Determination of sedimentation rates and life of Kodaikanal Lake, South India, using radiometric dating (210Pb and 137Cs) techniques

Abstract

A study describes the use of natural ( 210 Pb) and anthropogenic ( 137 Cs) radiometric dating techniques to determine sedimentation rates and life of Kodaikanal Lake. The core sediment from 46 cm was collected and analyzed for 210 Pb and 137 Cs using an Alpha spectrometer 7200-04 and a Gamma-ray spectrometer GC-3520.Bathymetry studies aided in the selection of a representative sample location and the measurement of the lake's underwater depth, with maximum and mean depths of 11 and 3.38 m, respectively. The maximum and minimum dry bulk density ranged from 0.57 to 1.05 g/cm 3 (mean of 0.73 g/cm 3 ), and the weight percentage of porosity collected sediment sample ranged from 60.33 to 78.63 wt. % (mean of 72.32 wt. % ). This study determined the sediment grain size as well as the percentages of sand, silt, and clay. The findings indicate that the core sediment samples contain 56.05 to 69.62 wt.% (mean of 63.21 wt.%) sand, 28.03 to 41.71 wt.% (mean of 34.55 wt.%) silt, and 1.81 to 3.98 wt.% (mean of 2.34 wt.%) clay. For geochronology studies in core sediments, the 210 Pb technique was used to assess a model of time changes in the deposit. The sedimentation rate depended on the consistent rate supply (CRS) of the 210 Pb model. The 210 Pb model was confirmed using 137 Cs radioactivity released into the global fallout after nuclear testing (1963) and the Chernobyl accident (1986). The depth concentration of 210 Pb ranged from 3.89 ± 0.1 to 15.4 ± 1.6 Bq/kg with a mean of 210 Pb concentration is 7.23 ± 0.86 Bq/ kg. The 137 Cs radioactivity was varied from the upper and lower peaks that appeared clearly at depths of 16 and 29 cm, respectively, with successive phases of 18.68 ± 1.36 and 22.04 ± 1.4 Bq/kg. According to the CRS model, the mean sedimentation rate was 0.51 ± 0.14 cm/year, and the core age was 86 years. The 137 Cs have likely been the mean sedimentation rate of 0.535 ± 0.07 cm/year and 83 years. The evaluated life of Kodaikanal Lake as an average of 210 Pb and 137 Cs sedimentation rate since 1933 is about 650 ± 24 years and 582.75 ± 19 years.