Ion composition and its controlling factors of surface water in Shangluo region

Shangluo region is an an important water sources area of Middle Route Project of South-to-North Water Diversion. However, the main ion composition and its sources of surface water in the region are still not clear. Based on the analysis of surface water samples, we find that the main cation concentration is in the order of Ca2+>Mg2+>Na+>K+, the main anion concentration is in the order of HCO-3>SO2-4>Cl->NO2-3, the hydrochemical type is HCO3-Ca, overall, the surface water quality is good. In addition, rock weathering is the main controlling mechanism of surface water ions sources in the region. The rock weathering mainly happens in carbonate rocks such as limestone and marble, and halite weathering also exists. Evaporation and crystallization have strong effect on ion composition，but the influence of atmospheric precipitation is relatively weak. The human activities in Shangluo region don't obviously change the surface water ion composition.