GEOLOGIJA 59/1, 67-84, Ljubljana 2016 http://dx.doi.org/10.5474/geologija.2016.004 © Author(s) 2016. CC Atribution 4.0 License Slovenian Network of Isotopes in Precipitation (SLONIP) -a review of activities in the period 1981-2015 Slovenska mreža opazovanj izotopske sestave padavin (SLONIP) - pregled aktivnosti v obdobju 1981-2015 Polona VREČA1 & Neža MALENŠEK2 1Department of Environmental Sciences, Jožef Stefan Institute, Jamova cesta 39, SI-1000 Ljubljana, Slovenia; e-mail: polona.vreca@ijs.si 2Department of Geology, Faculty of Natural Sciences and Engineering, University of Ljubljana, Aškerčeva cesta 12, SI-1000 Ljubljana, Slovenia Prejeto / Received 5. 5. 2016; Sprejeto / Accepted 9. 6. 2016; Objavljeno na spletu / Published online 11. 8. 2016 Key words: precipitation, isotopes, oxygen, hydrogen, tritium, GNIP, SLONIP, Slovenia Ključne besede: padavine, izotopi, kisik, vodik, tritij, GNIP, SLONIP, Slovenija Abstract The first investigations of oxygen and hydrogen isotope composition (¿18O and ¿>2H) and the tritium activity (3H) in precipitation over Slovenia were performed in the frame of tracer experiments conducted in the period 1972-1975 in the Ljubljanica River drainage basin. The first regular and systematic monitoring of isotope composition of precipitation only began in 1981 in Ljubljana but has been extended during the last 35 years to 30 different locations countrywide. Herein, we present a review of research performed during the period 1981-2015. We collected information about sampling, analytical methods, available data and their evaluation including calculations of local meteoric water lines. Based on the data, we identify gaps in the research and make recommendations for future monitoring in the frame of the Slovenian Network of Isotopes in Precipitation (SLONIP). Izvleček Prve raziskave izotopske sestave kisika in vodika (¿18O in ¿>2H) ter aktivnosti tritija (3H) v padavinah na območju Slovenije so potekale v okviru sledilnih poskusov, ki so se v obdobju 1972-1975 izvajali na območju reke Ljubljanice. Prvo redno in sistematično spremljanje izotopske sestave padavin se je pričelo leta 1981 v Ljubljani in bilo zadnjih 35 let izvajano na 30 različnih lokacijah. V prispevku podajamo pregled raziskav, ki so bile v Sloveniji opravljene v obdobju 1981-2015. Zbrali smo podatke o vzorčenju, uporabljenih analiznih postopkih, dostopnih rezultatih in obdelavah podatkov vključno z izračuni lokalnih meteornih premic. Na osnovi zbranih informacij smo identificirali pomanjkljivosti predhodnih raziskav in izdelali priporočila za bodoče raziskave v okviru Slovenske mreže opazovanj izotopske sestave padavin (SLONIP). Introduction The importance of systematically collecting data on the water isotope composition of precipitation, i.e. stable isotopes of oxygen (expressed as ¿18O) and hydrogen (expressed as c>2H) and the radioactive hydrogen isotope tritium (3H), in the frame of the Global Network of Isotopes in Precipitation (GNIP) has been steadily increasing since it was initiated by the International Atomic Energy Agency (IAEA) and the World Meteorological Organisation (WMO) in 1958 (Internet 1). Initially, the 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 GNIP provides also an important database for verifying and improving atmospheric circulation models, studying regional, global and temporal climates, studying the interactions between water in the atmosphere and the biosphere, providing baseline information for the authentication of commodities, tracking 68 Polona VREČA & Neža MALENŠEK migratory species and for forensic purposes. Particularly in the last decade has the demand for accurate spatial and temporal predictions of point, regional, and continental-scale ¿18O and c>2H values in precipitation been increasing (Terzer et al., 2013). This is especially the case for those regions where little or no GNIP data exist. In Slovenia water isotopes in precipitation have been systematically monitored since 1981 only in Ljubljana (Pezdič, 1999). In 2000, the need for a much more refined understanding of isotope variations was identified due to geographical diversity, which influences the climate and also the water cycle in Slovenia considerably. Therefore, a programme of collecting new data at a higher spatial density and temporal frequency in different parts of the country has been initiated and was extended several times during the last 15 years. Consequently, the number of sampling locations has grown to a Slovenian Network of