HOLOCENE ENVIRONMENTAL HISTORY OF A PEATLAND IN THE LENA RIVER VALLEY, SIBERIA

A 3.86 m core of peat and organic lake mud from a polygonal peatland i n the Lena River valley of Siberia was radiocarbon dated and analyzed for pollen, plant macrofossils, chrysophyte stomatocysts, stable isoto pes, and charcoal. At around 7200 BP, a shallow lake or open-water wet land supported diverse aquatic macrophytes. The site had transformed i nitially into a richer fen with Carer, Comarum palustris, and Drepanoc ladus and later a poorer fen with Sphagnum which persisted until aroun d 3000 BP. Fire may have been responsible for silt being blown onto th e peatland, which changed the hydrological and geochemical conditions for development of the poor fen. Ice accretion led to an increase in t he height of the centre of the polygon and expansion of Sphagnum peatl and. O-18 values become progressively more enriched, which reflects mo re direct input of summer precipitation waters and less groundwater du ring this period. Finally, the peatland surface was elevated sufficien tly to limit water and nutrient supply, thereby allowing Ericaceae and Betula to grow at the coring site. Fire burned the peatland surface a nd may have exaggerated the extremely slow rate of peat accumulation F ire may also be a factor in maintaining the open Larix dahurica forest in the region today, while climate may be contributing to reducing po stfire regeneration. Fire and climate together may be controlling the character and composition of forests near tree line in the Lena River valley of this part of Siberia.