Anthropogenic impact on Lake Liinjärv (Rõuge, southern Estonia) was studied back to the mid-19th century on the basis of heavy metals (Pb, Cu, Zn, Mn, and Hg) and geochemical parameters of a short sediment core dated by 210 Pb isotopes. The development of the lake and its sediment composition are heavily influenced by the inflow of saturated calcareous waters that cause precipitation of calcium carbonates. The concentrations of most of the metals started to increase at the end of the 1970s. This is most clearly observable for Zn, Cu, and Pb. At the same time the distribution pattern of Mn seems to be controlled mainly by the redox conditions in the hypolimneon. The main sources of pollutants in Lake Liinjärv, due to its large catchment area, are the influence of agricultural activity and atmospheric input. Organic matter is the main factor affecting heavy metal (Pb, Hg, Cu, and Zn) distribution in lake sediments.
Sediment cores from six lakes of Kurtna Lake District (northeast Estonia) were investigated using 210 Pb 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 210 Pb dates. Disagreement between the 210 Pb dates and the documented history of human impact is apparent in most cases and possible explanations are discussed.
A comprehensive geochemical and palaeobotanical study of the lacustrine sediments of Lake Nôm mejärv from industrialized NE Estonia establishes the links between the nature and intensity of human activities and their impacts on the state and structure of the lake ecosystem. In cores of sediment formed during the last century, five zones can be distinguished, each reflecting a pattern of human activity and characterized by a particular diatom community and sediment composition. Using reliable geochronological data it is possible to compare these zones with the known industrial load on the lake and its catchment area. The information obtained is of practical value for planning the rehabilitation of this severely impacted lake.
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