[Record of ecosystem evolvement processes provided by delta 13C(org) and 6 delta 15N values in Chaohu Lake sediments]

Variations of delta 13C(org) and delta 15N values, C/N ratios, TOC and TN contents in Chaohu Lake sediments reflect the sources of organic matter in lake sediments, evolution of lake productivity and the eutrophic status in Chaohu Lake during last 100 years. Our results suggest that the sedimentary organic matter was derived mainly from aquatic algae and partly from land matter. However, the input of the pollutants from city and agriculture into the lake could not be neglected. Two stages can be found in the sediments cores according to the profiles of delta 13C(org), delta 15N values, TOC and TN contents. Below 10cm, delta 13C(org) values vary between - 21.74 per thousand and - 19.34 per thousand. Nitrogen fixing and non-nitrogen fixing phytoplankton coexist together. Two cores show different nutrition processes. Above 10cm, in both profiles, the values of delta 13C(org) start to decrease sharply, but delta 15N, TOC and TN increase. The construction of Chaohu Gate leads to the enhancement of lake productivity and development of eutrophication.