Isotopes in Precipitation (SLONIP). Unfortunately, the network is still not a part of a national monitoring programme, such as that operating in European countries, for example, in Switzerland (Schurch et al., 2003) and Germany (Stumpp et al., 2014). In the past 35 years, water isotopes in precipitation were monitored in Slovenia by different institutions mostly in the frame of short-term research projects and many isotope data were collected but only partly evaluated and published. The data were used in many hydrological and hydrogeological investigations, as well as in investigations of precipitation, moisture recycling in Alpine regions, identification and characterisation of nitrate pollution sources, in evaluations of GNIP data, investigations of bottled waters (e.g. Brenčič et al., 2015; Mezga, 2014; Vreča et al., 2014, 2015a and references therein) and other studies related to food authentication (Bizjak Bat et al., 2012). A growing need for water isotope data and the establishment of the SLONIP database, which could be used in other applications, particularly in water resources research and food authentication, stimulated the authors to review the activities performed in Slovenia in the period 1981-2015. The main aims of this paper are the following: 1) to review the history of isotope in precipitation investigations performed in Slovenia in the period 1981-2015, 2) to summarize the main information about sampling, analytical methods used and basic isotope data for a particular sampling location, 3) to identify the main gaps in the research, and 4) to present general recommendations for future work in the frame of SLONIP. Materials and methods We collected available publications: national and international journals, conference papers, PhD theses, and Master theses, reporting data on isotope composition of oxygen and hydrogen in precipitation over Slovenia during the period 1981-2015. We also searched the following databases: Google, Google Scholar, Co-operative Online Bibliographic System and Service -COBISS along with unpublished material including internal reports available at the Jožef Stefan Institute (JSI). The following information were collected: 1. sampling data including location -coordinates, type of sampling station, sampling period, sampling collector, sample treatment including filtration and type of storage bottle. 2. analytical methods used for determining stable oxygen (¿18O) and hydrogen (c>2H) isotope composition. 3. analytical methods used for determining tritium activity (3H) if available together with stable isotope data. 4. reported isotope data, mean isotope values and local meteoric water lines (LMWLs). Publications in which isotope composition of precipitation was mentioned but it was not clear where, when or how sampling was performed, which analytical methods were used and reporting limited or no numerical data, were used to prepare a list of the main gaps and general guidelines for future work in the frame of SLONIP. Results and discussion History of isotopes in precipitation investigations performed in Slovenia in the period 1981-2015 Water isotopes were applied in Slovenia for the first time in investigations in the frame of extensive underground water tracing performed in the period 1972-1975 in the Ljubljanica River drainage basin by the international Association of Tracer Hydrology (Gospodarič & Habič, 1976). Samples of precipitation were collected at the Šmarata, Postojna and Logatec meteorological stations. Stable isotopes of oxygen and hydrogen were determined in Munich, Germany and tritium activity in Vienna, Austria. Later, in the early 1980s, isotope ratio mass spectrometer (IRMS) techniques for determining stable oxygen and hydrogen isotope composition in water samples were implemented for the first time also in Slovenia at the JSI. The first systematic monitoring of isotopes in precipitation started in 1981 at the Slovenian Network of Isotopes in Precipitation (SLONIP) - a review of activities in the period 1981-2015. 