Isotopic characteristics, chemical composition and salinization of atmospheric precipitation in Shahrood, northeastern Iran

摘要

Knowledge of chemical and isotopic composition of precipitation is an important tool for climatological, meteorological and hydrological applications. Rain and snow samples collected during June 2009 to November 2013 in Shahrood, northeastern Iran, have been analyzed for stable isotopes and physico-chemical constituents. Local Meteoric Water Line is characterized by a slope of 5.47 and the isotopic composition of precipitation is generally controlled by air temperature and the amount of precipitation. The precipitation electrical conductivity (EC), ranging from 10 to 1,970 μS/cm (mean: 201 μS/cm, SD: ±275), largely depends on the amount of precipitation and the number of dry days preceding each event. Snow samples have lower ECs. Volumes weighted mean (VWM) pH of the samples is 7.35 (mean: 7.53, SD: ±0.37) with only few acidic samples. Sulfate and calcium are the major ions in the precipitation, a consequence of widespread exposure of carbonates and urban and agricultural inputs. High nitrate concentration (VWM: 3.36 mg/L) reflects the impact of extensive fertilizer application in the region. Compared to years 2000-2001, the VWM EC of the precipitation has risen by 51 % from 41.7 to 63.1 μS/cm; 38 % of the rise is due to reduction in precipitation and 13 % is attributed to increased atmospheric pollution. Chemically, the main rise is in SO_4~(-2), followed by Na~+ and NO_3~-. Dramatic rise in the number of vehicles in the country from 4 million to 17 million and 77 % increase in petroleum products consumption, are considered as the causes of salinization of atmospheric precipitation.