Quality: Management, Sanitation and Investigation
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.
© | Dipl.-Biol.
Hartmut Willmitzer | 31.07. 2000 | Copyright