Chemical and isotopic interpretation of major ion compositions from precipitation: a one-year temporal monitoring study in Wrocław, SW Poland

Abstract

The chemical compositions (Na+, NH4 +, K+, Mg2+, Ca2+, Cl−, NO2 −, NO3 −, SO4 2−, HCO3 −) of wet precipitation and nitrogen isotope compositions δ15N(NH4 +) were studied from January to December 2010 in Wrocław (SW Poland). Results of a principle component analysis show that 82 % of the data variability can be explained by three main factors: 1) F1 (40 %) observed during vegetative season (electrical conductivity, HCO3 −, NO3 −, NO2 −, NH4 + and SO4 2−), mainly controlling rainwater mineralization; 2) F2 (26 %) observed during vegetative and heating seasons (K+, Ca2+ and Mg2+), probably representing a combination of two processes: anthropogenic dusts and fertilizers application in agricultural fields, and 3) F3 (16 %) reported mainly during heating season (Na+ and Cl−) probably indicating the influence of marine aerosols. Variations of δ15N(NH4 +) from −11.5 to 18.5 ‰ identify three main pathways for the formation of NH4 +: 1) equilibrium fractionation between NH3 and NH4 +; 2) kinetic exchange between NH3 and NH4 +; 3) NH4 + exchange between atmospheric salts particles and precipitation. The coupled chemical/statistical analysis and δ15N(NH4 +) approach shows that while fossil fuels burning is the main source of NH4 + in precipitation during the heating season, during the vegetative season NH4 + originates from local sewage irrigation fields in Osobowice or agricultural fertilizers.