Assessing Ecological Quality of A Stream Using Trait-Based Phytoplankton Approach

The aim of this inquiry was to evaluate the efficacy of the Q(r) index, designed for river environments and applied for the first time to Turkish rivers, in delineating the water quality of the Çorum Stream. We were also intrigued by deducing the primary pollutants via trait-oriented phytoplankton community analysis and evaluating the functional categories that impact the final estimations of the Q(r) index. Monthly collection of environmental parameters and phytoplankton samples were conducted at six locations (St1‒St6). Despite seasonal variations, “good” water quality was generally found in upstream (St1, St2), where slow-flowing and mesotrophic conditions prevailed. In midstream (St3, St4), “-poor” water quality was observed during the spring–autumn, while “moderate” water quality was recorded in dowmnstream (St5, St6) throughout the year. While St3 and St4 exhibited elevated organic matter levels and eutrophic conditions, St5 and St6 demonstrated increased flow rates and mixed water characteristics. Principal Component Analysis (PCA) highlighted that DO, Temp, TP and o-PO4 emerged as the primary environmental factors affecting phytoplankton communities in the Çorum Stream (p < 0.05). In the phytoplankton community, Bacillariophyta became the dominant division, constituting 44.3% of the total abundance and comprising 46 taxa. Lepocinclis ovum, Euglenaformis proxima, and Ulnaria ulna were determined as the most dominant species among phytoplanktonic taxa of the Çorum Stream. Some FGs (W1, MP, TC) being linked to high Q(r) values, their dominance influenced water quality estimation performed by the Q(r). We conclude that the Q(r) index proved effective in evaluating the lotic water ecosystems.