Lake Lucerne, Switzerland, a long term study of 1961-1992

Lake Lucerne. Switzerland. "Kreuztrichter"-basin, was investigated between 1961 and 1992. This time period offered a unique opportunity to study an eutrophication event lasting some ten years and the following recovery period as well as the limnological behavior of a deep pre-alpine lake. Results are presented as isopleths and long-term trends. Five year averages show clear patterns in the dynamics of ammonia or nitrite. Lake Lucerne (Kastanienbaum basin) is a monomictic lake. with only one complete overturn every six years. Other basins of Lake Lucerne such as the southernmost basin (Lake Uri), destratify each year, because of its wind-channel orientation. Kreuztrichter Basin was physically stabilized for years by trophic-induced processes. As the take recovered. the density gradient in the bottom water layer decreased and turnover frequency increases. The oxygen peak in summer was usually overridden by temperature effects. Nitrogen concentration increased steadily during the 30 year period. Data for N, P, Si and O-2 suggested the concept of compensation depth could be applied. The results were e. g. settling seston had no effect on nitrogen but caused a decrease in soluble phosphorus. In the most productive years silica use was more intense. The abyssal part of the wind-shielded Weggis-Vitznau basin is the most sensitive spot to the effects of nutrients in the lake. This paper is a summary of a more extensive report of the data (Biihrer and Ambilhl 1996).