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Water Quality: Management, Sanitation and Investigation

Limnological Fundamentals

Natural Settings

Extensive restoration measures are only useful if the basic load coming from natural causes as determined by volume of water (Graphic example) and size of intake area is exceed (Graphic example). No meso or oligotrophic conditions can be achieved for example, in spite of low external load. Even slight pollution in inflows leads to growth of algae in the lit-up water strata of the reservoir. Small reservoirs with a small volume of water only have a small hypolimnetic volume so that the oxygen necessary for decomposition is insufficient: this can lead in turn to retroactive nutrient solutions coming from the sediment. The nutrients with short duration in the reservoir lead additionally to increased occurrence of phytoplanktons, since comprehensive decomposition of the plankton within the food web becomes more difficult.


This applies to the Neustadt and Erletor reservoirs, in Thuringia with a water volume of approx. 0.5 million m3 and a catchment area of approx. 5,5 km2 which can only have a mesotropic character in spite of low pollution in the inflows (total-P < 0,01 mg/l). Large reservoirs with the same pollution in the inflows and with relatively small catchment areas (Ohra reservoir 17 Mil m3 capacity, catchment area 34 km2) reach oligotrophic conditions with visible depths of up to 20 m.

Graphic example


© | Dipl.-Biol. Hartmut Willmitzer |  31.07. 2000 | Copyright