VARIATIONS OF THE STRUCTURE OF BIOLOGICAL COMMUNITIES RELATED TO SALINITY IN SOME SALINE LAKES FROM ROMANIA.

The study was conducted in several natural saline lakes from the Buzău and Brăila counties (Romania). The Lakes Câineni, Balta Albă and Amara are hyposaline, only the Lake Movila Miresei can be considered as hypersaline according to mineral content. The aim of the study was to have an quantitative approach to the biological structure of the lakes in relationship with abiotic factors, mainly salinity. Using the Principal Component Analysis (PCA), the Lake Movila Miresei was associated with salinity and conductivity, the Lake Câineni with temperature, while Balta Albă and Amara were influenced mainly by DO, pH, TDS, ORP, turbidity. The level of primary producers was represented by four groups of phytoplankton and the highest species richness was registered in Lake Amara (38 species), with low salinity. The zooplankton community showed a species richness significantly smaller than phytoplankton, even if it presented species belonging to several taxonomic groups (9). The high zooplankton diversity of the Lake Amara was correlated with low salinity. The Shannon index decreasead with the reduction of salinity in the other three lakes. It is noteworthy the presence of Artemia salina Linnaeus 1758, both in the Lakes Amara and Movila Miresei, known as indicator species of therapeutic mud. The additional technique applied for investigating the diversity of the phytoplankton confirmed the values of Shannon's diversity index and infirmed the values of the species richness trend. Thus, the Lake Câineni (with high salinity, second after Movila Miresei) held the first place in terms of diversity, the second was Balta Albă, and the less diverse were Amara and Movila Miresei. The Amara Lake experienced an cyanobacterial bloom event, with Oscillatoria tenuis Agardh 1813. We conclude that salinity not always is the main factor shaping the diversity of saline lakes. Other factors, such as temperature, DO, pH, TDS, ORP, turbidity can influence the biological communities of these lakes. [ABSTRACT FROM AUTHOR]