C, N STABLE ISOTOPE RECORDS OF ENVIRONMENTAL CHANGES IN BOSTEN LAKE DURING THE PAST 200 YEARS

Two sediment cores were recovered from the Bosten Lake in order to investigate the changes in both the lake system and source of organic materials during the last 200 years.Based on ²¹⁰Pb/¹³⁷Cs chronology, stable isotopes of organic carbon and nitrogen as well as Loss on Ignition (LOI), grain size and magnetic susceptibility (MS) were analyzed.The results indicate that the agricultural activities in the catchment of the Bosten Lake have much earlier influence in the lake center rather than in the river mouth.Due to the general increase in regional humidity during 1810-1883 AD, δ¹³C_org declined rapidly in the core BST16, while abrupt increases in δ¹⁵N were found as more terrestrial material could reach the lake center.After the establishment of Xinjiang Province in 1884 AD, intensified agricultural activities have led to marked decrease in the medium grain size, and relatively higher δ¹³C_org and lower δ¹⁵N in the core BST16.Since 1950 AD, large scale agricultural activities have led to the rapid decrease in δ¹³C_org and increase in δ¹⁵N, indicating a general increase in the trophic level.Further decrease in δ¹⁵N together with the increasing δ¹³C_org after the 1990's indicates that nitrogen fixation by algae began to dominate the lake primary productivities.