Ecological Status of Shallow Lakes in the Bulgarian Danube River Floodplain According to the ECOFRAME Approach: Testing a System for Integrated Ecological Quality Assessment

In this study four shallow lakes, situated in the Bulgarian Danube River floodplains were tested for the assessment of their ecological status. According to the Bulgarian legislation, the ecological classification of lakes and reservoirs is based mainly on physical parameters and on two biological quality elements, and namely phytoplankton and macrophytes. The other three widely used biological quality elements, macrozoobenthos, fish and zooplankton communities, are not adopted yet. An integrated method designed for the ecological assessment of shallow lakes called ECOFRAME approach was tested. This system had been developed for the implementation of the Water Framework Directive and included the application of other biotic variables. Our investigation was conducted in the summer of 2012. Most of the samples were collected and processed as described in the ECOFRAME methodology, or by the state-of-the-art methods. According to the analysed biotic variables, only the Srebarna Lake was assessed as a lake with Moderate ecological quality, while the other three sites were assessed as with Poor ecological quality. The ecological assessment based on abiotc variables determined Poor ecological quality for all of the studied lakes and it was accepted as being the final assessment of the ecological status. The results obtained suggest that the ECOFRAME method for ecological assessment needs further verification for the specific conditions in the shallow oxbow lakes on the Lower Danube River floodplain.