Impact of atmospheric 14C to the karst environment

Naturally cosmic-ray produced radiocarbon 14C is a part of the CO2 cycle and through the atmosphere-biosphere-hydrosphere exchange process it has been introduced to the environment. Anthropogenic disturbance of the natural 14C activity caused by nuclear tests, nuclear power plants and also by fossil fuel combustion has been recorded in the atmospheric CO2. The karst environment including water, carbonate sediment and soil, where exchange processes within the CO2-HCO3 -CaCO3 system play an important role, is very sensitive to any change in the atmosphere and response to the contamination is very fast. 14C activity of atmospheric CO2 has been continuously measured in monthly samples in Zagreb area since 1983. Seasonal variations have been observed, as well as steady decrease of yearly mean values. Influence of fossil fuel combustion in the city area during winter months was also observed. Few examples of isotopic study in karst environment in Croatia and Slovenia will be presented: 1) The influence of atmospheric 14C activity to the recent carbonate precipitated in the surface water in form of tufa in the Plitvice Lakes, Korana, Krka and Zrmanja rivers in Croatia, and Krka river in Slovenia; 2) 14C activity in recent speleothems from several caves in Croatia and Postojna Cave in Slovenia; 3) Distribution of 14C activity in the surface soil in Plitvice Lakes and Postojna areas; 4) 14C activity of atmospheric CO2 inside and outside the Postojna Cave, 5) 14C activity in recent plants (aquatic and terrestrial) and shells. The stable isotopes δ 13C and δ 18O for some of the samples above will be presented too. Distribution of 14C in the karst environment will be discussed and compared with 14C activity of atmospheric CO2