Spatial and temporal variation of salt ions in the surface water of Shule River Valley in Gansu Province, China

The objective of the study was to assess the quality of the Shule River water for irrigational purposes. Surface water samples were collected along the course of the river in May and October 2012. The samples were analyzed for pH, electrical conductivity (EC), bicarbonate, chloride, sulphate, sodium, potassium, calcium and magnesium. Surface water was generally alkaline (average pH 8.17) and water pH and total dissolved solids in May were higher than those in October. EC ranged from 0.24 to 2.15 mS cm−1. Sodium was identified as the dominant cation, sulphate was identified as the dominant anion in May for both samples of river water but, in October, the dominant anions are respectively sulphate, bicarbonate and chloride from the upper region to the lower region. The total dissolved solids, chloride and sodium were found to exceed the permissible limits for irrigation water in the lower region. According to the principal factor analysis results, among water quality parameters measured in this study, chloride is the best indicator for monitoring water quality. The results revealed a deteriorating water quality in the lower region of the river.