Partenaires et organisations internationales
(Anglais)
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ENSCMu Mulhouse(F), ULP Strasbourg (F), FBG Barcelona (E), EAWAG Dübendorf (CH), UCL London (GB)
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Résumé des résultats (Abstract)
(Anglais)
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Lake sediments of 8 lakes were analysed downcore for phospholipid fatty acids (PLFA).
PLFA, which are unstable outside of living cells, were found also in the deeper parts of the sediments. This indicates that microorganisms are still alive, probabely as resting cells or spores. Consequently the trapped cell constituents, like PLFA, are not subjected to degradation processes and may reflect the PLFA composition of microbial sediment communities grown on former sediment surfaces. The distribution of PLFA downcore and the correlation of major compositional changes with known eutrophication steps strongly support this hypothesis.
Further, the PLFA data was compared with the results of fossil lipid, fossil diatom, fossil cladoceran and ostracodes analyses of the same sediment layers. PLFA inferred values and fossil inferred values show interpretable correspondences. It was shown that the divers analyses enable the reconstruction of
· microbial communities, with the subgroups eucariotic algae, fungi, protozoa, cyanobacteria, bacteria, proteobacteria alpha, proteobacteria gamma and beta, actinomycetes, methylotrophic bacteria, lactic acid bacteria, sulfate reducing bacteria and others
· diatom communities
· phytoplancton structure
· parts of zooplancton communities
· and eutrophication forced changes in key groups of the lake community.
Thus, it is evident that PLFA analyses offer monitoring and reconstruction tools for the microbial part of lakes biodiversity. Further, combined analyses (geochemical, molecular, fossils) may enable an integrated, ecological reconstruction of lake history and assessment of lake quality.
From the results so far, several general conclusions of broader importance can be drawn. Lakes are mirrors and archives of the changes in the catchment area. BIOMASS showed that the combination of geochemical, molecular and microfossil analyses extends the scope and use of paleolimnological reconstructions. Hypothese about the effects of man made chemicals, changes in land use and shifts in biological traits of organisms in the environment may be tested and tools for the integrated assessment of lake quality and catchment area quality may be developped. Finally, the isolation and reactivation of burried microorganisms seems to be possible at least on an age scale of one hundred years.
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