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 Saanajärvi, 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 Nižné Terianske Pleso (Slovakia), Redó (Spain) and Gossenköllesee (Austria). Constant increase of these nutrients from AD 1900 onwards was shown in lakes Saanajärvi, Nižné 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 Redò 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 Nižné Terianske Pleso, Redó, Hagelseewli and Gossenköllesee. During the last ca 50 years an increase in productivity inferred from fossil pigments is shown by Øvre Neådalsvatn (Norway), Nižné Terianske Pleso, Saanajärvi and Jezero v Ledvici. Except Gossenköllesee (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 Gossenköllesee, implying that these lakes experienced seasonal anoxia in their bottom waters with strong stratification.