Carbon isotope fractionation in karst aquatic mosses.

Radiocarbon activity (a14C) and 13C composition (δ13C) were measured in hygrophyte and mesophyte (land) mosses collected in the natural habitat of the Plitvice Lakes and along the Zrmanja and Krupa Rivers (typical continental and Mediterranean climates, respectively), Croatia. a14C and δ13C values of mosses, of atmospheric CO2 and dissolved inorganic carbon (DIC) were compared with contemporary data and with data from 30 years ago at the Plitvice Lakes when 14C activity of atmospheric CO2 was ∼30% higher. A positive correlation between a14Cmoss and δ13Cmoss was observed for all data reflecting the change of carbon isotopic composition in DIC along the water flows and in atmospheric CO2 regardless of the climatic regions and historic period. Fraction of the atmospheric carbon in moss (ω atm. C ) and carbon fractionation factor from aquatic CO2 (DIC) to moss tissue (ε moss / g − aq ) were calculated for each individual moss. Three species of mosses had ωatm.C ∼ 0 % implying that they turn to anabiosis during dry periods. The relation ε moss / g − aq vs. ω atm. C differentiates true aquatic and amphiphyte mosses. The first had a statistically significant negative correlation between ε moss / g − aq and ω atm. C . The amphiphyte mosses had lower ε moss / g − aq with higher water flow rates. [ABSTRACT FROM AUTHOR]