Strontium concentrations and isotope ratios in a forest-river system in the South Qinling Mts., China

• Dissolved Sr and 87Sr/86Sr ratios show significant differences among water types.
• Dissolved Sr is positively related with most ions and physicochemical parameters.
• Atmospheric inputs, carbonate and silicate weathering are the three end-members.
• The three end-members control the river water chemistry.
• The three end-members averagely contribute 74%, 20%, and 6% to the river water.

The concentrations of dissolved strontium (Sr) and isotope ratios (87Sr/86Sr) in rainwater, river water, and water from forest soil are measured to investigate the contributions of these sources to a river during base flow conditions in the relatively pristine South Qinling Mountains, China. Dissolved Sr concentrations and 87Sr/86Sr ratios vary significantly between different water types (p < 0.01) suggesting that it is suitable for differentiating sources. Dissolved Sr is also positively correlated with most ions and a range of physicochemical parameters (p < 0.01 and p < 0.05 respectively) in water samples including Ca2+, Mg2+, EC, and TDS (p < 0.001) indicating their similarities in the drivers of biogeochemical processes and common origins. The correlations between Sr isotopes and Ca/Na, Ca/K, and 1000/Sr ratios suggest that three end-members of atmospheric inputs, carbonate and silicate weathering control the Sr water chemistry in the river water. Using the three-source mixing model, atmospheric inputs, carbonate, and silicate weathering contribute 74%, 20%, and 6% respectively to the dissolved Sr in the river water. This research has provided new insights into the contribution of sources of Sr to a river system in a mountainous catchment.

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