Combination of two indication systems in pre-alpine lakes — diatom index and macrophyte index

Since the climax of eutrophication in the early 1980s mainly greater lakes have been investigated and monitored in terms of their nutrient charge. In the future there will still be a need to develop guidelines for monitoring the trophic status of smaller lakes. Four small lakes were investigated by the author in the years 1996 and 1997. In order to define the nutrient charge of those lakes more precisely, special emphasis has been put upon the two criteria diatoms and macrophytes. Eventually an evaluation of the lakesʹ catchment areas will also be an important component of these studies. Benthic diatoms are the main part of periphyton. As unicellular fast reproducing organisms they are excellent indicators for trophic situations in lakes. The diatom index denotes the trophic status of the littoral zone during the last few weeks before sampling. The macrophytes, however, reflect the nutrient charge over a longer period, i.e. several years. The macrophyte index is based on the fact that some species are most prevalent at certain nutrient loads. The effort to combine these two indication systems carries a high resolution of spatial nutrient changes as well as in temporally changes.