Diatom diversity and community structure of the littoral zone of Lake Ugii, Mongolia

Abstract

Lake Ugii, one of the largest freshwater lakes in central Mongolia, has experienced increasing anthropogenic pressure and environmental change over recent decades. To evaluate the current ecological condition of the lake shoreline, diatom assemblages were investigated at multiple sampling sites around the lake and associated habitats. A total of 86 diatom taxa were identified in 2024, compared with 110 taxa reported in 2009, indicating a decline in species richness over the past fifteen years. Elevated phosphorus concentration indicators were recorded along the northern and northeastern shoreline, suggesting the influence of organic inputs from surrounding riparian areas. Additionally, there was low substrate stability at sites along the Hooloy River, Hoid Mergen Shanaa, and Saidiin Hoshuu. Multivariate analyses revealed significant spatial variation in diatom community composition among sampling sites (PERMANOVA; R²=0.554; p=0.001), while differences in within-site dispersion were not significant (PERMDISP; p=0.087). Indicator Species Analysis identified five significant indicator taxa, including Diatoma vulgaris Bory, Nitzschia palea (Kützing) W.Smith, Encyonema elginense (Krammer) D.G.Mann, Epithemia sorex Kützing, and Diatoma tenuis C.Agardh. Although measured physicochemical variables (conductivity, temperature, total dissolved solids, salinity, and pH) did not show significant relationships with community composition, spatial differences among assemblages suggest the influence of local shoreline conditions and ongoing land-use changes within the watershed. Comparison with previous surveys indicates a significant decline in diatom diversity and a marked shift in shoreline community composition in Lake Ugii. These findings provide important baseline information for ecosystem monitoring, conservation planning, and sustainable management of the lake and its watershed.