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Between 1979 and 2003, a 35 cm thick layer of laminated tufa formed around a wooden pillar located at the beginning of the Korana River, which emerges from the Plitvice Lakes, Croatia. The laminated tufa structure allowed for the stratigraphic analysis of mineral, elemental and δ18O and δ13C isotope composition. Results are compared to other carbonate archives (lake sediments) from the Plitvice Lakes and to measured water physical–chemical data collected in the same time. An increase in water temperature and decrease in Mg/Ca ratio was observed during that period. Results showed that the tufa Mg/Ca ratio and δ18O could not be used as a temperature proxy, while an observed δ18O increase after 1990 was attributed to increase in evaporation rate. Furthermore, the constant increase in redox-sensitive elements (Mn) towards the external part of tufa may indicate periodic events of anoxia at the sediment/water interface. Local enrichment factors (LEFs) for potentially toxic elements were calculated using the background function and Al as the normalizing element. The LEFs showed an enrichment pattern of Cu and Pb in 1983 and 2001, which could indicate their anthropogenic origin and the sensitivity of the tufa to environmental changes.

Tufa is a fresh-water surface calcium carbonate deposit precipitated at or near ambient temperature, and commonly contains the remains of macro- and microphytes. Many Holocene tufas are found along the Zrmanja River, Dalmatian karst, Croatia. In this work we present radiocarbon dating results of older tufa that was found for the first time at the Zrmanja River near the Village of Sanaderi. Tufa outcrops were observed at different levels, between the river bed and up to 26 m above its present level. Radiocarbon dating of the carbonate fraction revealed ages from modern, at the river bed, up to 40 kBP ~20 m above its present level. These ages fit well with the hypothesis that the Zrmanja River had a previous surface connection with the Krka River, and changed its flow direction toward the Novigrad Sea approximately 40 kBP (Marine Isotope Stage 3). Radiocarbon AMS dating of tufa organic residue yielded a maximum conventional age of 17 kBP for the highest outcrop position indicating probable penetration of younger organic material to hollow tufa structures, as confirmed by radiocarbon analyses of humin extracted from the samples. Stable carbon isotope composition (δ13C) of the carbonate fraction of (−10.4 ± 0.6)‰ and (−9.7 ± 0.8)‰ for the Holocene and the older samples, respectively, indicate the autochthonous origin of the carbonate. The δ13C values of (−30.5 ± 0.3)‰ and (−29.6 ± 0.6)‰ for organic residue, having ages &lt, 500 BP and &gt, 5000 BP, respectively, suggest a unique carbon source for photosynthesis, mainly atmospheric CO2, with an indication of the Suess effect in δ13C during last centuries. The oxygen isotopic composition (δ18O) agrees well with deposition of tufa samples in two stages, the Holocene (−8.02 ± 0.72‰) and “old” (mainly MIS 3 and the beginning of MIS 2) (−6.89 ± 0.34‰), suggesting a ~4 °C lower temperature in MIS 3 compared to the current one.

Prirodna ravnotežna 14C aktivnost u atmosferskom ugljikovu dioksidu i u biosferi narušena je na globalnoj razini ljudskom djelatnošću. Intenzivni termonuklearni atmosferski pokusi sredinom 20. stoljeća uzrokovali su naglo povišenje 14C aktivnosti u atmosferi na razinu gotovo dvostruko višu od prirodne, a nakon zabrane pokusa 14C aktivnost se smanjuje i danas je gotovo dosegla prirodnu ravnotežnu vrijednost. U ovom su radu prikazani rezultati praćenja 14C aktivnosti u atmosferskom CO2, godovima drveća i biološkim uzorcima na nekoliko karakterističnih lokacija na području Hrvatske i Slovenije. Globalne promjene 14C aktivnosti opažaju se i na “čistim” lokacijama u zaštićenim područjima. U urbanim sredinama opažaju se lokalni efekti sniženja 14C aktivnosti u atmosferi zbog povećanog izgaranja fosilnih goriva, što je posebno izraženo u zimskim mjesecima. U okolici nuklearne elektrane opaža se povišenje 14C aktivnosti u atmosferskom CO2 za vrijeme i neposredno nakon izmjene gorivih elemenata, a ako se remont provodi početkom vegetacijskog razdoblja, tada se opaža povišena 14C aktivnost i u biljkama iz neposredne okolice., The natural equilibrium of 14C activity in atmospheric CO2 and in the biosphere has been disturbed globally by various anthropogenic activities. Intensive atmospheric thermonuclear bomb tests in the mid 20th century doubled the natural 14C activity in the atmosphere. Since the bomb test ban, this activity has constantly been decreasing and has almost reached its natural level. This article presents the results of 14C activity monitoring in atmospheric CO2, tree rings and biological samples at several locations in Croatia and Slovenia. Global changes in 14C activity have been observed at “clean-air” sites. In urban areas, lower atmospheric 14C activity is owed to intense fossil fuel combustion, especially in the winter. Higher 14C activity is observed in near the nuclear power plant during and immediately after refuelling outage. If refuelling is performed in the spring, when plants start to vegetate, increased 14C activity is also refl ected on them.