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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
    Métadonnées seulement
    Cut-over peatland regeneration assessment using organic matter and microbial indicators (bacteria and testate amoebae)
    (2008)
    Laggoun-Défarge, Fatima
    ;
    Mitchell, Edward 
    ;
    Gilbert, Daniel
    ;
    Disnar, Jean-Robert
    ;
    Comont, Laure
    ;
    Warner, Barry
    ;
    Buttler, Alexandre
    1. Cut-over peatlands cover large surfaces of high potential value for enhancing biodiversity and carbon sequestration if successfully restored. Unfortunately, evaluation of restoration success is not straightforward. We assessed the bioindicator value of organic matter (OM), testate amoebae (protozoa) and bacteria in peat from two regeneration stages and a reference site of a cut-over bog. 2. Contrasting biochemical signatures of peat OM were observed along the regenerating profiles, allowing clear differentiation between the newly regenerated peat and the old peat. Where peat macrofossils were absent sugar biomarkers were used to infer peat botanical origin and OM alteration. 3. Over the succession, the OM composition of the new peat differed. Peat from the more recent stage was dominated by Sphagnum-derived tissues and characterized by lower carbohydrate preservation and higher bacterial biomass than the advanced regeneration stage. 4. Surface testate amoeba communities also changed from the recent to the advanced stages of regeneration, indicating a shift from wet and moderately acidic conditions to drier and more acidic conditions. Over this regeneration sequence (i) the biomass and average size of species declined but were higher at the unexploited site and (ii) species richness and diversity increased but density declined. 5. Synthesis and applications. Although secondary succession in the cut-over bog led to an ecosystem similar to that of the reference site in terms of surface vegetation, OM and testate amoebae continued to reflect disturbances associated with peat harvesting. Nevertheless, the described dynamics of both microbial and biochemical variables over the succession showed similarities between the advanced stage and the reference site: a higher testate amoeba diversity was associated with better carbohydrate preservation and a more heterogeneous botanical composition of the peat. The inferred water table depth and pH based on testate amoebae indicators proved to be an alternative approach for assessing restoration processes, in contrast to labour-intensive repeated measurements in the field. The botanical and biochemical composition of peat OM provided additional information on past anthropogenic perturbations of the bog and could be used for restoration monitoring. The combination of several indicators therefore provides a more complete assessment of ecological conditions that could be valuable for the management of cut-over peatlands.
  • Publication
    Métadonnées seulement
    Contrasted effects of increased N and CO2 supply on two keystone species in peatland restoration and implications for global change
    (2002-5-2)
    Mitchell, Edward 
    ;
    Buttler, Alexandre
    ;
    Grosvernier, Philippe
    ;
    Rydin, Hakan
    ;
    Siegenthaler, Andy
    ;
    Gobat, Jean-Michel 
    1 Significant areas of temperate bogs have been damaged by peat harvesting but may regenerate. These secondary mires, if well managed, may act as strong C sinks, regulate hydrology and buffer regional climate. 2 The potential effects of bog regeneration will, however, depend on the successful establishment of the principal peat formers - Sphagnum mosses. The influence of hydrology and microclimate on Sphagnum re-growth is well studied but effects of elevated CO2 and N deposition are not known. 3 We carried out two in-situ experiments in a cutover bog during three growing seasons in which we raised either CO2 (to 560 p.p.m.) or N (by adding NH4NO3, 3 g m(-2) year(-1)). The two treatments had contrasting effects on competition between the initial coloniser Polytrichum strictum (favoured by high N) and the later coloniser Sphagnum fallax (favoured by high CO2). 4 Such changes may have important consequences for bog regeneration and hence for carbon sequestration in cutover bogs, with potential feedback on regional hydrological and climatic processes.
  • Publication
    Métadonnées seulement
    Effects of elevated CO2 and nitrogen deposition on natural regeneration processes of cut-over ombrotrophic peat bogs in the Swiss Jura mountains
    (: Springer, 1999-5-2)
    Grosvernier, Philippe
    ;
    Mitchell, Edward 
    ;
    Buttler, Alexandre
    ;
    Gobat, Jean-Michel 
    ;
    Visconti, Guido
    ;
    Beniston, Martin
    ;
    Iannorelli, Emilio D
    ;
    Barba, Diego
    In the Swiss Jura mountains most of the remaining ombrotrophic pear bogs have been exploited to some extent for peat. In these sires, natural regeneration processes are taking place. The dominant process is paludification, where a cut over drained surface is colonised by key species, usually either Polytrichum strictum or Eriophortum vaginatum. These early colonisers of bare pear surfaces create microclimatic conditions that enable the re-colonisation of Sphagnum mosses, usually S. fallax. In later stages of the succession S. fallax grows to Form a continuous carpet and the key species gradually suffer from competition for light availability. We studied the effect of elevated CO2 (560 ppm) and nitrogen deposition (30 kg ha(-1) year(-1)) on the competition between Sphagnum fallax and Polytrichum strictum year in a three years field experiment (EU project BERI - Bog Ecosystem Research Initiative) using miniFACE systems (small size Free Air Carbon dioxide Enrichment). The cover and growth in length of the two species was monitored. The height difference between the emerging Polytrichum and the top of the Sphagnum mosses was also recorded at regular intervals, Effect Of CO2: Sphagnum covet increased in the first year but this trend was not confirmed subsequently, whereas Polytrichum cover was not affected by elevated CO2 Both Sphagnum and Polytrichum had a reduced growth in length under elevated CO2. However, the growth of Sphagnum was less reduced than that of Polytrichum and therefore the height difference between Sphagnum and Polytrichum decreased. Effect of N: Sphagnum cover declined and Polytrichum cover doubled over the three years period in the high N plots. Sphagnum growth in length was not significant affected by N, but Polytrichum grew more in the high N plots. As a results the height difference between Sphagnum and Polytrichum increased. These results suggest that elevated CO2 and nitrogen deposition may have contrasting effects on bog regeneration. The positive effect of elevated CO2 on Sphagnum mosses may be counterbalanced by higher N deposition levels.
  • Publication
    Métadonnées seulement
    Ecology of testate amoebae (Protozoa : Rhizopoda) in Sphagnum peatlands in the Jura mountains, Switzerland and France
    (1999-5-2)
    Mitchell, Edward 
    ;
    Buttler, Alexandre
    ;
    Warner, Barry
    ;
    Gobat, Jean-Michel 
    Testate amoebae (Protozoa) living in Sphagnum peatlands are important environmental and paleoecological indicators. The distribution of these animals is closely related to soil moisture variables. This study examines the ecology of sphagnicolous testate amoebae near the southern limit of bogs in Europe. A total of 64 samples were collected for analysis of testate amoebae from six peatlands in the Jura region of Switzerland and France. Eleven site-specific ecological variables, six of which were soil-moisture related variables, were measured at each site. The data were subjected to weighted averaging, jack-knifing, cluster analysis, canonical correspondence analysis, and the indicator value method to model relationships between testate amoebae distributions and environmental variables. Testate amoebae abundance showed a direct relationship with pear pH and depth to water table. Strong relationships were with sites that had a water table less than 41 cm deep. In drier sites with water table depth greater than 41 cm, other factors such as soil porosity and water holding capacity were more important compared to the wetter sites. Though there was a strong relationship between restate amoebae faunas and soil moisture content and porosity, these two variables could not be confidently predicted. Testate amoebae in peatlands in this region appear to be sensitive to peat pH and water tables. Further work is needed to explore relationships between restate amoebae, soil moisture, and porosity.