THE SEPARATION OF THE INFLUENCE OF NUTRIENTS AND CLIMATE ON THE VARVETIME-SERIES OF BALDEGGERSEE, SWITZERLAND

The varve data-set from a freeze-core taken in the deepest part of Bal deggersee was subjected to different multivariate statistical analyses in order to estimate the amount of variance in the varve thickness me asures explicable by past climate and by the trophic state of the lake . A comparison of two different time-periods (1902 to 1992 versus 1920 to 1980) revealed that the lake restoration programme since 1982 has had a significant impact on the formation of the seasonal layers. Resu lts of the partitioning of the variance in the varve thickness measure s showed that about two thirds of the variance are unexplained by a cl imate and trophic state model and that trophic state explains 6%, wher eas climate accounts for about 28% of the variance before the effect o f lake restoration had a strong impact on the varves. Among the climat e parameters the amount of annual precipitation is a strong predictor for explaining the thickness of both dark layer and total couplet thic kness, whereas summer precipitation is important for the thickness of the light layer.