Mesohalobic diatom species in the freshwater Lake Itkul (Khakassia, Russia)

Abstract

This study presents a list of mesohalobic diatom species found in the freshwater Lake Itkul between 2006 and 2025. The lake is located in the steppe zone of the Republic of Khakassia, within the Bele-Shirinsky endorheic region. We identified 28 species and intraspecific taxa of mesohalobic diatoms belonging to 17 genera. Mesohalobes are typically scarce and play no significant role in the algocenosis; however, their diversity and development intensity in the periphyton are slightly greater than in other communities. The occurrence frequency is provided for each taxon. The most active species in the periphyton in terms of relative occurrence frequency are: Navicula capitatoradiata H. Germain ex Gasse (up to 90%), Mastogloia danseyi (Thwaites) Thwaites ex W. Smith (up to 53.3%), M. elliptica (C. Agardh) Cleve (up to 44.2%), and Nitzschia denticula Grunow (up to 69.8%). In 2024–2025, there was a significant increase in the local populations of Navicula capitatoradiata and Mastogloia elliptica in the epilithon and epiphyton communities. A decrease in lake water levels, caused by the annual rise in air and water temperatures alongside localized salinization of the littoral zones, likely impacts the percentage ratio of salinity indicator groups and the proliferation of mesohalobic species.