[Hydrochemical Characteristics and Possible Controls of the Surface Water in Ranwu Lake Basin]

Abstract

To study the chemistry of surface water and potential control measures in the Ranwu Lake basin, 19 samples were collected from Ranwu Lake in 2019. Conventional hydrochemical techniques and statistical analysis methods (descriptive statistics, the Gibbs figure, ion ratio, Piper triangular diagrams) were applied to better understand the solute geochemistry and surface water hydrochemistry in the Ranwu Lake catchment. Surface water in the Ranwu catchment is slightly alkaline (pH of the samples ranged from 7.54 to 8.48 with an average value of 8.06). The concentrations of total dissolved solids (TDS) in the water range from 59.89 to 96.75 mg ·L^-1 with an average of 79.98 mg ·L^-1, the total dissolved solids of all samples are less than 100 mg ·L^-1 and belong to fresh water. The TDS are dominated by Ca²⁺, Mg²⁺, HCO₃^-, and SO₄^2- in the Ranwu Lake. The ion concentrations in the lake water samples are in the order of Ca²⁺ > Mg²⁺ > Na⁺ > K⁺. The concentrations of Na⁺and K⁺are very low. Ranging from 0.5 to 1.21 mg ·L^-1, with an average value of 0.58 mg ·L^-1, the equivalent concentration of Ca²⁺ accounts for 63.3% to 76.2% of total cations with an average value of 67.2%. The equivalent concentration of Mg²⁺ accounts for 23.4% to 36.2% of total cations with an average value of 31.4%. Ca²⁺ and Mg²⁺ account for 98.5% of total cations. The main anions were HCO₃^- and SO₄^2-. The equivalent concentration of HCO₃^- accounts for 74.31% to 84.29% of total anions with an average value of 78.21%. The equivalent concentration of SO₄^2- accounts for 9.59% to 19.37% of total anions with an average value of 15.34%. HCO₃^- and SO₄^2- together account for 93.55% of total anions on average. All the water samples fall in the water-rock interaction field, which suggests that the weathering of rocks primarily controls the major ion chemistry of groundwater in this area. Solutes are mainly derived from carbonate weathering and silicate weathering. The role of cation exchange in the geochemical process of the lake and the influence of human activities on the lake are found to be weak.

Keywords: Ranwu Lake; chemical weathering; element rations; hydrochemistry; ion source.