Ecological status estimation of minimally disturbed rivers of the Western Mediterranean Basin (Turkiye) using diatom indices

The Water Framework Directive (WFD) suggests establishing reference conditions to help evaluate the ecological status of rivers in a specific ecoregion. Here we used eighteen diatom indices to estimate the ecological status of 44 candidate rivers for reference conditions in Turkiye's Western Mediterranean Basin. We collected data on epilithic diatoms and environmental variables three times (spring, summer, and fall) in 2017. Based on the redundancy analysis (RDA), seven environmental parameters significantly affected the distribution of abundant and indicator diatom species. Indicator species highly correlated with nitrate-nitrogen (NO3-N) and total nitrogen (TN). These two environmental parameters also showed significant correlations with the Pampean Diatom Index (IDP), the Eutrophication/Pollution Index (EPI-D), the Trophic Diatom Index (TDI), and the Rott's Saprobic Index (ROTTs). Therefore, here we focused on the ecological quality status indication by these four indices. The TDI index was more consistent for estimating our streams' ecological status and revealed high ecological status for fifteen sampling sites. We conclude that areas with high ecological status will help set up a reference condition for future studies in the Western Mediterranean Basin and other basins in Turkiye.