engleski

Towards a deeper understanding how carbonate isotopes (14C, 13C, 18O) reflect environmental changes: A study with recent 210Pb-dated sediments of the Plitvice Lakes, Croatia

Five short cores (top 40 - 45 cm of sediment) from four lakes of the Plitvice Lakes system were measured for 210Pb, 137Cs, a14C, d13C, d18O to study the influence of environmental changes on the sediment system in small and large lakes. Sediment chronology based on the constant flux (CF) 210Pb model was the most reliable. Lake sediments consisted mainly of autochthonous carbonates with higher sedimentation rate in small lakes. Sediments from the two large lakes, Prošće and Kozjak, showed constant stable isotope profiles for the carbonate fraction and full agreement between the 137Cs and 210Pb chronologies. Sediments from the two small lakes, Gradinsko and Kaluđerovac, showed synchronous increases in 14C and  13C and disturbed 137Cs records. All lakes showed an increase in a14C in the carbonate sediments above the first occurrence of 137Cs which was interpreted as a damped (~10 pMC increase in a14C), and decades-delayed consequence of the bomb-induced increase in a14C in atmospheric CO2. For the small lakes, increased d13C in the last two decades and part of the a14C increase is probably due to an increase in primary productivity that enhanced biologically-induced calcite precipitation with concomitant changes in the carbon isotopic composition of carbonate sediments. d13C values of a near-shore sediment core close to the confluence of one of the tributaries of Lake Kozjak showed that the carbonates in this core are a mixture of autochthonous and eroded allochthonous mineral carbonate. This core had a higher fraction of organic material. Sedimentation rate at this core site was high, but rates could not be quantified by 210Pb, 137Cs or 14C.

Plitvice; lake sediments; 14C; 137Cs; 210Pb; 13C; primary productivity; eutrophication

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