Characterization of n-alkanes and their carbon isotopic composition in sediments from a small catchment of the Dianchi watershed

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 C-15-C-33 with a strong predominance of odd-numbered n-alkanes, maximizing at n-C-27, n-C-29 and n-C-31. Organic carbon to nitrogen (OC/N) ratio indicates a strong terrestrial influence on the OM. The values of delta C-13(27), delta C-13(29) and delta C-13(31) of n-alkanes range from -36.1 parts per thousand to -26.1 parts per thousand, -34.1 parts per thousand to -30.1 parts per thousand and -33.8 parts per thousand to -28.7 parts per thousand, respectively, suggesting a mainly C-3 land plants origin. The carbon preference index (CPI25-31), odd-even preference (OEP27-31), average chain length (ACL(25-33)), pristine/phytane (pr/ph), Paq, (C-27 + C-29)/2C(31), nC(16-23)/nC(24-33) and 3C(17)/(C-21 + C-23 + C-25) values are also consistent with the predominance of C-3 land plant-derived OM. Different sources of OM are reflected by the peak of n-C-15, 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. (C) 2014 Elsevier Ltd. All rights reserved.