Development of water quality index as a sustainability indicator in Küçükçekmece watershed, İstanbul

Abstract

Küçükçekmece Watershed, located in the European side of Istanbul is a highly deteriorated and polluted region as a result of unplanned urbanization and industrialization. The purpose of this study is to assess the water quality trends in Küçükçekmece Lagoon and in its tributaries Eskinoz and Sazlıdere Creeks by using an aggregate water quality index (WQI). The index aimed to focus on issues such as organic contamination, euthrophication and stresses on aquatic species with a set of parameters including dissolved oxygen, chemical oxygen demand, chlorophyll-a, total nitrogen to total phosphorus ratio, nitrate, orthophosphate, turbidity, electrical conductivity and pH. These parameters were normalized and subsequently aggregated by a weighted sum function. The final scores were represented on a scale between 0 and 100. The water quality data evaluated by the index covered the total of 14 stations and a period of more than 5 years. The results have showed that the index approach can be effective to indicate problems such as seasons of algal blooms or long-term pollution trends. According to the results, the most polluted stations of the Watershed were found as E2 and E3 at Eskinoz Creek while station D3, located on Sazlıdere Dam, was found as the least polluted. During the algal blooming seasons, sharp declines were observed in the index scores and the water quality dropped below “critical” levels. Consistently, low COD and dissolved oxygen scores were found at many stations, which can be accepted as an evidence of high industrial and domestic discharges into the Basin.