Sedimentation Rate in Bera Lake

Abstract

The evolutionary environmental history of Bera Lake was studied using the fallout radioisotopes137Cs and 210Pb. 317Cs horizons in the all ten studied cores showed a constant rate of 210Pb supply along all distinctive layers in each core. The lithology of layers significantly affected the variation of 210Pb value with depth. The chronology of Bera Lake sediment was conducted using the Constant Rate of Supply (CRS) model. The 1963 fallout maximum 137Cs from atmospheric testing of nuclear weapons found in all selected master cores at the depth of 40 cm. The mean pre-1950 sediment accumulation rate was ranged between 0.06 ± 0.02 and 0.16 ± 0.2 g cm−2 year−1. Environmental impacts of five deforestation projects performed from 1972 to 1995 at the catchment area, contributed significantly toward increasing the sedimentation rate within Bera Lake. Besides the 137Cs horizons, the charcoal horizon at the lower contact of white sandy mud revealed the datum of maximum deforestation in the study area. 210Pb dates using the CRS model correlated historical sediment fluxes to anthropogenic changes in Bera Lake catchment area. Organic-rich sediments deposited mostly at the top of the Bera Lake sediment columns with a mean rate of 0.2 ± 0.1 g cm−2 year−1 since 1994. High biomass productivity of mature oil palm plantations, which were developed in the catchment area, dictated organic-rich deposit distribution. This study highlighted capability of radioisotopes to reconstruct long-term (100–150 years) history of a natural lake at a tropical area where surrounding catchment has extensively deforested over the recent decades.