Local factors or altitudinal gradient: which one is effective on diatom communities and ecological status in the 23 lentic systems of the Sakarya Basin (Türkiye)?

In the 23 lentic systems of the Sakarya Basin, littoral diatoms and environmental variables were assessed with the samples collected in the spring, summer, and fall of 2018 to determine the effect of altitude or local factors on diatom assemblages. A total of 210 diatom taxa in 63 genera were identified during the studied period. Both the distribution of indicator species and the species composition were affected by pH, electrical conductivity, alkalinity, total organic carbon, total nitrogen, and total phosphorus. Especially low alkalinity was found to be effective in the distribution of high-altitude optima species. Close geographical location was also important in shaping species composition. Although the species richness and diversity of lentic systems on > 1600 m a.s.l. were higher than those in lower altitudes, pH and total phosphorus were the determinant factors. On the other hand, altitude indirectly affected all these factors by causing habitat diversity. The Leclercq and Maquet Diatomic Index showed a higher correlation with total nitrogen, total organic carbon, and total phosphorus. This index was more effective in determining the ecological status of 23 lentic systems. Altitude has also an indirect effect on the ecological status of these systems by restricting anthropogenic pressure such as total phosphorus.