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Three types of recent carbonate precipitates from the River Krka, Croatia, were analysed: (1) bulk tufa from four main cascades in a 34 km long section of the river flow through the Krka National Park; (2) a laminar stromatolite-like incrustation formed in the tunnel of a hydroelectric power plant close to the lowest cascade; and (3) recent precipitates collected on artificial substrates during winter, spring and summer periods. Stable isotope compositions of carbon (d 13 C) and oxygen (d 18 O) in the carbonate and organic carbon (d 13 C org ) were determined and compared with d 18 O of water and d 13 C of dissolved inorganic carbon (DIC). The source of DIC, which provides C for tufa precipitation, was determined from the slope of the line ( (Sayles & Curry, 1988). The d 13 C value of added DIC was )13AE6&, corresponding to the dissolution of CO 2 with d 13 C between )19AE5 and )23AE0& Vienna Pee Dee Belemnite (VPDB). The observed difference between the measured and calculated equilibrium temperature of precipitation of bulk tufa barriers indicates that the higher the water temperature, the larger the error in the estimated temperature of precipitation. This implies that the climatic signals may be valid only in tufas precipitated at lower and relatively stable temperatures. The laminar crust comprising a continuous record of the last 40 years of precipitation shows a consistent trend of increasing d 13 C and decreasing d 18 O. The lack of covariation between d 13 C and d 18 O indicates that precipitation of calcite was not kinetically controlled for either of the elements. d 13 C and d 18 O of precipitates collected on different artificial substrates show that surface characteristics both of substrates and colonizing biota play an important role in C and O isotope fractionation during carbonate precipitation.

Regular 14C sampling of discharged air began in 1988 at Paks Nuclear Power Plant (NPP), Hungary, and in 1991 at NPPs in Krsko, Slovenia and Bohunice, Slovakia. Monitoring of 14C discharges is carried out at all NPPs with similar differential samplers continuously collecting 14C in the form of 14CO2 and 14CnHm. The main results of airborne discharge monitoring are as follows: 14C activity concentration varied roughly within a factor of two around their mean values, 125 Bq m-3 and 90 Bq m-3 for Paks and for Krsko NPP, respectively. The pattern of discharge for Bohunice NPP is slightly different from that at the other two stations. At Bohunice, there has been a continuous increase in the discharge rate at power unit V1, starting with 70 Bq m-3 in 1991 and reaching a value of 190 Bq m-3 in 1995. The values for power unit V2 are 50 Bq m-3 and 82 Bq m-3. The average normalized yearly discharge rates are 0.887 (TBqGWe-1yr-1) for Paks, 0.815 (V1) and 0.500 (V2) for Bohunice, and 0.219 for Krsko. Most of the discharged 14C is in hydrocarbon form, 95% for Paks and Bohunice V2, but the CO2 fraction may reach 25% or 43% at Bohunice V1 and Krsko, respectively. At Bohunice V1, not only the discharge rate increased but the 14CO2 ratio to the total changed from 30% to 13%. The local radiological impact is estimated to be 1.5 μSv a-1 for Paks, 1.7 μSv a-1 for Bohunice, and 0.12 μSv a-1 for Krsko. The 14C excess in the environment has been measured at Paks NPP since 1989. Based on the monitoring data, the long-term average 14C excess from the Paks NPP was D14C=50% for hydrocarbons. Tree-ring analysis has shown a slight excess around Krsko NPP: D14C is equal to 199.9% for a tree at 1 km from the NPP compared with a “reference” one for which D14C was equal to 111.6% (in 1994).

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