Hydrochemical characteristics of surface water in main rivers of the irrigation districts in the downstream of Yellow River

This paper investigated spatial variations in chemical characteristics, hydrochemistry type and sources of major ions in water. It analyzed the composition of chemical ions in surface water of Majia River, Dehuixin River and Yinhuangguanqu of the irrigation districts in the downstream of Yellow River. The study attempted to lay the theoretical guidelines for long-term observation of hydrochemical changes of surface water and groundwater under irrigation from the Yellow River. In addition, the paper provided the scientific basis for evaluating water environment conditions and pollution prevention measures. The results showed that pH and elec-trical conductivity (EC) varied in space. Surface water in the study area was alkaline with pH range of 7.65~9.34. EC of the water samples was in the range of 965~1 530 μs·cm^-1. The ranges of concentration of NO₃^- , SO₄^2- , HCO₃^- , Cl^-, Ca²⁺, Mg²⁺, Na⁺, K⁺ were respectively 1.32~60.15 mg·L^-1, 53.41~781.90 mg·L ^-1, 143.35~823.50 mg·L^-1, 98.00~564.00 mg·L^-1, 22.57~265.00 mg·L ^-1, 29.41~195.50 mg·L^-1, 103.20~472.00 mg·L^-1 and 0.83~59.05 mg·L ^-1. The major ions and their average concentrations were as follows: HCO₃^- (330.45 mg·L ^-1) > SO₄^2- (308.48 mg·L ^-1) > Cl^- (286.83 mg·L^-1) > NO₃^- (29.60 mg·L^-1) and Na⁺ (236.85 mg·L^-1) > Ca²⁺ (98.15 mg·L^-1) > Mg²⁺ (82.62 mg·L^-1) > K⁺ (9.05 mg·L^-1). The hydrochemical type of the surface water was Na⁺·Ca²⁺-HCO₃^-·SO₄^2- . The pH and Cl^- of Majia River along with mean Mg²⁺ concentration were highest in the three rivers. Mean EC, concentrations of NO₃^- and HCO₃^- were highest in Dehuixin River. Also mean concentrations of SO₄^2- , Na⁺, Ca²⁺ and K⁺ for Yinhuangguanqu were higher than those for the other two rivers. The Piper diagrams suggested that the hydrochemical types of the surface waters were different for different rivers. Water assessment showed that water in study area was suitable for irrigation. Correlation analysis showed that Ca²⁺, Mg²⁺ and Na⁺ were significantly correlated with SO₄² and Cl^-. Furthermore, Ca²⁺ and Mg²⁺, Na⁺ and K⁺, and SO₄^2- and Cl^- were significantly correlated. The results suggested inter-related influence or same source water ions in the region which were likely driven by human activity.