C/N ratio and fossil pigments in sediments of some Estonian lakes: An evidence of human impact and Holocene environmental change

The content of carbon (C), nitrogen (N), fossil carotenoids (TC) and chlorophyll derivatives (CD) in the sediments of five Estonian lakes was analysed. Historical records of man-induced changes on catchments were used for the interpretation of the obtained data. On the basis of the C/N ratios it was estimated that the planktonic matter formed ca. 25% (C/N ratio 24) to 90% (C/N ratio 8) of the organic pool matter of lake sediments. In eutrophic Lake Ruusmae the fraction of the phytoplankton produced in lakes was highest, amounting to approximately 80-95% of the deposited organic matter. Remarkable C/N changes were noted in the sediments from lakes Matsimae and Viitna, where the content of planktonic matter has increased during last decades, reflecting an increase in recreational activity around these lakes. The variations in pigment concentrations in the sediments of lakes Matsimae and Ruusmae could be explained by changes in the land-use that have altered the intensity of primary production and conditions of TC and CD degradation before the final burial.