Ionic composition variation characteristics and regression analysis of spring water in Jinan City

Taking SO₄ ²⁻, NO₃ ⁻, Cl⁻ in spring water in Jinan City as the research objects, the influence factors from three aspects of precipitation, source supplement and human activities were selected, and the correlation between the influence factors and the concentrations of the three ions was studied. The path analysis was used to determine the direct and indirect effects of the influencing factors. The action size and direction of the influencing factors on the change of ion concentrations were determined by calculating the decision coefficient. The regression equation was established and used to predict the concentration of NO₃ ⁻ in spring water and the total amount of wastewater that could be carried by environment. The results showed that the concentration of SO₄ ²⁻, Cl⁻ and NO₃ ⁻ in spring water showed an upward trend, and SO₄ ²⁻ and Cl⁻ increased significantly (P < 0.01) from 2008 to 2019. There was a significant positive correlation between the amount of wastewater and the concentration of SO ₄ ²⁻ and Cl⁻ (P < 0.01, P < 0.05), and the correlation coefficients were 0.811 and 0.577, respectively. There was a significant positive correlation between the concentration of H ⁺ and NO₃ ⁻ in source supplement reservoir (P < 0.05), and the correlation coefficient was 0.692. Among the influencing factors, the amount of wastewater had the greatest direct effect on the concentration of SO ₄ ²⁻, Cl⁻ and NO₃ ⁻ in spring water. The amount of wastewater played an increasing role in the change of SO₄ ²⁻ and Cl⁻ concentrations. Precipitation, H⁺ concentration and the amount of wastewater in reservoir played an increasing role in NO₃ ⁻ concentration change of spring water , and H⁺ in reservoir was the main decision variable. The equation predicted that NO₃ ⁻ concentration of spring water would be 8.42 mg/L in 2020, meeting Class Ⅲ standard of Quality Standard for Ground Water (GB/T 14818-2017). If NO₃ ⁻ concentration of spring water kept below 10 mg/L, the total amount of wastewater could be controlled within 6324 million cubic meters.