engleski

CARBON ISOTOPE DISTRIBUTION IN THE KARST AREA

Distribution of carbon isotopes 14C (a14C) and 13C (δ13C) was investigated in the Dinaric karst area of Croatia. As a case study we used Plitvice Lakes National Park which is a typical karst area with karst springs, lakes and rivers, recent carbonate deposits in form of tufa and lake sediments, terrestrial and aquatic plants, as well as a soil above the limestone bedrock. Recent environmental samples were collected in 2011-2012 in the whole area of the National Park including: atmospheric CO2, spring, lake and river waters, water profile in the lakes, surface soil, terrestrial plants (deciduous and conifer), aquatic plants (partly or completely submerged) and recent lake sediments (carbonate and organic fraction). The anthropogenic 14C in the atmosphere due to nuclear bomb-tests in early 1960s has been reflected also in the protected area of the Plitvice Lakes National Park (Krajcar Bronić et al. 1998, Horvatinčić et al. 2008). a14C values measured in the recent environmental samples are close to the pre-bomb natural a14C, i.e. before 1950. a14C values of atmospheric CO2, terrestrial plants and soil range between100 and 110 pMC which is similar to the present a14C in the global atmosphere. a14C and δ13C values of surface water (dissolved inorganic carbon, DIC) and aquatic plants depend on the processes involved in the carbon cycle, i.e. geochemical processes of carbonate dissolution and precipitation, photosynthetic process and carbon isotope exchange between atmospheric CO2 and DIC in water. It was observed that a14C and δ13C values of water profile were influenced by seasonal changes and thermal stratification. The a14C bomb peak was reflected in lake sediment layers, in both carbonate and organic fraction, but with damped and delayed response. The intensity of the bomb peak reflection decreases with increasing lake depth. Comparison of the a14C values obtained 30 years ago at the Plitvice Lakes area with recent measurements presented in this work showed that almost all carbon pools of the Plitvice Lakes karst area were influenced by nuclear bomb 14C contamination, but the intensity depends on the processes introducing carbon from the atmosphere. Horvatinčić N, Barešić J, Babinka S, Obelić B, Krajcar Bronić I, Vreča P, Suckow A. Towards a deeper understanding how carbonate isotopes (14C, 13C, 18O) reflect environmental changes: A study with recent 210Pb-dated sediments of the Plitvice Lakes, Croatia. Radiocarbon 2008 ; 50: 233-253. Krajcar Bronić I, Horvatinčić N, Obelić B. Two decades of environmental isotope record in Croatia: reconstruction of the past and prediction of future levels. Radiocarbon 1998 ; 40:399-416.

carbon isotopes; karst; Plitvice Lakes

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