The effects of various lake typologies on the distribution of Chironomus spp. (Diptera), and arguments on optional factors of Water Framework Directive in Turkiye

: Countries with heterogeneous climatic and geographic characteristics may find it challenging and limiting to fulfill the requirements of the Water Framework Directive (WFD), such as defining ecoregion and water body types. To overcome this limitation, they implement optional factors in addition to the obligatory factors defined in the WFD. As a candidate country, Türkiye is required to comply with the WFD requirements and must determine its own optional and obligatory factors. In this context, we addressed the relevance of Chironomus spp. in determining these factors. We used twenty distinct national lake typologies for Türkiye and identified a total of 24 Chironomus species. The Chironomus genus was found to be effective in determining the optional factors. Statistical analyses revealed that fetch, altitude, salinity, water temperature, pH, saturated and dissolved oxygen, conductivity, orthophosphate, ferrous ion, chloride, and nitrogen compounds were significant in discriminating the regions. The canonical correspondence analysis (CCA) explained 56.62% of the variance. We also statistically analyzed the effectiveness of the class boundaries of the obligatory factors used in Türkiye for regionalization. Among the official obligatory factors, only the altitude boundaries gave a significant result and explained a total of 62% variance. We recommend revising the class boundaries of obligatory factors and using fetch data as a significant genuine parameter for lake typology as an optional factor