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Task 3 - Biogeochemical cycle of metals in permafrost thaw lakes: inventory of phases, species & reactions
Task 3a - Partner in charge: Oleg Pokrovsky (GET-Toulouse, partner 3)
Major and trace element concentrations in lake ecosystems (O. Pokrovsky; L. Shirokova, S.
Audry; R. Pienitz; post-docs; PhD students; partners engineers)
This sub-task is devoted to acquire a solid chemical data base for all the studied thermokarst lakes. In the
different samples retrieved from the eco-geosystems a number of major (Si, Al, Fe, Ti, Mn, Ca, Mg, Na,
K, P, S, C, N, Cl) and trace elements (alkaline, alkaline earth, rare earth, transition & heavy metals...).
Current analytical methods will be used (elemental analyzers, atomic absorption and emission
spectrometry, mass spectrometry, ...) available in partner 2 and 3 labs as well as at CNRS National
analytical facilities. We estimate that more that 500 samples will be analyzed over the 4 years of the
project. Another goal of this sub-task is to determine sedimentation rates in the studied lakes by using
tracers like 210Pb and 137Cs (14C if necessary) in order to have a temporal perspective of metal enrichments
in the ecosystems. Paleo-ecology data like diatom assemblages will be retrieved from core sediments in
order to document the bio-diversity evolution of the lakes in relation to that of metal contents. Dissolved
oxygen contents, pH, total suspended solids, dissolved organic carbon (DOC), chlorophyll a, bacterial
abundance and temperature along water depth will also be measured. Interpretations will be in terms of
chemical fluxes between reservoirs of the ecosystems, including the atmosphere, and variations of these
fluxes through time using the lake sediments as archives.
Risks: no major risk is identified here. Possible high uncertainties on sedimentation rates.