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

Multi-parameter studies (stable isotopes in carbonate and organic matter, pigment, organic carbon and nitrogen contents) from a 660-yr continuous sediment core from Lake Chenghai, a closed, eutropic lake in southern China, provide information on lake historical eutrophication. During the last 660 years, 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 increase in organic carbon, nitrogen, CaCO[sub3], pigment contents and obvious negative values of stable isotopes, which is more or less simultaneous with the large-scale population immigration during the period. In 1984, intensive human activities induced modern lacustrine productivity and eutrophic level. Human-induced trophic changes during the past few decades have affected the Lake Chenghai ecosystem to such an extent that it has never experienced before in the last 660 years. [ABSTRACT FROM AUTHOR]