Phosphorus elimination ensures clarity

This ongoing research project investigates the process of the concentration of phosphates in lakes and rivers. The aim is to derive recommendations for action for the water management.

In Berlin, the Tegeler See and Schlachtensee were successfully rehabilitated by a drastic reduction in the external phosphorus burden. The visibility increased from a few centimetres to several metres in summer. Today these lakes are the cleanest parts of the Berlin lakes and rivers system. The aim of the ongoing study project in the Kompetenzzentrum Wasser Berlin gGmbH is to develop a better understanding of the process through a systematic evaluation of the data gathered during the rehabilitation in order to be able to derive recommendations for action for the water management.

The investigations to date show that even after the rehabilitation, 30 to 40 percent of the water entering the Tegeler See comes from the Havel, but that this source now supplies 80 percent of the phosphorus freight. This freight is sufficient to keep the phosphorus concentration in the Tegeler See significantly higher than in the Schlachtensee, and therefore to “charge” the sediments with phosphorus. For some years the sediments in the Tegeler See proved to be phosphorus traps, for other years they were sources of phosphorus. Overall the importance of the redissolving of phosphorus is very much greater in the Tegeler See than in the Schlachtensee where the generally very good water quality is impaired slightly by the external transport of phosphorus into the lake from the immediate catchment area in winter.