Spatial and seasonal variations in the stable C isotope composition of dissolved inorganic carbon and in physico-chemical water parameters in the Plitvice Lakes system.

Plitvice Lakes waters were collected at 14 sampling points, including springs, tributaries and lakes, for the period 2002-2007. The results of the physical and chemical conditions of calcite precipitation as well as the δ(13)C values of dissolved inorganic carbon (DIC) were used to study the processes influencing calcite precipitation. Significant differences between spring, lake and stream waters as well as changes in the downstream direction were observed. The correlation between δ(13)C(DIC) values and physico-chemical conditions for calcite precipitation showed that calcite precipitates in lake waters which are oversaturated with respect to CaCO(3) (I (sat) values 4-10) and with δ(13)C(DIC) values between-11.5 and-8.5 ‰. In spring waters, the δ(13)C(DIC) values were more negative, from-14 to-12 ‰, and I (sat) values of 1-2 indicated that equilibrium conditions for calcite precipitation were not attained. The downstream increase in δ(13)C(DIC) correlated with the increase in the δ(13)C values of calcite in the lake sediments, suggesting that the freshwater calcite was mainly of autochthonous origin and precipitated within the water column in isotopic equilibrium with DIC.