Recent changes in Red Lake (Romania) sedimentation rate determined from depth profiles of 210Pb and 137Cs radioisotopes

This work presents a first estimation of the sedimentation rate for the Red Lake (Romania). The sediment accumulation rates were determined by two well-known methods for recent sediment dating: Pb-210 and Cs-137 methods. Both techniques implied used the gamma emission of the above-mentioned radionuclides. The Pb-210 and Cs-137 concentrations in the sediment were measured using a gamma spectrometer with a HpGe detector, Gamma-X type. Activities ranging from 41 +/- 7 to 135 +/- 34 Bq/kg were found for Pb-210 and from 3 +/- 0.5 to 1054 +/- 150 Bq/kg for Cs-137. The sediment profile indicates acceleration in sedimentation rate in the last 18 years. Thus, the sedimentation process for the Red Lake can be divided in two periods, the last 18 years, and respectively, the period before that. Using the Constant Rate of Pb-210 Supply method values between 0.18 +/- 0.04 and 1.85 +/- 0.5 g/cm(2) year (0.32 +/- 0.08 and 2.83 +/- 0.7 cm/year) were obtained. Considering both periods, an average sedimentation rate of 0.87 +/- 0.17 g/cm(2) year (1.17 cm/year) was calculated. Considering an average depth of 5.41 m for the lake and the sedimentation rate estimated for the last 18 years, it could be estimated that the lake will disappear in 195 years. (C) 2009 Elsevier Ltd. All rights reserved.