Distributions of n-alkanes and their hydrogen isotopic composition in plants from Lake Qinghai (China) and the surrounding area

Various aquatic plants from Lake Qinghai, the largest inland saline lake in China, and terrestrial plants from the surrounding area were investigated for the distribution of n-alkanes and their delta D values. The n-alkanes in the samples range from C-15 to C-33 with C preference index (CPI) values of 4.0-29.7. The n-C-23 or n-C-25 alkane is the dominant compound in the aquatic submerged plants. The aquatic emergent and terrestrial plants have an abundance maximum at n-C-27, n-C-29 or n-C-31. The average chain length (ACL) values, ranging from 26.0 to 29.6, are closely related to the plant species. The n-alkanes from the aquatic plants have mean delta D values of -169% to -121% and those from the terrestrial plants values of -173% to -109%. The H isotopic composition (delta D) and fractionation differ significantly among the plants studied. Comparison shows that additional evaporative enrichment of the lake water associated with saline lakes and humidity influence the delta D values of the n-alkanes in aquatic and terrestrial plants, respectively. The mean delta D values of n-alkanes in the plants decrease with increasing ACL value. The n-alkanes from the different types of plants are more depleted in D relative to environmental water and those from aquatic plants (with a mean value of -143%) have a greater isotopic fractionation than terrestrial plants (mean value -113%). (C) 2011 Elsevier Ltd. All rights reserved.