First record of fossil algal diversity in Lake Sevan, Armenia: Illuminating ecological dynamics and environmental parameters

Algae serve as valuable proxies for paleoenvironmental reconstructions in sedimentary environments. Fossil algae from Middle to Late Holocene sediments, alongside pollen data, enrich our understanding of environmental changes, particularly evident in the Tsovinar-1 section of Lake Sevan, Armenia.

Botryococcus and Pediastrum/Pseudopediastrum are sensitive indicators of hydrological changes and reflect fluctuations in lake level. The comparatively high abundance of Pediastrum/Pseudopediastrum and Botryococcus from 6000 BC to 4400 ca. BC, when water levels were elevated, together with the occurrence of the genera Gomphonema, Fragilaria, Cymbella, and Epithemia during high lake level phases, underscores their utility as pelagic indicators. From 4400 to 2600 ca. BC, no aquatic vegetation is recorded at Tsovinar-1 under relatively more arid conditions. Later, from 2600 to 1400 ca. BC the lake level rose again and eutrophic conditions in some shallow areas along the coastal zone developed, indicated by high abundances of the nitrogen-fixing cyanobacterium Gloeotrichia. Later, after 600 ca. BC, further variations in water level occurred and are mirrored in algal abundances. Changes of pH followed those trends of water level and are mainly reflected in the occurrences of Zygnematophyceae, particularly with high numbers of Spirogyra and Mougeotia.

The results suggest that algal species hold a valuable potential for paleoecological reconstructions, calling for further studies across diverse environmental gradients. Notably, the first documentation of Gloeotrichia in the fossil record of the Caucasus provides a new proxy for the analysis of environmental changes in lakes and pools of the Armenian Highland.