Isotopic composition of precipitation at the Station Ljubljana (Reaktor), Slovenia - period 2007-2010

Abstract

The stable isotopic composition of hydrogen and oxygen (δ2H and δ18O) and the tritium activity (A) were monitored in monthly collected precipitation at Ljubljana (Reaktor) during the period 2007-2010. Monthly and yearly isotope variations are discussed and compared with those observed over the period 1981-2006 and with the basic meteorological Parameters for Ljubljana (Bežigrad) and Ljubljana (Hrastje) stations for the period 2007-2010. The mean values for δ2H and δ18O, weighted by precipitation amount at Ljubljana (Reaktor), are -59.4 ‰ and -8.71 ‰. The reduced major axis local meteoric water line (LMWLRMA) is δ2H = (8.19 ± 0.22)×δ18O + (11.52 ± 1.97), while the precipitation weighted least Square regression results in LMWLPWLSR-Re δ2H = (7.94 ± 0.21)×δ18O + (9.76 ± 1.93). The lack of significant difference in the LMWL slopes indicates a relatively homogeneous distribution of monthly precipitation as well as the small number of low-amount monthly precipitation events with low deuterium excess. The deuterium excess weighted mean value is 10.3 ‰ which indicates the prevailing influence of the Atlantic air masses. The temperature coefficient of δ18O is 0.30 ‰/°C. Tritium activity in monthly precipitation shows typical seasonal variations, with a weighted mean tritium activity in this period of 8.5 TU. No decrease of mean annual activity is observed.