Litho- and palynostratigraphy at Lobsigensee: Evidences for trophic changes during the Holocene

In the pond of Lobsigensee (2 ha, on the Swiss Plateau) lithostratigraphic and palynostratigraphic units for the Late-glacial and the Holocene have been described. During the Late-Glacial the sediment types are mainly controlled by climate (the end of clay deposition coincides with the end of the Oldest Dryas, i.e. with reforestation at the beginning of Bölling) or by facies (lake marl in the littoral, gyttja in the profundal during Bölling and Alleröd). During the Holocene the facies and the changes in the trophic status, partly combined with water level changes, seem to determine the types of sediment. Two phases of natural eutrophication are deduced from laminated sections during the Boreal and the early Older Atlantic. Towards the end of the Younger Atlantic an early example of a probably anthropogenic eutrophication is found in the layers contemporaneous with the neolithic settlement of the Cortaillod culture. Since the Roman colonization the amount of erosional input has markedly increased.