Ecological assessment of lentic ecosystems in Ceyhan River Basin using phytoplankton indices

Increasing exploitation of water resources has led to declining water quality in aquatic environments. Freshwater ecosystems face various environmental pressures, such as the impacts of climate change and intensifying land-use practices. This study aimed to assess the ecological preferences of phytoplankton communities and determine the ecological status (ES) of several reservoirs and lakes in Ceyhan River Basin across different seasons. A canonical correspondence analysis was conducted to understand the associations between phytoplankton assemblages and stressors in freshwater ecosystems, revealing a strong correlation of 97%. The factors that most influenced the distribution of phytoplankton species were electrical conductivity (EC), temperature, total phosphorus, biological oxygen demand (BOD5), and altitude. High values of EC, BOD5, and nutrients were recorded in Hakkıbeyli Reservoir. Among the studied ecosystems, only Hakkıbeyli Reservoir exhibited a TN:TP ratio greater than 29:1, which corresponded to the highest cyanobacterial biovolume observed. The bioassessment study indicated that the MPTI-modified phytoplankton trophic index fit well to the logTP gradient, whereas Phyto-Tr did not. The MPTI revealed that the lakes and reservoirs had a moderate ES. The MPTI may provide more accurate assessments of the ES of lakes and reservoirs in Ceyhan River Basin. The results highlight the importance of understanding how different phytoplankton species respond to environmental factors across diverse ecosystems. Such insights are crucial for assessing the ecological condition of standing water ecosystems and provide essential information for their management and conservation.