafrost zone

Arctic peatlands represent a major global carbon store, but rapid warming poses a threat to their long-term stability. Testate amoebae are sensitive hydrological indicators that offer insight into Holocene environmental change in peatlands. However, in contrast to temperate peatlands, there have only been a few studies into the ecology of testate amoebae and their efficacy as environmental indicators in permafrost peatlands. We present the first study of testate amoeba ecology from peatlands in the continuous permafrost zone, based on samples from across the Alaskan North Slope. Multivariate statistical analyses show that pore water electrical conductivity (EC), a proxy for nutrient status along the ombrotrophic-minerotrophic gradient, is the dominant control on testate amoeba distribution. Water-table depth (WTD) is also a significant control on testate amoeba distribution, but is secondary to EC. We present two new testate amoeba-based transfer functions to reconstruct both EC (TFEC) and WTD (TFWTD), the first for peatlands in the continuous permafrost zone. The transfer functions are based on Weighted Averaging Partial Least Squares (WAPLS) regression and were assessed using leave-one-out (LOO) cross-validation. We find that both transfer functions have good predictive power. TFWTD is the best performing model (R2JACK = 0.84, RMSEPJACK = 6.66 cm), but TFEC also performs well (R2JACK = 0.76, RMSEPJACK = 146 μS cm−1). Our findings are similar to those conducted in peatlands in discontinuous permafrost regions. The new transfer functions open the opportunity for reconstructing the Holocene dynamics of peatlands of the continuous permafrost zone in Alaska, which represent rapidly changing ecosystems

Corrigendum: Solar cycles or random processes? Evaluating solar variability in Holocene climate records

This is the final version of the article. Available from Springer Nature via the DOI in this record.The article to which this is the corrigendum is in ORE at http://hdl.handle.net/10871/21766A coding error in the Monte Carlo procedure for the determination of critical values in running correlation analysis (presented in Supplementary Data S8) has been brought to the attention of the authors.[...

Holocene fire regimes and treeline migration rates in sub-arctic Canada

Holocene climate change resulted in major vegetation reorganization in sub-arctic Canada near modern treeline. However, little is known of the effects of long-term climate change on boreal forest composition and fire regimes below treeline in this region. We present a high-resolution vegetation and fire history from two sites within the modern boreal forest in the central Northwest Territories, Canada, to provide new insight on sub-arctic vegetation response to Holocene climate dynamics and the role of fire in boreal ecosystems. Palynological analysis of sediments retrieved from Waite and Danny's lakes (informal) is used to reconstruct regional vegetation dynamics and boreal fire regimes. The longer Danny's Lake record documents treeline expansion beginning at ca. 7430–7220 cal yr BP. Integration of our new data with previous work shows that treeline expanded between ca. 4050 cal. yr BP and ca. 3840 cal yr BP at a rate of ca. 50 m/yr in response to the 1–2 °C increase in temperature estimated for the Holocene Thermal Maximum. Forest fires were relatively frequent during the early Holocene, before declining in frequency in response to development of cooler and wetter climate conditions associated with the Neoglacial (beginning after ca. 2200–2320 cal yr BP). We document a trend of increasing fire frequency in the 20th century that is correlated with warming at this time. These dynamics south of modern treeline provide insight into factors creating heterogeneity in plant community responses to large-scale climate events in high northern latitudes and suggest that large scale reorganization of boreal vegetation and fire regimes can be expected over the coming decades

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

Pathways for Ecological Change in Canadian High Arctic Wetlands Under Rapid Twentieth Century Warming

We use paleoecological techniques to investigate how Canadian High Arctic wetlands responded to a midtwentieth century increase in growing degree days. We observe an increase in wetness, moss diversity, and carbon accumulation in a polygon mire trough, likely related to ice wedge thaw. Contrastingly, the raised center of the polygon mire showed no clear response. Wet and dry indicator testate amoebae increased concomitantly in a valley fen, possibly relating to greater inundation from snowmelt followed by increasing evapotranspiration. This occurred alongside the appearance of generalist hummock mosses. A coastal fen underwent a shift from sedge to shrub dominance. The valley and coastal fens transitioned from minerogenic to organic‐rich wetlands prior to the growing degree days increase. A subsequent shift to moss dominance in the coastal fen may relate to intensive grazing from Arctic geese. Our findings highlight the complex response of Arctic wetlands to warming and have implications for understanding their future carbon sink potential