Isotopic Tracing of Trophication Processes over the Last Millennia on Lake Chenghai

Multi-parameter studies (stable isotopes in carbonate and or ganic matter, pigment, organic carbon and nitrogen contents) from a 660-yr cont inuous sediment core from Lake Chenghai, a closed, eutropic lake in southern Chi na, provide information on lake historical eutrophication. During the last 660 y ears, great changes have taken place in productivity and eutrophication of Lake Chenghai in response to human activities. In 1690, the productivity of the lake began to increase as Lake Chenghai became closed from agriculture in the lake’s watershed. In 1942, Lake Chenghai evolved to eutrophic state, marked by an incr ease in organic carbon, nitrogen, CaCO\-3, pigment contents and obvious negative values of stable isotopes, which is more or less simultaneous with the large-s cale population immigration during the period. In 1984, intensive human activiti es induced modern lacustrine productivity and eutrophic level. Human-induced tr ophic changes during the past few decades have affected the Lake Chenghai ecosys tem to such an extent that it has never experienced before in the last 660 years .