Can we see differences between the 14C activities of urban (Zagreb) and rural (Cvetkovic) sites (central Croatia)?

Radiocarbon (Δ14C) was measured for four years (2019-2022) in Zagreb (Croatia) and in Cvetkovic village near Jastrebarsko (Zagreb County, Croatia) to see whether there are differences between the city site and the rural one because of the fossil fuel combustion. The δ13CCO2 was measured as grab samples once in a month in period December 2020-November 2022. The bomb-produced 14C has been globally distributed across the planet, but the combustion of fossil fuels that do not contain 14C causes a local effect of lowering Δ14C. Zagreb is considered to be a location with heavy fossil fuel combustion as compared to the Cvetkovic (rural site). Monthly 14C activity at Zagreb is constantly below the 14C activity at Cvetkovic. Mean 14C activity at Zagreb (Δ14CZagreb = -18.4 ± 2.6 ‰) is lower than that in Cvetkovic (Δ14CCve = -2.9 ± 2.1 ‰) due to fossil fuel combustion in the city of Zagreb. This is especially pronounced during winter when the mean value in Zagreb is Δ14CZagreb = -26.0 ± 4.3 ‰ and in Cvetkovic Δ14CCve = -5.9 ± 3.4 ‰. Natural gas consumption was used as the proxy for fossil fuel combustion, and it shows better correlation with Δ14C in Zagreb than in Cvetkovic. The Δ14C difference, Δ14CCve ‒ Δ14CZagreb, becomes statistically negligible when natural gas consumption is small. No difference is observed on δ13CCO2; in Zagreb mean δ13CCO2 is -11.0 ± 1.3 ‰, and in Cvetkovic -11.4 ± 1.4 ‰. Lower δ13CCO2 values are observed in winter (Zagreb -11.9 ± 1.1 ‰, -12.2 ± 1.5 ‰ Cvetkovic) than in summer (-10.1 ± 0.8 ‰ vs. -10.4 ± 1.0 ‰) at both locations. Together with higher Δ14C in Cvetkovic, it indicates that at the area of Cvetkovic biogenic samples of modern origin (biomass, wood) as energy source for heating is more pronounced.

Carbon isotope fractionation in karst aquatic mosses.

Radiocarbon activity (a14C) and 13C composition (δ13C) were measured in hygrophyte and mesophyte (land) mosses collected in the natural habitat of the Plitvice Lakes and along the Zrmanja and Krupa Rivers (typical continental and Mediterranean climates, respectively), Croatia. a14C and δ13C values of mosses, of atmospheric CO2 and dissolved inorganic carbon (DIC) were compared with contemporary data and with data from 30 years ago at the Plitvice Lakes when 14C activity of atmospheric CO2 was ∼30% higher. A positive correlation between a14Cmoss and δ13Cmoss was observed for all data reflecting the change of carbon isotopic composition in DIC along the water flows and in atmospheric CO2 regardless of the climatic regions and historic period. Fraction of the atmospheric carbon in moss (ωatm.C) and carbon fractionation factor from aquatic CO2 (DIC) to moss tissue (εmoss/g-aq) were calculated for each individual moss. Three species of mosses had ωatm.C ∼ 0 % implying that they turn to anabiosis during dry periods. The relation εmoss/g-aqvs.ωatm.C differentiates true aquatic and amphiphyte mosses. The first had a statistically significant negative correlation between εmoss/g-aq and ωatm.C. The amphiphyte mosses had lower εmoss/g-aq with higher water flow rates.

Carbon isotopic composition (δ(13)C and (14)C activity) of plant samples in the vicinity of the Slovene nuclear power plant.

δ(13)C values of various plants (apples, wheat, and maize) collected in the vicinity of the Krsko Nuclear Power Plant (Slovenia) during 2008 and 2009 were determined. By measuring dried samples and their carbonized counterparts we showed that no significant isotopic fractionation occurs during the carbonization phase of the sample preparation process in the laboratory. The measured δ(13)C values of the plants were used for δ(13)C correction of their measured (14)C activities.

Stable isotope composition of daily and monthly precipitation in Zagreb.

Stable isotopic compositions (delta2H and delta18O) of daily precipitation collected in the period from October 2002 to March 2003 and monthly precipitation in the period from 2001 to 2003, as well as the corresponding meteorological data (temperature, amount of precipitation), all collected in Zagreb, Croatia, are presented. delta2H and delta18O values, both daily and monthly, show large variations due to large temperature variations and the different origin of the air masses. Variations are larger for daily samples than for composite monthly samples. Good correlation of delta18O with temperature is obtained for both types of samples. On the basis of the correlation between delta2H and delta18O, the local meteoric water line is close to the global meteoric water line. Deuterium excess of both daily and monthly precipitation indicates that in the Zagreb area, the influence of air masses from the Mediterranean area prevails in the autumn period.

Distribution of hydrogen, oxygen and carbon isotopes in the atmosphere of Croatia and Slovenia.

Monitoring of isotope distribution in the atmosphere included isotopes 2H, 3H and 18O in precipitation, and 13C and 14C in atmospheric CO2. This paper presents the results of atmospheric monitoring over Croatia and Slovenia overt the last few years. Monthly precipitations in Zagreb and Ljubljana had been collected since 1976 and 1981, respectively. Between 2000 and 2003 monitoring also included seven stations along the Adriatic coast. Tritium activity in precipitation shows seasonal variations that were most pronounced inland (at the continental stations Zagreb and Ljubljana) and were the smallest in the south Adriatic (Komiza and Dubrovnik). Mean annual tritium activity decreases from the north to the south Adriatic coast. Seasonal variations in delta2H and delta18O in precipitation follow the temperature variations at the sampling stations. Atmospheric CO2 was collected in Zagreb and Plitvice as a composite monthly sample. Both delta14C and delta13C showed seasonal variations. The mean annual 14C activities in Zagreb had been decreasing after the peak reached in the 1960s, and for the last three years the mean 14C activity (delta14C) remained about 30 per thousand.