Abstract
The biomarker composition and stable carbon isotope values of organic matter (OM) in sediment cores from Shuanglong catchment of the Dianchi watershed show an unimodal n-alkane distribution ranging from C15–C33 with a strong predominance of odd-numbered n-alkanes, maximizing at n-C27, n-C29 and n-C31. Organic carbon to nitrogen (OC/N) ratio indicates a strong terrestrial influence on the OM. The values of δ13C27, δ13C29 and δ13C31 of n-alkanes range from −36.1‰ to −26.1‰, −34.1‰ to −30.1‰ and −33.8‰ to −28.7‰, respectively, suggesting a mainly C3 land plants origin. The carbon preference index (CPI25–31), odd-even preference (OEP27–31), average chain length (ACL25–33), pristine/phytane (pr/ph), Paq, (C27+C29)/2C31, nC16–23/nC24–33 and 3C17/(C21+C23+C25) values are also consistent with the predominance of C3 land plant-derived OM. Different sources of OM are reflected by the peak of n-C15, ascribed to a contribution by aquatic algae and photosynthetic bacteria. Eutrophication seems to be enhanced by both autochthonous (weak) and allochthonous (strong) contributions of OM. A major factor affecting the OM accumulation in the catchment and OM transportation to the Dianchi Lake may be increased by human activities from 1871 to 2011.
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