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Lake Muggelsee and its Environment -Natural Conditions and Anthropogenic Impacts key words: lake characteristics (geology. hydrology, morphometry, history, usage, water quality, fauna and flora) Abstract Lake Muggelsee, a polymictic eutrophic lake at the eastern border of the city of Berlin (area: 7.3 km2, mean depth: 4.9 m) is e y influenced by the River Spree (flowing through the lake) and subject to various usages, especially to municipal water supply and recreation. Geomorphologic development, morphometric features, climatic conditions, hydrological regime, and position in the hydrographic net are described. Short information is given on fauna and flora of the lake, and on characteristics of the catchment area. Water quality parameters are summarized as 12 year average (1979-1990) and the eutrophic state is compared to other lakes. Finally, a short report on scientific research activities is given.

The atmospheric production rate of the cosmogenic isotope 10Be is modulated by the solar wind. Spectral analysis of a 560 year long 10Be concentration record from a Greenland ice core shows that this modulation process was active at all times even during quiet sun periods (Maunder minimum). To separate production effects from the effects of transport and deposition processes, three 10Be records of different length and time resolution were used to calculate the expected 14C variations.Comparisons with measured 14C variations show that during the Holocene, for time scales larger than 3 years, the mixing and transport processes played only a minor role. Measurements of these isotopes in terrestrial archives therefore provide information about past solar variability.Satellite measurements reveal a positive relationship between solar activity and solar irradiance. Comparisons between 10Be in polar ice samples and 14C in tree rings with temperature records show common features which confirm this relationship over the last few centuries.

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