69 synoptic station Ljubljana-Bežigrad located at the Hydrometeorological Survey of Slovenia (today Slovenian Environment Agency - ARSO; Fig. 1, Tab. 1, Pezdič, 1999; Vreča et al. 2008). In 1993, the collection of precipitation was moved to the JSI (station Ljubljana-IJS) and finally, in September 2000 to the Reactor Centre of the JSI (station Ljubljana-Reaktor) in the vicinity of Ljubljana (Fig. 1, Tab. 1, Vreča et al., 2008). The stable isotope composition of monthly precipitation samples was determined at the JSI and tritium activity was measured at the Ruder Boškovic Institute (RBI) in Zagreb, Croatia (Krajcar Bronič et al., 1998; Pezdič, 1999; Vreča et al., 2008). Data have been regularly reported to the IAEA and published until 1994 in the IAEA Technical Reports Series (IAEA 1986, 1990, 1994), and afterwards on the internet (Internet 2). Later, in 2008, a review of all data collected in the period 1981-2006 was performed and sampling history recorded (Vreča et al., 2008). New data and corrections were submitted to the IAEA G NIP database (Internet 2). Data collected in the period 2007-2010 were reported and evaluated by Vreča et al. (2014) and the whole 1981-2010 dataset was used for the first time to study the relation between isotope composition of precipitation and atmospheric circulation patterns (Brenčič et al., 2015). Monitoring of water isotopes in precipitation was carried out continuously and systematically by the JSI until 2000 only in Ljubljana (Tab. 1, Vreča et al., 2008). A short-term monthly stable isotope monitoring was performed in 1999 and 2000 also at the ARSO precipitation station in Sela na Krasu (Fig. 1, Tab. 1, Doctor, 2002) and at Sinji vrh (Tab. 1, Trček, 2003). Due to the geographical diversity, which influences the climate of Slovenia considerably (Pučnik, 1980) and the large karstic aquifers important for the water supply of SW Slovenia, sampling was extended to two stations, namely to the ARSO synoptic station Portorož airport and the ARSO precipitation station Kozina in October 2000 (Fig. 1, Tab. 1). At both stations stable and radioactive water isotopes were monitored on a monthly basis (Vreča et al., 20052007, 2009, 2011, 2015a). Unfortunately, since 2004, due to the lack of financial support monitoring has been continued only at the Portorož airport. First monitoring of stable water isotopes in precipitation in eastern Slovenia started in 2001 in Selniška Dobrava (Fig. 1, Tab. 1, Mali, 2006), and was performed by the staff of the Geological Survey of Slovenia (GeoZS). Afterwards, in 2009 two additional locations were selected by the JSI for monitoring stable oxygen and hydrogen isotope composition in SW and SE Slovenia, one at the Fig. 1. Slovenian Network of Isotopes in Precipitation (SLONIP) according to sampling station type. 70 Polona VREČA & Neža MALENŠEK Table 1. Sampling locations and types of sampling station within SLONIP (1 - synoptic station ARSO; 2 - climatological station ARSO; 3 - precipitation station ARSO; 4 - precipitation station at JSI; 5 - others), GNIP code, coordinates and altitude of the sampling station, as well as period of sampling (n.r. - not reported). Location1 (x ... type of station) GNIP code Coordinates Altitude (m a.s.l.) Sampling period N E 1a Ljubljana-Bežigrad1 1401500 46°03'56'' 14°30'45'' 299 1981-1992 1b Ljubljana-IJS4 1401500 46°02'31'' 14°29'16'' 292 1993-08/2000 1c Ljubljana-Reaktoi4 1401500 46°05'41'' 14°35'50'' 282 09/2000- 2 Portorož airport1 1410501 45°28'31'' 13°36'58'' 2 10/2000- 3 Kozina3 1411001 45°36'15'' 13°55'54'' 486 10/2000-12/2003 4 Dvor3 1411801 45°48'12'' 14°57'41'' 195 2009-2012 5 Postojna2 1411200 45°45'58'' 14°11'34'' 533 2009- 6 Kredarica1 1400800 46°22'45'' 13°50'57'' 2514 03/2010- 7 Rateče1 1400700 46°29'50'' 13°42'47'' 864 03/2010- 8 Bohinjska Češnjica2 1400601 46°17'39'' 13°56'32'' 595 03/2010-06/2014 9 Zgornja Radovna3 1400801 46°25'42'' 13°56'36'' 750 04/2010- 10 Podljubelj3 1401001 46°23'48'' 14°17'17'' 740 03/2010-06/2014 11 Velenje5 - 46°21'36'' 15°07'43'' 433 09/2012-05/2015 12 Murska Sobota1 - 46°39'08'' 16°11'29'' 189 2015- 13 Kleče5 - n.r. n.r. n.r. 1997-1998 14 Blatnik5 - n.r. n.r. n.r. 1998-1999 15 Ponikve5 - n.r. n.r. n.r. 1998-1999 16 Sinji vrh5 - n.r. n.r. n.r. 1999-2000 17 Sela na Krasu3 - 45°49'15'' 13°37'38'' 270 08/1999-10/2000 18 Selniška Dobrava5 - 46°32' 15°28' 295 1/2001-10/2005 19 Union brewery, Ljubljana5 - n.r. n.r. n.r. 07/2003-06/2005 20 Postojna cave5 - n.r. n.r. n.r. 2004-2005 21 Rogaška Slatina5 - n.r. n.r. n.r. 2008-2010 22 Postojna Karst Research Institute5 - n.r. n.r. n.r. 03/2010-02/2011 23 Ilirska Bistrica5 - n.r. n.r. 1043 03/2011-02/2012 24 Snežnik5 - n.r. n.r. 1300 03/2011-03/2012 ARSO climatological station Postojna (Fig. 1, Tab. 1, Lojen, personal communication) and the second at the ARSO precipitation station Dvor (Fig. 1, Tab. 1, Zavadlav, 2013). Because none of the sampling locations was situated in the mountainous, northwestern part of Slovenia that represents