This study is the first comprehensive hydrochemical investigation of 25 rivers in Khorasan Razavi, the second most populated province in Iran. Surface water provides the dominant part of agricultural water in this province. The results of this study demonstrated that rock weathering is the dominant factor controlling water quality in river samples. Stable isotopes (δ18O and δ2H) also demonstrated that river samples were mainly plotted below Mashahd Meteoric Water Line (MMWL), with negligible deviation due to low evaporation effect. However, dam reservoir samples showed notable deviation from MMWL due to huge surface evaporation. River water in all stations is considered appropriate for agricultural proposes based on Wilcox diagram and residual carbonate index, and also for potable usages (except for a few stations) according to World Health Organization protocols. The results of this study can be used by the scientists in Iran Ministry of Agriculture for the future agricultural management programs.

Keywords