The sediment record is repeatedly interrupted by so-called turbidites that consist of stiff clay.
The clay horizons display a drop in unsupported 210Pb and 137Cs and a higher signal of supported 210Pb than the non-clay horizons.
In the reconstruction of the sedimentation history during the pre-industrial and industrial periods, which usually spans the past 100 years, the natural occurring radionuclide 210Pb and the artificial radionuclides 137Cs and 241Am are widely applied tracers.
137Cs is used as an independent time marker for end the atmospheric bomb test fallout in 1963 and the Chernobyl accident in 1986.
As the 137Cs signal is often weakened due to its mobility in sediments, 241Am, less mobile than 137Cs and derived from decay the bomb fallout of 241Pu, is used as a second time marker of the 1963 event.
Correct dating of those sediments is a prerequisite for chronological reconstruction of the flux of pollutants and organic matter from the water column to the sediments and hence, the reconstruction of the pollution and eutrophication events.The efficiency and self-absorption curves are obtained for specific radionuclide and standards. A 70-cm long 5-cm internal-diameter wide core was used for sediment sampling.Each core was sectioned into 3 cm intervals from the top (an estimated value, determined Ra contents were separated by the method described in Moreira’s studies .It is the so-called Constant Initial Concentration (CIC) model. There is another model for calculating this flux and the sedimentation rate is the Constant Rate of Supply model (CRS), which assumes a constant unsupported lead-210 flux to the sediment, but permits the sediment supply to vary [4,5,6].According to this model (Figure 1): Bi ingrowth) and then counted in a gas flow proportional detector.