Diatoms (Bacillariophyta) living on the surface of snow in the Northern Urals, Russia

Samples were taken from the surface of red-brown colored snow to a depth of 4 cm using sterile plastic tubes. Diatoms were identified by their morphological characteristics in permanent preparations mounted in Elyashev’s medium. The material was examined at 1000x magnification under a Biolam-I (Russia) light microscope after treating the samples with concentrated sulfuric acid to clean the frustules.

For diatom identification, standard taxonomic guides (Krammer & Lange-Bertalot, 1986, 1988, 1991a, 1991b; Krammer, 2000, 2003, and others) and several monographic works were used. Current algal nomenclature follows the international database "AlgaeBase" (Guiry & Guiry, 2026). A total of 29 Bacillariophyta species were found.

The diatom assemblage of the snowfield comprises algae from two ecological groups. The first group consists of typical freshwater algae. The second group includes aerophilic organisms, often found in soils, on mosses, and in caves.

Among the species identified, Pinnularia borealis, P. obscura, Nitzschia alpina, and Luticola suecorum can be considered aerophilic. The taxon Diatoma mesodon occurred with the highest abundance. The composition of the diatom assemblage in the snowfield corresponds to conditions found in oligotrophic or oligodystrophic habitats.

The low concentration of basic ions and organic substances in the snowmelt water favored the development of halophobous and predominantly acidophilic diatoms, such as Diatoma mesodon, Fragilariforma virescens, Eunotia exigua, Pinnularia borealis, P. sinistra, Psammothidium helveticum, Tabellaria flocculosa, and others. Their species composition is similar to that found in the periphyton and benthos of streams, rivers, and springs in mountainous and foothill areas of various geographical regions.

According to literature data, some of these species (Diatoma mesodon, Eunotia exigua, Pinnularia borealis, Tabellaria flocculosa) have also been recorded in the cryoseston of perennial snowfields in mountain systems, in glacial crevices, and in ice cores. From the identified diversity, only Pinnularia borealis can be classified as a typical cryophile. The development of algocoenoses and their distribution in the snowfield may be primarily associated with the proximity of the stream, from which algal cells are transported on the snow cover by numerous birds.

Additionally, temporary meltwater pools forming in the spring may also serve as sources for snow patch inhabitants. Another possible pathway for the introduction of algae, other microorganisms, and nutrients is the transport of eolian fine earth from the surface of surrounding landscapes, as has been observed in other mountain regions. This organic dust has been found to contain cyanobacteria, green algae, diatoms, moss and fungal spores, and plant pollen (Harper, 1999; Papina et al., 2013).