Case study 2 (Bulgaria): Diatom sampling in the Rila Mountains, Bulgaria, 09-10 July 2015

Didymosphenia geminata (Didymo) is a freshwater diatom which has historically been found in cool, oligotrophic waters of northern Europe and northern North America. Since the mid-1980s it has increasingly been observed in new area, e.g. New Zealand, Iceland and high elevation Alpine areas. Although Didymo does not present a significant human health risk it can form massive blooms and have negative impacts on stream habitats, hampering fishery and degrading the recreational value of streams.

In the framework of the ESENIAS-TOOLS project (Case study 2: Comparative study on the effect of hydrological regime on the distribution of the invasive diatom Didymosphenia geminata in extreme environments), a first field trip to the Bulgarian study site, the Rila Mountains (the highest massif on the Balkan Peninsula, Southwestern Bulgaria), was organised on 9 and 10 July 2015. These activities were jointly coordinated by the project leaders Asst. Prof. Dr. David Finger from the Reykjavik University, Iceland, and Prof. Dr. Nadja Ognjanova, from the Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences (IBER-BAS), Sofia, Bulgaria.

Scientists from IBER-BAS and a PhD student Ruben Josif from the Ovidius University of Constanta, Romania, participated in the first field trip. During the field trip all seven high-mountain lakes were sampled in the Sedemte Ezera Cirque, Rila Mountains. Epilithic diatom samples were collected at 14 sites according to standard methods.

Furthermore, historic data were assimilated: In Bulgaria, single frustules of Didymosphenia geminata were recorded in two epilithic diatom samples from Bliznaka Lake, Sedemte Ezera Cirque, Rila Mountains, during a study in 2000-2001.

 This case study aims at:

- Standardisation of methods regarding sampling/ identification/ monitoring of Didymo/ diatoms.

- Collecting available data on the occurrence and abundance of Didymo and other diatoms in the high-mountain lakes and tributaries (Rila Mountains) based on literature and field data;

- Collecting environmental data and studying the relation to biological data;

- Identifying differences in diatom qualitative and quantitative composition between sites where the diatom is found and it is not, and comparing with the previous study period.