ABSTRACT
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 â 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.
ABSTRACT
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 â¼30% 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 â¼ 0â % 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.
