Assessment of ecological status and preliminary results on reference conditions in alpine glacial lakes (Bulgaria) - a contribution to the implementation of the water framework directive

Abstract

The 'normative definitions' of ecological water quality classes given by the Water Framework Directive (WFD) are narrative descriptions of the conditions present in water bodies of different qualities relative to reference conditions found in unimpacted sites. Defining the type-specific reference conditions for water bodies and finding biological metrics that sensitively reflect only the anthropogenic deviations from those conditions are the biggest challenges that the ecological status assessment faces. This study aimed at phytoplankton, macrophyte, macro-invertebrates and fish-based assessment in two high mountain glacial lakes and establishing preliminary reference conditions. The lakes are located in Rila and Pirin Mountains, Southwest Bulgaria. Chernoto Lake is ultra-oligotrophic and has abundant submerged macrophytes; Bezbog Lake is also oligotrophic with submerged macrophytes, both with macrozoobenthic communities typical for oligosaprobic conditions. Sampling was carried out from July to September in 2009 and 2011. The biological and water quality parameters in the lakes are discussed. Indices elaborated in a European context (Algae Group Index, Reference Index, adapted biotic index, Pantle & Buck's saprobic index and German trophic index PETI) were tested on the collected data set. The type-specific taxa for the studied lake type were preliminarily determined.