n-Alkane distributions and concentrations in algae, submerged plants and terrestrial plants from the Qinghai-Tibetan Plateau

Long chain n-alkanes (C27–C33) in lake sediment records are commonly considered to be terrestrial plant biomarkers when reconstructing paleoclimatic and paleolimnological history. However, the extent to which their accumulation is influenced by n-alkanes originating from algae and submerged plants is largely unclear. Furthermore, to our knowledge, few studies have systematically analyzed the variation in n-alkane concentration or distributions between different submerged plant and algal species. We systematically investigated the n-alkane distributions of 13 algae (including 10 Cladophora and 3 Spirogyra), 68 submerged plants (including 37 Potamogeton, 7 Myriophyllum, 4 Ruppiaceae and 20 Chara) and 13 terrestrial plants (including 7 grasses and 6 shrubs) from 16 Qinghai-Tibetan Plateau lakes. The results indicate that the total n-alkane (C21–C33) concentration varied between different submerged plants. Potamogeton, Myriophyllum and Ruppiaceae exhibited high concentration, with average values 235.8, 295.9 and 275.9μg/g, respectively. These values were slightly higher than the concentrations found in terrestrial plant leaves (avg. 206.4μg/g), whereas the average concentration in Chara was only 2.0μg/g, significantly lower than that of other submerged plants. Similarly, the concentration in algae was also very low, with average values of 2.0μg/g and 4.0μg/g for Cladophora and Spirogyra, respectively. Submerged plant and algal long chain (C27–C33) alkanes accounted for a large proportion of the total C21–C33n-alkanes, with average ratios (long chain vs. total n-alkanes) of 20, 3, 22 and 27% for Potamogeton, Myriophyllum, Ruppiaceae and Chara, respectively. Cladophora and Spirogyra exhibited average ratios of 34% and 65%, respectively. Therefore, submerged plant long chain n-alkane contributions to lacustrine sediments, especially those of Potamogeton and Ruppiaceae, should not be considered negligible due to their high n-alkane concentration. Conversely, some algae, such as Cladophora and Spirogyra, minimally contributed n-alkanes to the lake sediments.