Use of the 210Pb method in studies of the development and human-impact history of some Estonian lakes

Sediment cores from six lakes of Kurtna Lake District (northeast Estonia) were investigated using 210Pb and loss-on-ignition techniques. Most of the cores were also analysed for microelement concentrations. These investigations show that since the early 1950s, when the processing of oil-shale in the study area began, the emission of fly ash to the atmosphere rapidly increased; moreover, some lakes have received waste water from mining operations. In all the cores, element concentrations have increased and organic matter content decreased. The depth at which these changes began in each core can be used as a reference level to check the reliability of the 210Pb dates. Disagreement between the 210Pb dates and the documented history of human impact is apparent in most cases and possible explanations are discussed.