Wirkungsbezogene Immissionsgrenzwerte für Phosphor in Fließgewässern - Fallstudie Rott

Flow regulations of rivers result in elevated retention times and in subsequent eutrophication effects, such as algal mass development. These phenomena were studied in a small river and its shallow flood retention basin (River Rott, Lower Bavaria) from 1982 to 1988. Algal mass developments (median value at the outlet: 125, 90 percentile > 300 myg/l Chlorophyll = Chl) significantly exceed those in the Rivers Ruhr and Main in both in concentration and duration. The latter rivers are similar in nutrient contents. The main reasons for this deviation in the River Rott system are thought to be the shallowness of the flood retention basin and the high content of riverine solids in the water. We assume that the latter fact favours diatom dominance throughout the whole year. The Phosphorus limits which control eutrophication effects for the Rivers Ruhr and Main are far too high for the River Rott and will not reduce algal mass development in this system.