This work focuses on an integrated approach for lake ecological status assessment, elaborated according to the requirements of the European Water Framework Directive (WFD). Data from five lowland and semi-mountain lakes in Bulgaria (Southeast Europe) collected from two years (2011-2012) form the basis for an integrated assessment and the definition of reference conditions. Several metrics were applied in combination, to classify lakes into five ecological status classes. Assemblages of aquatic organisms: phytoplankton, macrophytes and benthic macroinvertebrates, together with 11 supporting physico-chemical parameters were studied. The assessed unique conditions suggested that reference conditions of Bulgarian lakes have natural variability. This first baseline study illustrated specific cases within the lake types that should be assessed in details before providing standardized classification systems in compliance with the requirements of WFD.

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The trophic structure of benthic macroinvertebrates in three different types of running water bodies subjected to varying degrees of anthropogenic pressure was analyzed. A seasonal survey was conducted at three Bulgarian rivers in 2011. An adapted version of the multihabitat sampling method was applied along with measuring physical and chemical variables. The ecological status was defined by means of biotic and trophic indexes. Distribution of the functional feeding groups shows that the most sensitive groups, shredders and scrapers, dominate the trophic structure of the mountain river types. In contrast, groups of deposit feeders and filterers prevail at the foothill and plain rivers. Multidimensional scaling plot and redundancy analysis demonstrated that anthropogenic impact and altitude are the main factors determining the distribution of the benthic macroinvertebrates by different functional groups. Seasonality has no leading role in the trophic structure formation of the benthic communities. Our results showed a difference between the trophic composition of the macrozoobenthos found in the mountain sections and those found in the foothill/plain stretches of the rivers. A comparison between the last two areas demonstrated that there was no clear distinction between the trophic composition of the functional feeding groups.