Water Biological Sufficiency and Quality of the Bulgarian Danube Stretch (845–375 River Km)

The possibility of categorizing water biological sufficiency and quality through criteria for state biotic standards has been evaluated for 7 sections of the Bulgarian Danube stretch. The results of saprobiological analysis show the relatively stable beta-mesosaprobic level of the entire studied stretch, while indices of the structural organization of the benthic invertebrate communities do not correspond to this and rather correspond to the status of zoobenthos in different types of bottom substrata distributed over the length and width of the stretch. We discuss the necessity of further studies for the precise definition of criteria and norms for the assessment of the water biological sufficiency and quality, corresponding to the specific Danube conditions.