Chemical characteristics and source analysis on ionic composition of rainwater collected in the Carpathians “Cold Pole,” Ciuc basin, Eastern Carpathians, Romania

Abstract

A study of precipitation chemistry was conducted for 11 years (01 January 2006–31 December 2016) in the Ciuc basin, Eastern Carpathians, Romania. The studied area is an enclosed basin, also called "the Carpathians cold pole." All collected samples were analyzed for major cations and anions. HCO₃⁻ concentrations were calculated based on the empirical relationship between pH and HCO₃⁻. The multiannual arithmetic mean of pH values was found to be 6.57. The lowest and highest pH values were measured in 2009 and 2013, being 6.57% lower, respectively, 7.57% higher than the multiannual mean. Only 3.31% of the studied rainwater samples indicate acidic character. In descending order, the majority of the samples are as follows: NH₄⁺ >Ca²⁺ >SO₄²⁻ >Cl⁻ >HCO₃⁻ >NO₃⁻ >Na⁺ >K⁺ >Mg²⁺ >NO₂⁻ >H⁺. Principal component analysis (PCA) showed the NH₄⁺, Ca²⁺, and Mg²⁺ contribution to the neutralization process and their sources. The anthropogenic origin of SO₄²⁻ was supported by the high non-sea-salt fraction (NSSF) (~ 91%). The results of this study suggest that rainwater chemistry is strongly influenced by local natural and anthropogenic sources (agricultural activities) rather than marine sources. The pollutants in rainwater samples were mainly derived from calcareous and dolomitic soil dust and specific local climatic conditions, long-range transport, local industry, and traffic sources.