Stagnant lentic waters

Furthermore, within these main types various more detailed classifications have been elaborated, taking into consideration different criteria. In general, physical, chemical and biological parameters are combined, such as content of oxygen, content of nutrients, colour and water transparency, and the richness and diversity of biological habitat. 

Ponds are artificial, rather shallow and sometimes emptied (astatic) water reservoirs. Generally, they are more rich in nutrients and are more biologically alive than the lakes, and they are liable to faster changes. Often intensive care is paid to them and thus their natural development is artificially changed. 

In stagnant waters some common characteristics determine the life conditions in a dam. They concern primarily light and thermal conditions, content of oxygen, and the distribution of suspended and soluble substances. 

Light conditions. For the light conditions, three main zones can occur in stagnant waters (Fig. 4.4)  

Littoral zone a zone of shallow water where practically all the light penetrates to the bottom. In natural reservoirs this zone is usually overgrown with root-bearing plants, in controlled ponds it need not be overgrown. 

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