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

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 (210)Pb(ex) and (137)Cs dating. delta (13)C(inorg), delta (18)O(inorg) and delta (13)C(org) values and concentrations of C(inorg), C(org), N and P within the sediment cores have been measured. C(org) has an average deposition flux of 12.7 g/m(2) and an accumulation flux of 7.20 g/m(2). The calculated decomposition rate constant is 0.017 a(-1) with a half life of 40 a. delta (13)C(inorg) and delta (18)O(inorg) values range from - 1.6 to - 7.9parts per thousand and - 5.7 to - 13.6parts per thousand, 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. delta (13)C(org) ranges from - 25 to - 28parts per thousand, indicating that the organic matter originated mainly from land-derived plants, with overprinting from anthropogenic activities over the past 460 years (since 1537 AD), N and P g concentrations show a similar vertical distribution to C(org). 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. (C) 2002 Elsevier Science Ltd. All rights reserved.