Evidence for an aquatic plant origin of ketones found in Taihu Lake sediments

Abstract

This is the first time that aquatic plants have been singled out as the major source of alkan-2-ones in the sediments of a freshwater lake. Formerly alkan-2-ones were regarded as products of microbiological oxidation of corresponding alkanes or β-oxidation and decarboxylation of fatty acids. The presence of alkan-2-ones in both the cyanobacteria, high aquatic plants and sediments of Taihu Lake in the eastern China is viewed as evidence for the biogenic origin of these compounds. Taihu Lake is one of the largest freshwater lakes in China. The dominant species in the West Taihu Basin is blue-green algae; the East Taihu Basin is covered by vascular plants. We have analyzed the ketones and saturated hydrocarbons in the surficial sediments and in plant samples from Taihu Lake. We found that the distribution models of alkan-2-ones in the sediment samples from Taihu Lake were very similar to those that we found in the aquatic plants from the lake's western and eastern basins. The western basin interrelation coefficient was 0.91 and the Eastern Basin interrelation coefficients were 0.80 and 0.75 for emergent plants and submergent plants, respectively. These are shown as the similar major carbon peaks, L/H, OEP and high abundance of 6,10,14-trimethylpentadecan-2-one etc. But there are poor relationships between the alkan-2-ones in the sediment with corresponding the normal alkanes in the sediment of West Taihu Basin (interrelation coefficient is 0.68) and in the East Taihu Basin (interrelation coefficient is 0.41). The alkan-2-ones of the surficial sediment in the West Taihu Basin are from blue-green algae and in the East Taihu basin are from vascular plants. The different distributions of sediment alkan-2-ones in the two basins are possible to be used as an indicator of algae-type and macrophyte-type lakes.