Concentration and distributions of fatty acids in algae, submerged plants and terrestrial plants from the northeastern Tibetan Plateau

Abstract

We systematically investigated the concentration and distributions of saturated fatty acids (FAs) in 66 submerged plants (including 48 Potamogeton, 7 Myriophyllum and 11 Ruppia), 59 algae (including 26 Chara, 20 Cladophora and 13 Spirogyra) and 32 terrigenous plants from 18 lakes on the northeastern Tibetan Plateau. The results indicate that C14-C32 FAs in algae, submerged plants and terrigenous plants were dominated mainly by C16 and C20-C32. FAs in algae and submerged plants were predominantly C24, but also contained a relatively high abundance of C26. The submerged plants had high C26-C32 concentration, with average values of 216μg/g for Potamogeton, 52μg/g for Myriophyllum and 134μg/g for Ruppia, close to those of terrigenous plants (avg. 161μg/g). Algae exhibited low C26-C32 FA concentration, with mean values of 7μg/g for Chara, 8μg/g for Cladophora and 18μg/g for Spirogyra. The C26-C32 FAs in algae and submerged plants accounted for a large proportion of C20-C32, yielding average ratios (C26-C32 vs. C20-C32) of 33, 35, 31, 15, 19 and 23% for Potamogeton, Myriophyllum, Ruppia, Chara, Cladophora and Spirogyra, respectively. Therefore, the contribution of submerged plant C26-C32 FAs to lake sediments should be considered due to their high concentration, whereas the influence of algae was minor. Meanwhile, by comparing the values of average chain length (ACL), alga/terrigenous ratio (ATR) and submerged/terrestrial ratio (STR), we found that ACL14-32 and ATR could be used to distinguish algal FAs from those of other plants and that STR could be used to differentiate FA sources from submerged and terrestrial plants. Thus, we suggest that using specific chain lengths to determine source inputs is not adequate when applying sedimentary FAs for paleoclimatic reconstruction, while ACL 14-32, ATR and STR may aid in determining FA sources in sedimentary records.