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.
Highlights
The Global Network of Isotopes in Precipitation (GNIP) was initiated in 1958 by the International Atomic Energy Agency (IAEA) and the World Meteorological Organisation (WMO), and became operational in 1961
The objective was to make a systematic collection of data on the isotopic composition, i.e. stable isotopes of hydrogen and oxygen and radioactive hydrogen isotope, of precipitation across the globe to determine temporal and spatial variations of isotope ratios in precipitation
GNIP was focused on monitoring atmospheric thermonuclear test fallout through levels of radioactive tritium and, after 1970, became an observation network of stable hydrogen and oxygen isotope data for hydrologic investigations of water resources
Summary
The Global Network of Isotopes in Precipitation (GNIP) was initiated in 1958 by the International Atomic Energy Agency (IAEA) and the World Meteorological Organisation (WMO), and became operational in 1961. GNIP was focused on monitoring atmospheric thermonuclear test fallout through levels of radioactive tritium and, after 1970, became an observation network of stable hydrogen and oxygen isotope data for hydrologic investigations of water resources. The isotopic composition of precipitation in Ljubljana (Slovenia) has been performed by the Jožef Stefan Institute (JSI) since 1981. To begin with, monitoring was performed in cooperation with the Hydrometeorological Survey of Slovenia ( the Slovenian Environmental Agency, SEA), the Ru|er Bo{kovi} Institute (RBI; Zagreb, Croatia) and the IAEA. Details of the history of isotope monitoring since the beginning in 1981 until 2006, together with data evaluation, have been reported in Vre^a et al (2008)
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