Molecular biomarkers for sources of organic matter in lacustrine sediments in a subtropical lake in China

N-alkanes distributions and stable isotopic compositions (δ13C and δ15N) in the lacustrine sediments of Shijiu lake were measured to assess whether biological source information was recorded in the molecular biomarker. Results showed regular unimodal n-alkanes distribution in range of C16–C33 with strong predominance of odd-numbered n-alkanes, maximizing at C29. The δ15N for SON were uniformly low, ranging from −6.7‰ to 3.8‰ and C/N ratios ranged from 6.6 to 10.0, suggesting that most of organic matter was influenced by terrestrial characteristics of the watershed. The δ13C for C27 to C31n-alkanes and for SOC varied from −32.9‰ to −26.6‰ and −23.4‰ to −21.6‰, respectively, falling within the range of corresponding n-alkanes in leaves mainly from C3 land plants. The values of C/N, CPI, OEP, ACL and C27/C31 exhibit similar temporal changes with the primary production, showing enhanced eutrophication resulted from increased anthropogenic activities in Shijiu lake from 1852 to 2010.

► Unimodal odd-numbered n-alkanes distribution in range of C16–C33 were observed.
► The values of C/N, CPI, OEP, ACL and C27/C31 exhibit similar temporal changes.
► Results of δ13C showed the source of organic matter was mainly from C3 land plants.
► Anthropogenic activities enhanced eutrophication in Shijiu lake from 1852 to 2010.