CARBON UPTAKE IN AQUATIC PLANTS DEDUCED FROM THEIR NATURAL C-13 AND C-14 CONTENT

delta-C-13 and C-14 activity measurements were made on terrestrial, marsh and aquatic plants growing in their natural habitat of the Plitvice Lakes in northwest Yugoslavia. delta-C-13 values were ca -47 parts per thousand for aquatic mosses, which indicate that the carbon source was dissolved inorganic carbon (DIC) from alkaline karst waters, following a C3 pathway, and ca -25 parts per thousand for marsh plants, indicating the carbon source was atmospheric CO2. C-14 activity of true aquatic plants and submerged parts of helophytes was close to C-14 activity of DIC, whereas that of emergent parts of helophytes and terrestrial plants was similar to atmospheric CO2 activity. Aquatic plants which use DIC in freshwater for their photosynthesis are not suitable for C-14 dating, unless the initial activity of incorporated carbon is known. delta-C-13 values of plant material also depend on the carbon source and cannot be used for C-14 age correction.