an important water resource, we established in 2010 additional isotope monitoring of precipitation at five ARSO meteorological stations in the Julian Alps and Karavanke including the following: Kredarica, Rateče, Bohinjska Češnjica, Zgornja Radovna and Podljubelj (Fig.1, Tab. 1, Vreča et al., 2013). At all five locations stable and radioactive water isotopes (Vreča et al., 2013, 2015b; Vreča, 2015) were monitored until July 2014. Since then, monitoring has been continued at Kredarica, Rateče and Zgornja Radovna. In autumn 2012 monitoring of oxygen and hydrogen isotope Slovenian Network of Isotopes in Precipitation (SLONIP) - a review of activities in the period 1981-2015. 71 composition in Velenje was established (Fig. 1, Tab. 1, Kanduč et al., 2014) and in 2015 also in northeastern Slovenia at the ARSO synoptic station Murska Sobota (Lojen, personal communication). Oxygen and hydrogen in precipitation were monitored monthly also at the Union brewery in Ljubljana during the period 2003-2005 by Trček (2005, 2006), at the Postojna cave in the period 2004-2005 by Kogovšek & Urbanc (2007), at Rogaška Slatina during the period 2008-2010 by Trček & Leis (2011) and at Ilirska Bistrica and Snežnik during 2011-2012 (Mance et al., 2014). In addition, the staff of the GeoZS performed monitoring at Klariči, Korentan, Ptuj and at their institute in Ljubljana (Urbanc, personal communication). Only the isotope composition of oxygen was monitored at Ljubljana (Kleče) in the period 1997-1998 by Urbanc & Jamnik (1998), at Blatnik and Ponikve in the period 1998-1999 by Location Sampling collector Sample bottles and analytical methods References ¿■"O 3H 1a Ljubljana-Bežigrad b PE IRMS CO2 equil. PE IRMS Zn red. to H2 PE GPC Pezdič,1999, 2003 Vreča et al., 2008 1b Ljubljana-IJS a PE IRMS CO2 equil. PE IRMS Zn red. to H2 IRMS Cr red. to H2 PE GPC 1c Ljubljana-Reaktor a filt. 589/1 PE, b-gl. IRMS CO2 equil. filt. 589/1 PE, b-gl. IRMS Cr red. to H2 HDPE GPC,LSC-EE Vreča et al., 2014 2 Portorož airport (until 2002) d PE IRMS CO2 equil. PE IRMS Cr red. to H2 n.d. GPC Vreča et al., 20052007, 2009, 2011, 2015a Portorož airport (since 2002) b filt. 589/1 b-gl. IRMS CO2 equil. filt. 589/1 b-gl. IRMS Cr red. to H2 HDPE GPC,LSC-EE 3 Kozina b filt. 589/1 PE, b-gl. IRMS (CO2 equil.) filt. 589/1 PE, b-ql. IRMS Cr red. to H2 HDPE GPC,LSC-EE Vreča et al., 20052007, 2009 4 Dvor b filt. 589/3 HDPE IRMS CO2 equil. filt. 589/3 HDPE LAS n.d. Zavadlav, 2013 JSI unpublished data 5 Postojna b HDPE IRMS CO2 equil. HDPE, b-gl. LAS HDPE, b-gl. LAS n.d. Zavadlav et al., 2012 MANDiČ, 2013 JSI unpublished data 6 Kredarica b filt. 589/1 b-gl. IRMS CO2 equil. filt. 589/1 HDPE, b-gl. LAS filt. 589/1 HDPE, b-gl. LAS filt. 589/1 HDPE LSC-EE Vreča et al., 2012, 2015 JSI unpublished data 7 Rateče b 8 Bohinjska Češnjica b 9 Zgornja Radovna b 10 Podljubelj b 11 Velenje other IRMS CO2 equil. IRMS H2 equil. n.d. Kanduč et al., 2014 12 Murska Sobota b b-gl. Analysis in progress b-gl. Analysis in progress n.d. Lojen, personal communication 13 Kleče n.r. IRMS CO2 equil. n.d. n.d. Urbanc & Jamnik, 1998 14 Blatnik n.r. IRMS CO2 equil. n.d. n.d. Lapanje, 2000 15 Ponikve n.r. IRMS CO2 equil. n.d. n.d. Lapanje, 2000 Table 2. Sampling and analytical methods. HDPE - high-density polyethylene bottles with sealing caps, 50 and 500 mL; PE -polyethylene bottles with sealing caps; b-gl. - borosilicate glass bottles with double caps, 30 or 50 mL; b-pl. - plastic bottle; IRMS - isotope ratio mass spectrometer; CO2 equil. - water-CO2 equilibration technique; Zn red. to H2 - zinc reduction method; Cr red. to H2 - chromium reduction method; LAS - laser absorption spectroscopy; H2 equil. - water-H2 equilibration technique; GPC -gas proportional counting; LSC-EE - electrolytic enrichment liquid scintillation counting; filt. 589/1 - sample filtered through Grade 589/1; filt. 589/3 - sample filtered through Grade 589/3; n.d. - not determined, n.r. - not reported. For sampling collectors see Figure 2. 