engleski

CARBON ISOTOPE (14C AND 13C) EXCHANGE PROCESSES IN THE BIOSPHERE: CASE StUDY OF THE PLITVICE LAKES

Radiocarbon activity (a14C) and ratio of stable isotopes 13C/12C (d13C values) were measured in different samples collected in the natural habitat of the Plitvice Lakes: terrestrial plants (deciduous and coniferous), marsh and aquatic plants and surface soil. The a14C and d13C values were compared with those of the atmospheric CO2 as well as of dissolved inorganic carbon (DIC) of Plitvice waters with the aim of determining origin of carbon in the biosphere. 14C activity of terrestrial plants (100 to 110 percent of modern carbon, pMC) followed 14C activity of the atmospheric CO2, with some differences between deciduous and coniferous trees. 14C activity of marsh plants partly submerged in the water (sedge) also followed the 14C activity of the atmospheric CO2. Aquatic plants completely submerged in the lake waters showed different 14C activity depending on the sampling location and their a14C correlated with the a14C of DIC. Steady increase of a14C of DIC in downstream direction was also reflected in the increase of a14C of the aquatic plants but the values were about 10 pMC higher than those of DIC. Top 20 cm of surface soil represented the average of organic material (humus) deposited in several years and a14C was slightly higher than that of atmospheric CO2 in the last year. d13C values of measured samples correlated with the origin of carbon in different materials. For the plants which used atmospheric CO2 for photosyntesis, terrestrial plants and sedge, d13C values ranged from -31%o to -27 ‰. For aquatic plants d13C values varied in wide range from -48 ‰ to -30 ‰, showing that the source of carbon was mainly DIC in water but also carbon of organic decomposition. Plants partly consuming CO2 from atmosphere and partly from DIC, e.g. moss from the waterfalls, have less negative d13C values and higher 14C activity than the aquatic plants. 14C activity and d13C values of different plants collected in the Plitvice Lakes area and their correlation with atmospheric CO2 and DIC showed which processes and/or sources of carbon were involved in formation of carbon isotope composition of the biosphere of the karst area.

14C; 13C; Plitvice Lakes; biosphere; exchange processes

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