Situation of twenty-five Swedish lakes now and 40 years ago

Summary

Twenty-five Swedish lakes which were studied for the first time in the beginning of 1930's have been reinvestigated in order to analyse the human influence. This investigation included different types of lakes. Some lakes have received heavy nutrient loads. The conductivity of the lakes varied in the previous investigation between 20 and 600 μS/cm and now between 30 and 1000 μS/cm. Sulphate concentrations have increased strongly. In all lakes there is now at least twice the concentration as stated in the 1930's. Photographs of the aquatic vegetation taken in the 1930's and 1975 show changes in distribution.