Elimination of Nutrients in the Rozkoš-Reservoir

The reservoir, having a volume of 76 hm³, a surface area of 1001 ha and a maximum depth of 17 m, is divided by a dam into two parts. Half of the upper part with an area of 200 ha is densely covered by macrophytes (Elodea, Potamogeton). The three main tributaries with 2.6 m³/s on an average are highly polluted and show α-mesosaprobic conditions. The reservoir is investigated between September and March in its longitudinal section at eight stations. The organic load and the total solids show a total decrease by 60% and 66%, respectively, and 70% of this selfpurification occurs in the upper, separated part of the reservoir. In the same way, also the total nitrogen is reduced, whereas the total phosphorus is reduced already in the upper part of the reservoir by 71%, then decreasing to 21% in the second part of the reservoir. With phosphorus, besides the biological elimination obviously also precipitation by the dissolved iron occurs, the concentration of which is reduced by 44 or 76%, resp. The bacteriological load of water improved by two to three orders of magnitude.