Water quality assessment of Aksu stream and Acısu creek using water quality indices

Aksu Stream, one of the rivers in the Antalya River Basin, feeding Kovada I and Kovada II Hydroelectric Power Plants and Karacaoren Dam, is under hydrological pressure as a result of the operating regime of Karacaoren Dam Lake, irrigation water abstractions, and precipitation irregularities due to global climate change. Acısu Creek, the second application area of the thesis study, where intensive greenhouse activities are carried out, is an important surface water resource and a valuable region for tourism. Therefore, sustainable management of water quality and quantity is necessary and important in the mentioned areas. Within the scope of the project numbered 119Y267 supported by TÜBİTAK, water quality monitoring studies were carried out monthly for 1 year, during the period of September 2020 and September 2021, at 24 monitoring stations in total for both Aksu Stream and Acısu Creek. For the interpretation of the monitoring data sets, the Canadian Council of Ministers of the Environment Water Quality Index (CCME-WQI), National Sanitation Foundation Water Quality Index (NSF-WQI), Aquatic Toxicity Index (ATI), and Water Quality Assessment System (SEQ-Eau) were applied comparatively and the most appropriate index method was determined in classifying water quality of the study areas. Correlation analysis results were taken into account in determining the most appropriate index method. Accordingly, the highest correlation (0.94) was obtained between SEQ-Eau and CCME water quality indices, while the lowest correlation (0.56) was found between SEQ-Eau and NSF indices. Similar results were obtained in Acısu Creek, the second study area. Accordingly, the highest correlation (0.95) was achieved between SEQ-Eau and CCME water quality indices, while the lowest correlation (0.60) was found between SEQ-Eau and NSF indices. It has been revealed that CCME and SEQ-Eau indices give compatible and very close results, thereby they are the most appropriate indices for both study areas. In addition, the water quality classes were determined by using the monthly measurement and analysis results of the physicochemical parameters (color measurements at three different wavelengths, pH, EC, COD, BOD5, NH4-N, NO3-N, TN, PO4-P, TP, F-) according to the Surface Water Quality Regulation (SWQR). According to this regulation, ten monitoring stations were classified as good and two stations were classified as fair quality for Aksu Stream. In case of Acısu Creek, six monitoring stations were classified to have good water quality and six monitoring stations with fair quality. The common parameters that impair water quality are TP, BOD5, DO, and EC. Moreover, during the monitoring studies, dry and stagnant water conditions were observed at some of the monitoring stations due to changing climatic conditions, reduced precipitation and runoff.