Limnological Effects of the Elimination of Phosphorus from the Wahnbach Reservoir

Abstract

The elimination of the phosphorus compounds from the River Wahnbach (100 - 150 µg/l Ptot) at the point where it flows into the Wahnbach Reservoir down to a figure of 5 µg/l Ptot has decreased the total phosphorus concentration in the Wahnbach Reservoir to 8 - 10 µg/l Ptot. As a result of this, the impoundment which had been in an eutrophic state became oligotrophic to mesotrophic within 3 years. The blue-green algae which had been predominant disappeared and diatoms grow again every spring. Algal growth has been reduced to such an extent that the transparency has gone up to a Secchi-depth of 10 m and was 6 m on an annual average. This was solely produced by eliminating phosphorus and without eliminating nitrogen at the same time (the annual average N-concentration of all tributaries was 5 mg/l).