Quantifying long-term changes in water quality and quantity of Euphrates and Tigris rivers, Turkey.

The Euphrates and Tigris watersheds originating from Turkey and passing through Syria and Iraq are one of the most important transboundary watersheds in the Middle East. Long-term data (1971 to 2002) from 14 stations over the Euphrates river and seven stations over the Tigris river were analyzed and compared using the nonparametric Kruskal-Wallis and Mann-Kendall trend tests, and box-and-whisker plots. The upper Euphrates river had significantly lower values of flow rate (FR), water temperature (WT), electrical conductivity (EC), Cl, and SO4 than did the lower Euphrates river. The middle Euphrates river had significantly higher Na, K, HCO3, Cl, sodium adsorption ratio (SAR), and boron (B) and lower EC and SO4 than the lower Euphrates river. The upper west Tigris river had higher EC, Ca+Mg, and SO4 and lower FR, Na, and SAR than the lower Tigris river. The upper east Tigris river had higher HCO3 and B and lower FR and WT than the lower Tigris river.