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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 multi-proxy, high-resolution record of peatland development and its drivers during the last millennium from the subalpine Swiss Alps
    (2011)
    van der Knaap, W.O.
    ;
    Mariusz Lamentowicz
    ;
    van Leeuwen, J.F.N
    ;
    Hangartner, S.
    ;
    Leuenberger, M.
    ;
    Dmitri Mauquoy
    ;
    Golslar, T.
    ;
    Mitchell, Edward 
    ;
    Kamenikg, C.
    We present a record of peatland development during the last 1000 years from Mauntschas mire in the eastern Swiss Alps (Upper Engadine valley; 1818 m a.s.l.) inferred from testate amoebae (pH and depth to the water table (DWT) reconstructions), stable oxygen isotopes in Sphagnum (δ18O; proxy for water vapour pressure) and carbon isotopes in Sphagnum (δ13C; proxy for mire surface wetness), peat accumulation rates, charcoal (indicating local burning), pollen and spores (proxies for human impact), and plant macrofossils (reflecting local vegetation and trophic state). Past human impact on the local mire conditions was strong but fluctuating during AD 1000–1570 (±50 yr; depth–age model based on 29 14C AMS dates) with local irrigation of nutrient-enriched water and grazing. Human impact was minor AD 1570–1830 (±30 yr) with partial recovery of the local mire vegetation, and it was absent AD 1830 (±30 yr)–present when hummock formation took place. Correlations among DWT, pH, δ13C, and δ18O, carried out both with the raw data and with linear trends removed, suggest that the factors driving peatland development changed over time, since only testate amoeba-based pH and DWT co-varied during all the three aforementioned periods. δ18O correlates with δ13C only in the period AD 1830–present and with DWT only during AD 1570–1830, δ13C correlates with DWT only during AD 1000–1570. Part of this apparent instability among the four time series might be attributed to shifts in the local mire conditions which potentially formed very different (non-analogue) habitats. Lack of analogues, caused, for example, by pre-industrial human impact, might have introduced artefacts in the reconstructions, since those habitats are not well represented in some proxy transfer functions. Human impact was probably the main factor for peatland development, distorting most of the climate signals.
  • Publication
    Accès libre
    Assessing the ecological value of small testate amoebae (<45 μm) in New Zealand peatlands
    McKeown, Michelle M
    ;
    Wilmshurst, Janet M
    ;
    Duckert, Clément
    ;
    Wood, Jamie R
    ;
    Mitchell, Edward 
    Methodological advances are essential for robust ecological research. Quantitative reconstructions of environmental conditions using testate amoebae rely on sound taxonomy. While the taxonomy of large species is relatively well resolved, this is not the case for most small taxa (typically <45 μm long). In New Zealand, peatlands contain a diversity of both cosmopolitan and characteristic large southern endemic taxa, but also have a high abundance of small taxa. The latter are often lumped into morphotypes reducing their value as ecological indicators. In this study, we demonstrate how (a) lumping small taxa versus splitting them into unique types, and (b) including or excluding them from community analysis influenced their ecological inference. We assessed testate amoeba composition in six peat bogs from New Zealand, three that were moderately-to-highly impacted, and three that were non-impacted. Environmental variables were measured at each sampling site and the surface testate amoeba community patterns and community-environment relationships compared. We found a clear division between impacted and non-impacted sites. Several distinct small taxa were more strongly related to water-table depth and conductivity, while the larger taxa were more correlated to pH. These results show that improved taxonomic resolution of small taxa can provide more informed environmental assessment.