465 research outputs found
Palaeoecology of testate amoebae in a tropical peatland.
We present the first detailed analysis of subfossil testate amoebae from a tropical peatland. Testate amoebae were analysed in a 4-m peat core from western Amazonia (Peru) and a transfer function developed from the site was applied to reconstruct changes in water table over the past ca. 8,000 years. Testate amoebae were in very low abundance in the core, especially in the lower 125cm, due to a combination of poor preservation and obscuration by other organic matter. A modified preparation method enabled at least 50 testate amoebae to be counted in each core sample. The most abundant taxa preserved include Centropyxis aculeata, Hyalosphenia subflava, Phryganella acropodia and Trigonopyxis arcula. Centropyxis aculeata, an unambiguous wet indicator, is variably present and indicates several phases of near-surface water table. Our work shows that even degraded, low-abundance assemblages of testate amoebae can provide useful information regarding the long-term ecohydrological developmental history of tropical peatlands
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 oneâthird 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 PastazaâMarañon foreland basin (PMFB) in NW Peru represents the most carbon dense landscape in Amazonia due to an abundance of peatlands, including nutrientâpoor ombrotrophic peat domes and riverâinfluenced minerotrophic swamps. The Aucayacu peatland in the PMFB is a nutrientâpoor peat dome and represents the oldest peatland yet reported in Amazonia. It is a relatively large peatlandâit is estimated that Aucayacu has maximum dimensions of 33 km (NWâSE) by 15 km (NEâSW) (Fig. 1). The flora of the site is characterized by stunted vegetation due to low nutrient status, known as âpoleâ and âdwarfâ 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
The presence of Holocene cryptotephra in Wales and southern England
There have been few detailed studies into the tephrostratigraphy of southern Britain. We report the tephrostratigraphy of two sites, one in southern England (Rough Tor, Cornwall) and one in Wales (Cors Fochno, west Wales). Our study extends the known southernmost reach of Icelandic cryptotephra in northern Europe. Given the large distance between sites in southern England and eruptive sources (e.g. Iceland 1500â1700âkm distant), most of the cryptotephra layers consist of sparse numbers of shards, even by the standards of distal tephrostratigraphy (as low as 3 shards cmâ1), each layer spanning only 1 or 2âcm in depth. We identify multiple cryptotephra layers in both sites, extending the known distribution of several tephra layers including the MOR-T4 tephra (âŒAD 1000) most probably of Icelandic origin, and the AD 860 B tephra correlated to an eruption of Mount Churchill, Alaska. The two sites record contrasting tephrostratigraphies, illustrating the need for the inclusion of multiple sites in the construction of a regional tephrostratigraphic framework. The tephra layers we describe may provide important isochrons for the dating and correlation of palaeoenvironmental sequences in the south of Britain
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 â ridges
and hollows â 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
Coring and sub-sampling of peatlands for palaeoenvironmental research
Every palaeoenvironmental, palaeoecological and palaeogeochemical study of a peatland begins with coring or section sampling and sub-sampling. This first step in a peat-based palaeoenvironmental study is the most crucial, as a high-quality investigation can be achieved only from a foundation of high-quality stratigraphic sampling and sub-sampling. Various techniques for coring, sampling and sub-sampling are described, aiming to: (a) provide the reader with an overview of existing approaches and techniques; (b) offer guidance on good practice for achieving high-quality results efficiently; and (c) standardise the methodology in order to achieve comparable sequences and samples for future multiproxy, multi-site and multi-core projects
Testing peatland water-table depth transfer functions using high-resolution hydrological monitoring data
Transfer functions are now commonly used to reconstruct past environmental variability from palaeoecological data. However, such approaches need to be critically appraised. Testate amoeba-based transfer functions are an established method for the quantitative reconstruction of past water-table variations in peatlands, and have been applied to research questions in palaeoclimatology, peatland ecohydrology and archaeology. We analysed automatically-logged peatland water-table data from dipwells located in England, Wales and Finland and a suite of three year, one year and summer water-table statistics were calculated from each location. Surface moss samples were extracted from beside each dipwell and the testate amoebae community composition was determined. Two published transfer functions were applied to the testate-amoeba data for prediction of water-table depth (England and Europe). Our results show that estimated water-table depths based on the testate amoeba community reflect directional changes, but that they are poor representations of the real mean or median water-table magnitudes for the study sites. We suggest that although testate amoeba-based reconstructions can be used to identify past shifts in peat hydrology, they cannot currently be used to establish precise hydrological baselines such as those needed to inform management and restoration of peatlands. One approach to avoid confusion with contemporary water-table determinations is to use residuals or standardised values for peatland water-table reconstructions. We contend that our test of transfer functions against independent instrumental data sets may be more powerful than relying on statistical testing alone
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
Unravelling past impacts of climate change and land management on historic peatland development using proxyâbased reconstruction, monitoring data and process modelling
Peatlands represent globally significant soil carbon stores that have been accumulating for millennia under waterâlogged conditions. However, deepening waterâtable depths (WTD) from climate change or humanâinduced 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 TAâbased WTD reconstructions to instrumentallyâmonitored 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, TAâreconstructed 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 regressionâbased offset correction to the reconstructed WTD for the validation period (1931â2010). We then predicted WTD using available climate records as MILLENNIA model input and compared the offsetâcorrected TA reconstruction to MILLENNIA WTD predictions over an extended period (1750â1931) with available climate reconstructions. Although the comparison revealed striking similarities in predicted overall WTD patterns, particularly for a recent drier period (1965â1995), there were clear periods when TAâbased WTD predictions underestimated (i.e. drier during 1830â1930) and overestimated (i.e. wetter during 1760â1830) 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 siteâspecific and combined dataâmodel validation step towards using TAâderived moisture conditions to understand past climateâdriven peatland development and carbon budgets alongside modelling likely management impacts
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 14.2âŻgâŻC mâ2 yrâ1 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 48.2âŻgâŻC mâ2 yrâ1 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
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