Assessment of running water quality in the Asi River Basin (Türkiye) using diatom indices

Ecological quality evaluations using diatoms, which are accepted as one of the biological quality components have accelerated recently in different basins of Türkiye. Asi Basin which has a small catchment area within the borders of Türkiye, located near to Syrian border and is under the influence of a Mediterranean climate. This study aims to determine the water quality of the streams in this basin by using various diatom indices and to determine the environmental pressures affecting the diatom community structure. In this study, 21 rivers of the Asi Basin were sampled three times during 2019 to evaluate their ecological status by using 18 different diatom indices. A total of 157 diatom taxa were recorded in these rivers. Different environmental variables were also sampled combined with diatoms, and according to RDA, alkalinity (ALK), electrical conductivity (EC), total phosphorus (TP), and total nitrogen (TN) were determined as the most decisive pressures for the distribution of diatom assemblages. In terms of TN, Bayrak River (R7), while in terms of TP, Üçocak River (R12) have II. class water quality. The eight diatom indices showed significant correlations with TP (p < 0.01). The Trophic-Saprobic index (LOBO) showed the highest response to the TP (R² = 0.63) and was consistent with the indicator species. This index was also compatible with the evaluation results made according to the water quality classes of the sites. LOBO index classified these rivers as high-good or poor-bad effectively in terms of TP. It was the first time that the LOBO which was developed to evaluate the surface freshwaters of Brazil has a high correlation with TP in a basin of Türkiye.