Environment changes influenced by human activities at Lake Gucheng

Abstract

Sedimentary cores were taken from the center part of Lake Gucheng, Jiangsu in 2005. The total organic carbon, total nitrogen, phosphorus, metals were analyzed. Calculations of sedimentation rates were achieved using 210Pb CRS method. The results demonstrated that average sedimentation was 0.067 cm/a after 1980s corresponding to that from Chernobyl accident marker occurred at 1986. During the period of 1920s and 1980s, the sedimentation rates varied between 0.056 and 0.167cm/a. The high sedimentation rates found in 1960s may be associated with the intense reclamation since 1960s. Cu, Pb, Zn, Cr showed up-core increase in the top 30 cm sediment. Combined with the ratio of these elements to Ti it was concluded that the origin of Cu, Pb, Zn, Cr was not wholly from natural processes. The age was between 6500-8000a BC based on AMS 14C results from depth 0.5 m to 1.78 m, which was comparable with OSL age of 7-8 ka from the same depth. Sharp transition of index including TOC, TN and metals emerged at depth of 0.3 m may indicate that sediments could be eliminated due to erosion or human impact such as cultivation. It was reported that Lake Gucheng was isolated from Lake Taihu due to establishment of Xiaba at 1556 A.D. Taken the depth of 30 cm as the time when Xiaba was established, the average sedimentation rate was calculated to be 0.067cm/a which was in agreement with the results of 210Pb and 137Cs method. Therefore, continual deposition may occur after the isolation of Lake Gucheng from Lake Taihu.