• Environmental 14C Levels Around the 632 MWe Nuclear Power Plant Krško in Yugoslavia

      Obelić, Bogomil; Krajcar-Bronić, Ines; Srdoč, Dušan; Horvatinčić, Nada (American Journal of Science, 1986-01-01)
      Measurements of 14C activity of atmospheric CO2, vegetables, and tree rings in the area of the 632 MWe power plant Krško in Slovenia, NW Yugoslavia, have been in progress since January, 1984. Sampling stations are located in the area ca 400km2 and are distributed in the direction of the prevailing westerly winds. The closest sampling point is 1.5km NE of the plant exhaust stack, the farthest sampling point is 30km E of the plant. A sampling site at National Park Plitvice in central Croatia was chosen as the 14C reference point not affected by the power plant. An average excess of 2.2% above the reference point activity during normal periods of reactor operation was observed 1.5km from the plant smokestack. Calculations of the 14C release from the power plant was estimated at 0.1 TBq/a. The tree ring activity near the plant followed the 14C activity of the Northern Hemisphere in the past decade. No influence of the power plant release was observed on the tree ring activity.
    • Increase of 14C Activity of Dissolved Inorganic Carbon Along a River Course

      Srdoč, Dušan; Krajcar-Bronić, Ines; Horvatinčić, Nada; Obelić, Bogomil (American Journal of Science, 1986-01-01)
      Results of measurements for 3 years (1981-1983) of 14C activity of dissolved inorganic carbon (DIC) in water samples from the Korana River, as well as that of recent tufa and aquatic plants, showed that 14C concentration increases from karst spring to the estuary. A model describing the increase of 14C activity was developed assuming that the increase is due to the exchange of the dissolved CO2 in stream water with atmospheric CO2 and to dissolution of CO2 from the decay of organic material and root respiration. It is possible to distinguish these two contributions by measuring the delta-13C values of DIC in water. As expected, our data show that the exchange process between atmospheric CO2 and DIC dominates at rapids and waterfalls, while biologic contribution is much higher in lakes and along the lowland flow of the Korana River. Agreement between the calculated and the measured activities supports the proposed mechanisms of chemical and isotopic exchanges in stream waters.
    • On the Initial 14C Activity of Karst Aquifers with Short Mean Residence Time

      Krajcar-Bronić, Ines; Horvatinčić, Nada; Srdoč, Dušan; Obelić, Bogomil (American Journal of Science, 1986-01-01)
      The 14C activity of total dissolved inorganic carbon (DIC) as well as tritium activity and stable isotope content (13C, 2H, 18O) of spring water were measured for 3 consecutive years at 3 karst springs that feed Plitvice Lakes, NW Yugoslavia. The constant chemical and stable isotope composition and temperature indicated well mixed aquifers. A very short mean residence time of underground water (2-5 yr) was determined by tritium activity measurements. Measured 14C activities of 3 karst springs varied from 60.0% to 82.5%. The measured 14C activities were compared with calculated 14C activities based on various models using measured values of 14C activity of soil at different depths and 13C content of limestone, plants, and soils from the recharge area. Our measurements indicate that recharge systems in karst aquifers are open to the atmosphere. The atmospheric CO2 contributes to the 13C content and the 14C activity of ground water to an estimated extent which varies between 10 and 40% of DIC.
    • Radiocarbon Dating of Lake Sediment from Two Karst Lakes in Yugoslavia

      Srdoč, Dušan; Obelić, Bogomil; Horvatinčić, Nada; Krajcar-Bronić, Ines; Marčenko, Elena; Merkt, Joseph; Wong, How Kin; Sliepčević, Adela (American Journal of Science, 1986-01-01)
      Samples of sediment cores from two lakes in the karst area of northwest Yugoslavia were analyzed. Both Lakes Kozjak and Prošće are in the Plitvice National Park, Central Croatia. 14C dating, sedimentologic, seismic, and isotopic studies, and distribution of diatoms are presented. 14C dating of lake marl revealed a uniforn sedimentation rate in Lake Prošće as opposed to Lake Kozjak. Both lake sediments belong to the Holocene period. 14C dating of lake sediment is in agreement with seismic profiles, sedimentologic analysis, and diatom frequency measurements both in an undisturbed as well as in a disturbed lake sediment.