72 Polona VREČA & Neža MALENŠEK Table 2. Sampling and analytical methods - continued. Location Sampling collector Sample bottles and analytical methods References ¿■"O (f2H 3H 16 Sinji vrh c n.r. n.r. n.d. Trček, 2003 17 Sela na Krasu b HDPE IRMS CO2 equil. HDPE IRMS Cr red. to H2 n.d. Doctor, 2002 18 Selniška Dobrava c b-pl. IRMS CO2 equil. b-pl. IRMS Cr red. to H2 n.d. Mali, 2006, Mali & Urbanc, 2009 19 Union brewery, Ljubljana n.r. n.r. n.r. n.d. Trček, 2005, 2006 20 Postojna cave c n.r. n.r. n.d. Kogovšek & Urbanc, 2007 21 Rogaška Slatina n.r. n.r. n.r. n.r. Trček & Leis, 2011 22 Postojna Karst Research Institute d n.r. n.d. n.d. Mandič, 2013 23 Ilirska Bistrica d IRMS CO2 equil. IRMS H2 equil. n.d. Mance et al., 2014 24 Snežnik d IRMS CO2 equil. IRMS H2 equil. n.d. Mance et al., 2014 Lapanje (2000), and at the Karst Research Institute in Postojna (ZRC SAZU) from June 2010 to February 2011 by Mandic (2013). Detailed data (i.e. coordinates) about these locations are not reported. The monitoring of tritium in precipitation, surface and groundwater is performed at other locations in Slovenia in the frame of national programmes approved by the Slovenian Nuclear Safety Administration (Kovacic, 2015 and references therein). Results of these investigations are not discussed in this paper. To summarize, isotope composition of monthly precipitation was monitored in the period 19812015 at 30 different locations in Slovenia, however none of the monitoring operated continuously at the same location during the last 35 years. Data about sampling and analytical methods used for determining isotope composition (c>18O, c>2H and 3H, if measured) are summarized in Tables 1 and 2 while the mean isotope values and LMWLs are presented in Table 3. Sampling of precipitation for isotope analysis in Slovenia Basic data about 26 locations are summarized in Table 1, which includes all available information like coordinates, sampling period, type of sampling station and GNIP code in case that the station is already or will be included in the worldwide database. Information about type of sampling collector and water sample treatment (filtration, types of storage bottle used) are presented in Table 2. The 15 locations with known coordinates (except Murska Sobota) are shown in Figure 1 and different types of sampling collectors are presented schematically in Figure 2. The longest isotope record is available for Ljubljana (Fig.1, Tab. 1) and is maintained by the staff of the Department of Environmental Sciences of the JSI. Samples are collected from the precipitation collector (type a in Fig. 2) as soon as possible after the precipitation event (Vreča et al., 2014). Many stations (Fig. 1, Tab. 1) are part of the Slovenian national meteorological network maintained by the staff of ARSO where precipitation samples are collected from the collector (type b in Fig. 2, Tab. 2) either three times (synoptic stations) or once per day (climatological and precipitation stations). Details about sampling at Selniška Dobrava are described in Mali (2006). They collected precipitation from a system connected by a tube to a glass bottle (type c in Fig. 2). Similar collectors with an isolated vessel buried in the soil were used at Sinji vrh (Trček, 2003), at the Postojna cave (Kogovšek & Urbanc, 2007) and at four stations maintained by the GeoZS (Urbanc, personal communication). The high-density polyethylene (HDPE) collectors containing paraffin oil to prevent evaporation during sampling were used at four locations (Fig. 2d, Tab. 2), at Portorož until 2002 (Vreča et al., 2011), at Sela na Krasu (Doctor, 2002) and at Ilirska Bistrica and Snežnik (Mance et al., 2014). The collected water was separated from the oil at the end of the month. At Postojna (Mandič, 2013) Slovenian Network of Isotopes in Precipitation (SLONIP) - a review of activities in the period 1981-2015. 73 Fig. 2. Different types of collectors used for sampling of precipitation in Slovenia. a - collector used at Jožef Stefan Institute, b - collector used at meteorological stations, c -buried totalizer, d - totalizer with paraffin oil layer. Schematic presentations of type b, c and d collectors kindly provided by S. Terzer, IAEA. precipitation was sampled also on the roof of the ZRC SAZU and integrated monthly samples were collected in a HDPE container with added paraffin oil. Walls of the collector were completely covered with aluminium foil and Styrofoam to achieve temperature stability and to prevent growth of algae. According to IAEA guidelines (Internet 3) approximately 0.5 cm film of paraffin is recommended. However, a thicker paraffin layer (approximately 1 cm) will be recommended in updated guidelines as shown schematically for sampling collector type d in Figure 2 (Terzer, personal communication). In Velenje HDPE collector was used (Kanduč et al., 2014). For Kleče, Blatnik, Ponikve, the Union brewery and Rogaška Slatina details about how the samples were collected are not given. At the laboratory impurities (e.g. dust, particles) were removed from the samples collected at the stations Ljubljana-Reaktor, Portorož, Kredarica, Rateče, Bohinjska Češnjica, Zgornja Radovna and Podljubelj by filtration through 12-25 ^m pore size ashless filter papers (Grade 589/1 Black Ribbon, Whatman, UK) before taking aliquots for the different isotope analyses (Vreča et al., 2014, 2015a). Zavadlav (2013) reports filtration of samples through 2 ^m pore size ashless filters (Grade 589/3, Whatman, UK). For other sampling stations filtration of samples is not reported. Samples were stored either in polyethylene, HDPE or in borosilicate glass bottles (Tab. 2). Analytical methods used for determining stable oxygen (c>18O) and hydrogen (c>2H) isotope composition Oxygen isotope composition (c>18O) was determined at all locations and in all cases the c>18O was measured using the water-CO2 equilibration technique (Epstein & Mayeda, 1953; Avak & Brand, 1995, Tab. 2). However, different IRMS were used including either a dual inlet Varian MAT 250 at JSI (Urbanc & Jamnik, 1999; Pezdič, 1999; Lapanje, 2000; Vreča et al., 2008, 2011), Finnigan DELTAplus at the Joanneum Research (JR) in Graz, Austria (Mali, 2006; Mandič, 2013; Vreča et al., 2008, 2011), Thermo Finnigan DELTAplus XP at the University of Rijeka (UR), Croatia (Mance et al., 2014) or a continuous flow IsoPrime IRMS at the JSI (Lojen, personal communication; Zavadlav, 2013; Zavadlav et al., 2012; Vreča et al., 2013, 2014, 2015a; Vreča, 2015). Doctor (2002) and Trček (2003, 2005, 2006) report that analyses were performed at the Institute of Groundwater Ecology (GSF) in Neuherberg, Germany but do not state the type of IRMS used for analysis. Kogovšek & Urbanc (2007), Trček & Leis (2011) report just that analyses were performed at the JR in Graz, Austria and Kanduč et al. (2014) at the National Institute of Geophysics and Volcanology (INVG) in Palermo, Italy. Investigations at Murska Sobota started in 2015 and sample analysis is in progress at the JSI. Samples collected by the GeoZS at four locations around Slovenia were analysed at the JSI (Urbanc, personal communication). For certain samples (Tab. 2), c>18O was determined by off-axis integrated cavity output laser absorption spectroscopy (LAS) (OA-ICOS, Los Gatos Research, Mountain View CA, United States of America) at the IAEA Isotope Hydrology Laboratory (IHL) in Austria according to the analytical protocol of Wassenaar et al. (2014). Hydrogen isotope composition (c>2H) was determined at 25 locations using different analytical methods. These included H2 generated by reduction of water over hot zinc - Zn (Pezdič, 1999), reduction of water over hot chromium -Cr (Gehre et al., 1996; Morrison et al., 2001) or by water-H2 equilibration using platinum - Pt 74 Polona VREČA & Neža MALENŠEK (Horita et al., 1989; Coplen et al., 1991, Tab. 2). Measurements were performed on different IRMS like the dual inlet Varian MAT 250 at JSI (Pezdič, 1999; Vreča et al., 2008, 2011) or the Finnigan DELTAplus XP at the JR (mali, 2006; Vreča et al., 2008, 2011, 2014, 2015a) and at the UR (Mance et al., 2014). Doctor (2002) reports that the chromium reduction method (Gehre et al., 1996) was used at the GSF, however similar as in Trček (2003, 2005, 2006) no information about the type of IRMS used for analysis is reported. Kogovšek & Urbanc (2007) and Trček & Leis (2011) report just that the analyses were performed at JR in Austria, while Kanduč et al. (2014) report that analyses were performed at the INVG. Investigations at Murska Sobota started in 2015 and sample analysis is in progress at the JSI. Samples collected by GeoZS at four locations around Slovenia are analysed at the JSI (Urbanc, personal communication). For certain samples (Tab. 2), ¿2H was determined also by LAS at IAEA IHL according to the analytical protocol of Wassenaar et al. (2014). Results are reported as d values in per mill (%0) relative to the Vienna-SMOW standard (Coplen et al., 2002). Methods used in different laboratories are described in more detail in Pezdič (1999), Mali (2006) and Mandič (2013). The authors usually report that measurements were carried out together with laboratory standards calibrated periodically against international standards, as recommended by the IAEA and that the measurement precision was better than ±0.1 %o for ¿18O and ±1 %o for ¿2H. In some cases, better precision was reported (e.g. Trček & Leis, 2011). Analytical methods used for determining tritium activity (3H) if available together with stable