TERRAPUB Geochemical Journal

Geochemical Journal, Vol. 53, 2019

Hydrogen isotopic composition of n-alkanes in sediments from freshwater Fuxian Lake in subtropical, China: Implications for the ecological environment


1Key Laboratory of Petroleum Resources, Gansu Province/Key Laboratory of Petroleum Resources Research, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China
2School of Earth Science & Resources, Chang'an University, Xi'an 710054, China
3Shaanxi Center of Mineral Geological Survey, Xi'an 710068, China
4Exploration and Development Institute of Changqing Oilfield Company, CNPC, Xi'an 710021, China
5China University of Mining and Technology, Xuzhou 221116, China
6Research Institute of Petroleum Exploration and Development, Lanzhou 730020, China
7Earthquake Research Institute of Lanzhou, SSB, Lanzhou 730000, China

(Received June 20, 2018; Accepted January 31, 2019)

Abstract: The normal alkanes (n-alkanes) and their hydrogen isotopic (δD) values in sediments and aquatic and terrestrial plants from Fuxian Lake area of China were analyzed by gas chromatography-mass spectrometry (GC-MS) and GC-isotope ratio mass spectrometry (GC-IRMS), respectively. According to the δD values of the odd carbon-numbered n-alkanes, the sediment samples were divided into types I and II. The type I samples had a heavier hydrogen isotopic composition (-161 to -155‰ on average) compared to that of the type II samples (-208 to -173‰ on average). This isotopic difference is likely a result of their different biological sources. Similarity in the average n-alkane δD values in the sediments and plants indicated that C17 and C21 to C25 were mainly derived from aquatic submerged plants in the lake, C27 and C29 mainly from woody plants from the surrounding area, and C31 and C33 principally from a mixture of terrestrial herbaceous and woody plants. The results further demonstrate that n-alkane hydrogen isotopic composition can be used as an useful source indicator. The study also suggests that the ecological environment of the lake area is an important factor controlling the hydrogen isotopic composition of lake sedimentary n-alkanes. This study also found that the plots of the sedimentary n-alkane δD values and the average n-alkane chain length (ACL values), and the sedimentary n-alkane δD values and relative contribution of n-alkanes from woody and terrestrial herbaceous plants (Qw values) can distinguish sediment samples from the two different ecological environments of Fuxian Lake and Gahai Lake. Our results also show that the effect of the ecological environment on hydrogen isotopic composition of sedimentary n-alkanes should be considered when reconstructing paleoclimatic and hydrologic conditions using sedimentary n-alkane δD values.
Key words: Fuxian Lake; Freshwater lake sediment; n-Alkane; Hydrogen isotope; Biological source

*Corresponding author E-mail: duany@lzb.ac.cn