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Mitchell, Edward

Nom
Mitchell, Edward
Affiliation principale
Site web
Fonction
Professeur ordinaire
Email
edward.mitchell@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/357
_
0000-0003-0358-506X

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  • Publication
    Accès libre
    A near-annual palaeohydrological study based on testate amoebae from a sub-alpine mire: surface wetness and the role of climate during the instrumental period
    (2009)
    Lamentowicz, Mariucz
    ;
    van Der Knaap, Willem
    ;
    Lamentowicz, Lukasz
    ;
    van Leeuwen, Jacqueline F. N.
    ;
    Mitchell, Edward 
    ;
    Tomasz, Goslar
    ;
    Kamenik, Christian
    We present the first testate amoeba-based palaeohydrological reconstruction from the Swiss Alps, and the first depth to the water table (DWT) calibration dataset for this region. Compared to existing models, our new calibration dataset performs well (RMSEP = 4.88), despite the length of the water table gradient covered (53 cm). The present-day topography and vegetation of the study mire Mauntschas suggest that it is partly ombrotrophic (large Sphagnum fuscum hummocks, one of which was the coring site) but mostly under the minerotrophic influence of springs in the mire and runoff from the surrounding area. Ombrotrophic Sphagnum fuscum hummocks developed at the sampling site only during the last 50 years, when testate amoebae indicate a shift towards dry and/or acid conditions. Prior to AD 1950 the water table was much higher, suggesting that the influence of the mineral-rich water prevented the development of ombrotrophic hummocks. The reconstructed DWT correlated with Pinus cembra pollen accumulation rates, suggesting that testate amoebae living on the mire and P. cembra growing outside of it partly respond to the same factor(s). Finally, temperature trends from the nearby meteorological station paralleled trends in reconstructed DWT. However, contrary to other studies made on raised bogs of northwestern Europe, the highest correlation was observed for winter temperature, despite the fact that testate amoebae would more logically respond to moisture conditions during the growing season. The observed correlation with winter temperature might reflect a control of winter severity on surface moisture during at least the first part of the growing season, through snow melt and soil frost phenomena influencing run-off. More ecohydrological work on sub-alpine mires is needed to understand the relationships between climate, testate amoebae and peatland development.
  • Publication
    Accès libre
    Palaeoecological evidence for anthropogenic acidification of a kettle-hole peatland in northern Poland
    (2007)
    Lamentowicz, Mariucz
    ;
    Tobolski, Kazimierz
    ;
    Mitchell, Edward 
    The Holocene developmental history of a small kettle-hole peatland in northern Poland was studied using radiocarbon dating and analyses of pollen, plant macrofossils and testate amoebae with the aim of sorting out the influences of climate change, autogenic succession and human impact. The mire followed the classical succession from lake to a Sphagnum-dominated peatland, but peat accumulation only started about 3000 cal. BP. A rapid shift to wetter conditions, lower pH and higher peat accumulation rate took place about 110—150 years before present, when the vegetation shifted to a Sphagnum-dominated poor fen with some bog plants. While the first shift to a peat-accumulating system was most likely driven by climate, the second one was probably caused by forest clearance around the mire. This shift towards a Sphagnum-dominated vegetation mirrors both in pattern and timing the changes observed in similar situations in North America and New Zealand. While human activities have overall caused the loss of vast expanses of peatlands worldwide in recent centuries, locally they may have also allowed the development of communities that are now ironically considered to have a high conservation value. However, in the case of the site studied the likely anthropogenic shift to bog vegetation was at the expense of a species-rich poor fen, which today has even higher conservation value than ombrotrophic bogs. Thus this study also illustrates the value of palaeoecology for peatland management and biodiversity conservation.
  • Publication
    Accès libre
    Testate amoebae (Protists) as palaeoenvironmental indicators in peatlands
    (2005)
    Lamentowicz, Mariusz
    ;
    Mitchell, Edward 
    Testate amoebae (or testaceans, Testacea, Arcellaceans) are unicellular eukaryotic organisms living in freshwater or most terrestrial habitats such as soils, mosses, lakes, rivers, as well as brackish habitats such as estuaries. They are very abundant in Sphagnum mosses, where they live in the top part of mosses and the oxygenated part of the peat. The tests (shells) of Tesiacea are well preserved in peat and to a lesser extent in lake sediments. Efforts should be concentrated on constructing reliable regional transfer functions (mathematical representation of relation of species to environmental variables — presence of particular taxa in fossil material is the function of past environmental pa- rameters). as they exist for some world areas, and there is a complete lack of them for central Europe. Polish data are ex- ceptionally important because Poland is under several contrasted climatic influences — from oceanic to continental. The comparison of our data on climatic tendencies with those from Western Europe and the rest of the world will show how similar or different the responses of Polish peatlands might be. The paper has three aims: (a) to present the need for ecological studies on testate amoebae in Central Europe, (b) to show the potential of reconstruction of past environment on the basis ofmultiproxy studies that include testate amoebae as an in- tegral part of the palaeoecology toolbox and (c) to put our research efforts on testate amoebae in Poland in a more global perspective.