High resolution analysis of fossil pigments, carbon, nitrogen and sulphur in the sediment of eight European Alpine lakes: the MOLAR project

A palaeoenvironmental reconstruction for the past 2-3 centuries of eight remote sites from northern to southern Europe was based on a number of palaeolimnological proxies, especially fossil pigments. Most of the lakes studied are located above the timberline and a great effort centred on the creation and analysis of a data-sets of sedimentary records. A chronology for the last century was based on radiometric techniques (210Pb, 241Am 137Cs). The accumulation rate of recent sediment was found to vary from 0.041 cm y-1 (Lake Saanajarvi, Finland) to 0.14 cm y-1 (Jezero v Ledvici, Slovenia). During the time-span represented by the cores were the major changes in organic carbon and nitrogen in Nižne Terianske Pleso (Slovakia), Redo (Spain) and Gossenkollesee (Austria). Constant increase of these nutrients from AD 1900 onwards was shown in lakes Saanajarvi, Nižne Terianske Pleso and Hagelseewli (Switzerland). No common trends in sulphur concentrations was evident. There is evidence of an atmospheric input of sulphur in Hagelseewli. This lake shows the highest concentrations, 10 fold higher at surface than the other lakes (ca 6% d.m.). A decrease of S during very recent times is clearly shown by the cores from Redo and Hagelseewli: this might be related to the reduction in the atmospheric loading (the matching of the atmospheric and sedimentary sulphur trends favours this hypothesis). Concentrations of total pigments and HPLC single carotenoids and chlorophylls showed marked fluctuations throughout the cores of all lakes. High pre-AD 1800 pigment concentrations were detected in Nižne Terianske Pleso, Redo, Hagelseewli and Gossenkollesee. During the last ca 50 years an increase in productivity inferred from fossil pigments is shown by Ovre Neadalsvatn (Norway), Nižne Terianske Pleso, Saanajarvi and Jezero v Ledvici. Except Gossenkollesee (Kamenik et al. 2000, this issue). Significant catchment disturbances are absent in these remote environments, so these increases can be considered to be the result of temperature increase or atmospheric nutrient pollution. Carotenoids belonging to sulphur anaerobic photosynthetic bacteria of the green and red groups (Chlorobiaceae and Chromatiaceae) were found in three lakes, i.e. Jezero v Ledvici, Hagelseewli and Gossenkollesee, implying that these lakes experienced seasonal anoxia in their bottom waters with strong stratification.

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