Temporal Variation of Total Nitrogen and Total Phosphorus in Surface Waters from the Lower Çoruh River Basin, Turkey

Abstract

The aim of this study is to monitor and assess the surface water quality in the Lower Çoruh River Basin, northeast Turkey.Several key water-quality indicators were measured: total nitrogen, total phosphate phosphorus, chemical oxygen demand, and chlorophyll a (Chl a).In situ monitoring and the surface water sampling studies in the Çoruh River, the Murgul Stream, and the Borçka Dam Lake were conducted monthly during a period of one year.On an annual basis, the Çoruh River had a little bit higher total nitrogen concentration ranging from 0.335 mg/l to 1.300 mg/l, but a little bit lower chemical oxygen demand concentration varying between 2.66 mg/l and 9.12 mg/l, compared to Murgul Stream.Total phosphate phosphorus concentration was almost the same throughout the lower basin and was about 0.090 mg/l.Chl a concentration, which was 1.422 µg/l in Çoruh and 1.062 µg/l in Murgul, had shown an increasing trend and reached 3.193 µg/l in the Borçka Dam Lake.The measured results reveal that the Çoruh River and the Murgul Stream have high-quality water, considering total nitrogen and chemical oxygen demand, but slightly polluted water regarding total phosphate phosphorus, with reference to the Turkish Surface Water Quality Regulation.The Borçka Dam Lake was classified as oligotrophic in terms of Chl a, mesotrophic in terms of total nitrogen, and eutrophic in terms of total phosphate phosphorus.Considering the decrease in the annual average values of total nitrogen and chemical oxygen demand, it is concluded that the Borçka Dam Lake had a positive effect on the surface water quality in the Lower Çoruh River Basin.