Temporal and spatial dynamics of nitrogen and phosphorus in surface water and sediments of a transboundary river located in the semi-arid region of Turkey

Abstract

Abstract The Tigris River with a catchment area of about 57,614 km2, is an important water source for the Southeastern Anatolia Region of Turkey. With the development of industry and agriculture, and the growth of urban population in the region, its pollution has become a serious problem. Pollution from domestic, industrial and agricultural activities has led to deterioration of water quality. Total nitrogen (TN) and total phosphorus (TP) levels in water and sediments of the Tigris River were analyzed at seven different sites spread over the river stretch of about 500 km during the period of February 2008 to January 2009. Cluster analysis, analysis of variance (ANOVA) and correlation analysis were performed to explore temporal and spatial variations of TN and TP in the river. The results revealed that TN and TP concentrations of water and sediments in the wet season were higher than those in the dry season. Based on the median TN:TP ratios in water column, P was limiting nutrient at sites 2 and 5, while N was limiting nutrient at sites 4 and 7. The median TN:TP ratio in water column was 11.8 times higher than that in the sediment. According to trophic state classification, the river was classified as eutrophic based on both mean and median concentrations of TN and TP. Cluster analysis indicated that TN and TP concentrations in water column were higher in the urban areas. TP concentrations in sediment were found higher at sites receiving agricultural runoff and mine wastewater discharge, while TN concentrations were found higher at sites receiving untreated domestic wastewater. TN and TP concentrations in sediments at all sites were below the SEL (severe effect levels), suggesting that harmful effects on sediment-dwelling organisms are not expected.