Geochemical records in recent sediments of Lake Erhai: implications for environmental changes in a low latitude–high altitude lake in southwest China

Abstract

Sediment cores were collected from Lake Erhai, which is located on the Yunnan–Guizhou Plateau, a landform formed by the uplift of the Himalayas. These sediments were deposited up to about 697±15 years ago based on 210Pbex and 137Cs dating. d13Cinorg, d18Oinorg and d13Corg values and concentrations of Cinorg, Corg, N and P within the sediment cores have been measured. Corg has an average deposition flux of 12.7 g/m2, and an accumulation flux of 7.20 g/m2. The calculated decomposition rate constant is 0.017 a-1 with a half life of 40 a. d13Cinorg and d18Oinorg values range from -1.6 to -7.9‰ and -5.7 to -13.6‰, respectively, and show similar trends over the past 700 years, which is interpreted to be controlled mainly by temperature, corresponding to climatic changes of two and half periods of a ‘warm–cold–warm’ cycle. d13Corg ranges from -25 to -28‰, indicating that the organic matter originated mainly from land-derived plants, with overprinting from anthropogenic activities over the past 460 years (since 1537 Image ). N and Porg concentrations show a similar vertical distribution to Corg. Atomic ratios of organic carbon and nitrogen (C/N) are 5.8 and 6.8 for the deposition and accumulation stages, respectively, similar to the Redfield ratio in the ocean. The C/P ratio, however, is higher than that in the ocean. The vertical distribution of carbon in the sediment cores indicates that Lake Erhai has the characteristics of both an inland lake (land-derived organic matter) and the ocean (similar C/N ratio). The lower C/N and C/P ratios in the lake Erhai sediments are characteristic for a lake at high altitude and in a subtropical region. This ‘low latitude–high altitude effect’ is probably related to the uplift of the Himalayas