isotope data Tritium activity was monitored in the frame of SLONIP activities only at 11 locations (Tab. 2). Analyses of samples from Ljubljana, Portorož and Kozina were performed at the RBI either by the gas proportional counting (GPC) technique (Krajcar Bronič et al., 1998; Vreča et al., 2006, 2008, 2011 and references therein) or by the liquid scintillation counting technique (LSC) following electrolytic enrichment (EE) (Vreča et al., 2014, 2015a and references therein). In samples collected in the second half of 2003 in Ljubljana, Portorož and Kozina, 3H activity was determined at the IHL after EE by the LSC technique (Vreča et al., 2006) while samples collected after 2010 were analysed after EE by LSC at the JSI (Vreča et al., 2014, 2015a, 2015b). Trček & Leis (2011) report only that 3H measurements were performed in the Isotope laboratory HYDROSYS in Hungary. Meteorological data The most rational approach for monitoring isotopes in precipitation is to perform sampling at meteorological stations that are part of a national network such as the Swiss National Network for the observation of Isotopes in the Water Cycle - NISOT (Schurch et al., 2003). Therefore, the JSI cooperates with the staff of ARSO meteorological stations where meteorological data like precipitation and air temperature, are available from the ARSO database (Internet 4). We performed in the past isotope monitoring at 11 different ARSO stations (Tab.1, Fig. 1) and since 2015 sampling has been performed at six ARSO stations (Tab. 1). Unfortunately, air temperature data were not available for the majority of isotope monitoring stations including the ARSO precipitation stations: Sela na Krasu, Kozina, Dvor, Zgornja Radovna and Podljubelj, and therefore it was not possible to determine the relation between isotope composition and temperature. Precipitation data in numerical form (expressed in mm) for other than ARSO stations, except precipitation for Ljubljana-Reaktor (Vreča et al., 2014) are not reported. However, precipitation data are presented graphically by Trček (2003, 2006), Kogovšek & Urbanc (2007), and Mali & Urbanc (2009). Data reduction Most publications report basic descriptive statistics (mean ¿18O, ¿2H) while deuterium excess (d-excess) as defined by Dansgaard (1964) is not always calculated and reported. Even less publications report values weighted by the amount of precipitation and consequently the influence of precipitation amount at a particular location is not determined. As recommended by the IAEA (1992), the summations have to be calculated over all collected samples per year and per month over the period. The minimum required number of data is eight monthly measured samples per year and more than 70 % of total precipitation collected per year. For example, in Selniška Dobrava (Mali, 2006) these requirements were not fulfilled, many monthly data are missing and therefore caution is needed in future calculations and interpretations. Reporting isotope data, mean isotope values and local meteoric water lines Numerical data are evaluated and published for Ljubljana and Portorož until the end of 2010, and for the period 2011-2015 evaluation of the data is in progress. For Sela na Krasu (Doctor, 2002), Kozina (Vreča et al., 2005; GNIP database), Selniška Dobrava (Mali, 2006) and Velenje Slovenian Network of Isotopes in Precipitation (SLONIP) - a review of activities in the period 1981-2015. 75 (Kanduč et al., 2015) data are reported for the whole sampling period, while for Dvor only oxygen data for 2009 - 2010 are reported (Zavadlav, 2013). Evaluation of data collected by the JSI for the stations Kredarica, Rateče, Bohinjska Češnjica, Zgornja Radovna, Podljubelj, Dvor and Postojna for the whole sampling period is in progress. Figure 3 shows the number of evaluated or partly evaluated data for Ljubljana and the different regions of Slovenia. In the eastern part of the country, there is a deficiency of numerical data and the new data from Murska Sobota will help fill this data gap for NE part of the country. Arithmetic and weighted means together with LMWLs as reported in publications are presented in Table 3. Complete data are only available for Ljubljana, Portorož and Kozina. Mean isotope composition of oxygen and hydrogen together with d-excess are reported for 13 locations, while tritium and weighted mean values are reported only rarely (Tab. 3). Arithmetic or weighted means can be further used for geostatistical evaluation of the data and modelling