Environmental change and human activities during the 20th century reconstructed from the sediment of Xingyun Lake, Yunnan Province, China

The history of environmental changes and human activities in the catchment of Xingyun Lake, Yunnan Province, Southwest China, was investigated using an 85 cm sediment core drilled in the northwest part of the lake. The chronology of the sediment, established with the 210Pb method, represented the most recent 160 years of depositional history. A series of lipids, including n-alkanes and n-alkanols, were identified by using GC/MS. The distinct n-alkanes and n-alkanols distributions at different depths are indicators of environmental changes. The carbon preference index (CPI) of the n-alkanes ranges from 0.55 to 3.35. The average chain length (ACL) ranges from 19.2 to 25.7. The ratios of the C27/C31 and C27/(C15 + C17 + C19) are between 0.43–1.63 and 0.05–0.85, respectively. The ratio of the higher carbon components to the lower of n-alkanes (H/L) and n-alkanols changes from 0.16 to 3.18 and 0.24–7.36, respectively. These ratios, compared with the temperature record of the meteorological station in the catchment, reveal a remarkable relationship: high H/L values correspond to warm climate conditions and vice versa. Four stages were recognized according to the sediment records for the past 160 years: a cold period before the 1920s, a warm period from the 1920s to the mid-1950s, a cool period between the mid-1950s and 1970s, and a warm period after the 1980s. The proxies also reveal the organic origin of the lake sediment. Human activity led to great environment change, such as the Gehe channel dredging in 1923, denudation and excessive reclamation at the end of the 1950s, and especially the eutrophication of the lake since about the early 1990s. The lipids are a sensitive recorder of the environment changes, although the strong increase of human activities may affect the record of natural changes.