Comparison of molecular distributions and carbon and hydrogen isotope compositions of n-alkanes from aquatic plants in shallow freshwater lakes along the middle and lower reaches of the Yangtze River, China. (August 2021)

• Record Type: Journal Article
• Authors: Yu, Xiaofang; Lü, Xiaoxia; Meyers, Philip A.; Huang, Xianyu
• Is Part Of: Organic geochemistry. Volume 158(2021)
• Publication Date: 2021-08
• Subjects: n-Alkanes -- Aquatic plants -- Carbon isotope -- Hydrogen isotope -- Fractionation; Organic geochemistry -- Periodicals; Biogeochemistry -- Periodicals; Géochimie organique -- Périodiques; 553.205
• DOI: 10.1016/j.orggeochem.2021.104270
• Languages: English
• ISSNs: 0146-6380

Abstract

Highlights: n -Alkanes were investigated in aquatic plants collected from shallow lakes in the Yangtze MLYR. Combining P aq and δ 13 Calk can distinguish contributions from submersed, floating and emersed plants. εalk/water values in submersed plants of MLYR are consistent with previous studies. δ 2 Halk values of submersed plants are more negative than those of C3 dicots growing in humid monsoon climate. Abstract: Leaf wax n -alkanes in lacustrine sequences have been widely applied for reconstructions of Late Quaternary paleoclimate histories. Such applications depend on knowledge of the factors controlling the characterization of the n -alkane paleoproxies of aquatic plants. This study analyzed the molecular distributions and carbon and hydrogen isotopic compositions of n -alkanes of aquatic plant samples collected from the middle and lower reaches of the Yangtze River (MLYR). In this collection, the n -alkane distributions of submersed/floating plants and emersed plants are distinctly different. By combining their P aq and n -alkane δ 13 C values, the n -alkane contributions from submersed plants and emersed plants in the MLYR can be differentiated. It is also noteworthy that the hydrogen isotope fractionation (εalk/water ; avg. −166‰) between the n -C23 alkane of submersed plants in the MLYR and in precipitation agrees well with previous studies, suggesting a nearly constant εalk/water for the submersed plants. Moreover, compared to C3 dicots growing in a similar climate, submersed plants in the humid MLYR have lower n -alkane δ 2 H values. This feature may arise from isotopic differences in the evapotranspiration of lake water versus leaf water and in the biosynthetic fractionations of leaf waxes of these two plant groups. These results aid interpretations of the hydrogen isotope offset of the δ 2 H values of n -alkanes between aquatic and terrestrial plants in humid climates.