Stable isotopes and chemical characteristics of precipitation in Hangzhou and Huzhou, East China
2019
Jin, Zanfang | Wang, Yan | Li, Feili | Qian, Lijing | Hu, Yuming | Shi, Yasheng
Atmospheric precipitation is a very important link in the water cycle. The characteristics of major ions (n = 341) and stable isotopes (δ²H, δ¹⁸O; n = 157) were analysed in Hangzhou and Huzhou, which are economically prosperous cities in East China. The δ²H and δ¹⁸O values of precipitation ranged from − 109.70 to 21.30‰ and from − 14.87 to − 0.95‰, respectively. Compared with the local meteoric water line (LMWL) of China, the slope and intercept of the LMWL were much higher in Hangzhou and Huzhou, which is related to the effects of the humid climate and less secondary evaporation. The δ²H and δ¹⁸O values were highest in spring because of the influence of air masses from the northern Asian continent and other nearby sources. In contrast, the air masses from the South China Sea and the western Pacific Ocean in the summer had the lowest δ²H and δ¹⁸O. The dominant ions in precipitation indicate that Ca²⁺, HCO₃⁻, SO₄²⁻, NH₄⁺ and NO₃⁻ are the main ions of precipitation in Hangzhou and Huzhou, and the dilution of precipitation leads to lower concentrations of ions in spring and summer, similar to the values found in most Chinese cities. The increase in motor vehicle use resulted in a lower [SO₄²⁻]/[NO₃⁻] ratio (1.64) of precipitation, indicating mixed acid rain in Hangzhou and Huzhou (HZS). Based on a combination of the correlation analysis, enrichment factors and source contributions, we determined that SO₄²⁻ and NO₃⁻ were introduced mainly from anthropogenic activities such as coal combustion and vehicle exhaust, accounting for 89% and 99%, respectively. The strong correlation between Cl⁻ and Na⁺, as well as Ca²⁺, Mg²⁺ and K⁺, indicates that these ions commonly have marine and crustal origins, respectively, and 40% of Mg²⁺ comes from a marine source.
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