Decadal patterns of anthropogenic salinisation in typical mountain streams in northeastern China: Increased rates and...

Salt pollution and anthropogenic-accelerated weathering is globally shifting the ionic composition and increasing salinisation of fresh water. We analyzed a 40-year data set (1970s-2010s) to characterize the drastic change of dissolved ionic composition, conductivity and pH levels. We also identified causative factors in these highly polluted mountain streams in northeastern China. Dissolved salt ions (Ca²⁺, Mg²⁺ and SO₄^2-) increased by 3.02-5.21 fold and conductivity (a proxy for salinisation) increased by 3.09 fold. The average pH values increased from 7.08 to 8.49. The dominant ions, Ca²⁺, Mg²⁺, SO₄^2- and HCO₃^- + CO₃^2-, accounted for ∼90% of ionic composition based on mass concentration. Between the 1970s and 2010s, the dominant anion shifted from HCO₃^- + CO₃^2- to a mixture of SO₄^2- and HCO₃^- + CO₃^2-. Increasing mining and land development appear to be the primary driving factors for the change of Ca²⁺, Mg²⁺, SO₄^2- and HCO₃^- + CO₃^2- concentrations; whereas, agricultural land was the main driving factor for the variation in K⁺, Na⁺ and Cl^- concentrations. The source of ions has shifted from a more natural weathering of carbonate rocks to one of mineral dissolution that is affected by anthropogenic activities. Our study shows that freshwater mountain streams are at risk of long lasting anthropogenic salinisation and should be considered in future management and conservation plans.