the geospatial distribution of water isotopes in precipitation. Vreca et al. (2010) reported the first presentation of such a map for oxygen isotope composition of precipitation over Slovenia in 2010. The spatial distribution of ¿18O in precipitation has been explained by a simple multiple regression model, based on the meteorological (temperature) and geographic factors (latitude and elevation) and a continuous digital map of the ¿18O distribution over Slovenia has been generated using GIS tools. Further evaluations of the data are in progress and will take into account data collected during the last 35 years. The review shows that the data sets, available for Slovenia during the same period, do not always overlap and therefore in spatial modelling, these gaps, have to be taken into account adequately. This is particularly important in the preparation of reliable geospatial maps and in their future implementation in water resources research, food authentication and other applications in Slovenia. Authors report rarely local meteoric water lines (LMWL) and only in a few cases details about regression analysis are given (Tab. 3, Vreča et al. 2008, 2011, 2014, 2015a). For Ljubljana many different LMWLs are reported but users have to be aware of the details about different lines which are all close to the Global Meteoric Water Line (GMWL) defined by Craig (1961). Differences among the LMWLs are due to the different observation periods, number of data, or the type of regression calculations. These factors should be Fig. 3. Number of oxygen (¿18O), hydrogen (¿2H) and tritium (3H) monthly data evaluated for Ljubljana (LJ) and different regions of Slovenia: south-western (SW - locations 2, 3 and 17 in Table 1), north-western (NW - locations 6 to 9 in Table 1), northern (N -location 10 in Table 1), north-eastern (NE - locations 11 and 18 in Table 1) and south-eastern (SE - location 4 in Table 1) part of Slovenia. Table 3. Local meteoric water lines (LMWLs), arithmetic and weighted mean isotope values. LSF - least squares fit, RMA -reduced major axis regression (called also orthogonal regression), OLSF - ordinary least square regression, PWLSR - precipitation weighted least square regression, *- calculated from the available numeric data, n.d. - not determined, n.r. - not reported. Location Sampling period LMWL Arithmetic mean Weighted mean References si8o (%o) S2H (%o) d (%o) 3H (TU) si8o (%o) S2H (%o) d (%o) 3H (TU) Ljubljana n.r. r = 0.99, n = 90 S2H = (8.197 ± 0.276)x5180 + (10.834 ± 2.468) -8.5 -60 n.r. n.r. n.r. n.r. n.r. n.r. Pezdič, 1999 Ljubljana 1982-1994 r = 0.99, n = 90 S2H = 8.83xS180 + 16.5 n.r. n.r. n.r. n.r. -8.73 -60.6 n.r. n.r. Pezdič, 2003 Ljubljana 1981-1996 r = 0.99, n = 149 S2H = (8.1 ± 0.1)xS180 + (11.1 ± 0.8) -9.3 n.r. n.r. n.r. n.r. n.r. n.r. n.r. Krajcar Bronič et al., 1998 Ljubljana 1981-2006 LSF: r = 0.99, n = 290 S2H = (7.95 ± 0.08)xS180 + (8.90 ± 0.71) -8.7 n=290 -60 n=290 9.4 n=290 16.4 n=264 -8.57 n=290 -59.1 n=290 9.5 n=290 n.d. Vreča et al., 2008 # - period 1998-2006 RMA: r = 0.99, n = 290 S2H = (8.06 ± 0.08)xS180 + (9.84 ± 0.71) 9.3 n=92# Ljubljana 2001-2003 RMA: r = 0.99, n = 36 S2H = (8.0 ± 0.2)x5180 + (9.2 ± 1.8) -8.3 n=36 -57 n=36 9.3 n=36 8.1 n=35 -8.1 n=36 -55 n=36 10.3 n=36 8.0 n=35 Vreča et al., 2006 Ljubljana 2007-2010 OLSF: r = 0.98, n = 46 52H = (8.05 ± 0.22)x5180 + (10.36 ± 2.02) -8.6 n=46 -59 n=46 9.9 n=46 8.3 n=45 -8.7 n=46 -59 n=46 10.3 n=46 8.5 n=45 Vreča et al., 2014 RMA: r = 0.98, n = 46 S2H = (8.19 ± 0.22)x5180 + (11.52 ± 1.97) PWLSR: r = 0.99, n = 46 S2H = (7.94 ± 0.21)xS180 + (9.76 ± 1.91) Portorož airport 2001-2003 RMA: r = 0.96, n = 35 S2H = (7.7 ± 0.4)x5180 + (7.3 ± 2.2) -5.8 n=35 -38 n=35 9.2 n=35 6.9 n=34 -6.3 n=35 -40 n=35 10.3 n=35 6.3 n=34 Vreča et al., 2006 o o 3 a: < W H r> > 3 > r1 H CO. H W Slovenian Network of Isotopes in Precipitation (SLONIP) - a review of activities in the period 1981-2015. 77 References Vreča et al., 2011 Vreča et al., 2015a Vreča et al., 2015a Vreča et al., 2006 Vreča et al., 2007 Vreča, 2015 Vreča et al., 2015b Weighted mean 3 5 m ^h on c^ m3 II g 6.4 n=47 5.4 n=33 7.9 n=36 7.6 n=35 6.8 n=33 7.3 n=34 7.6 n=34 00 c^ c* Il g 8.6 n=47 12.2 n=36 n.d. n.d. n.d. n.d. n.d. S2H (%») S " ¡k -41.6 n=47 -50 n=36 n.d. n.d. n.d. n.d. n.d. S18O (%o) ^ £ il 1 s -6.28 n=47 -7.8 n=36 n.d. n.d. n.d. n.d. n.d. Arithmetic mean 3 2 > 3 > r1 H S co. H W Slovenian Network of Isotopes in Precipitation (SLONIP) - a review of activities in the period 1981-2015. 79 o ^ o 5 8 "3 S3