Effects of linear alkylbenzene sulfonate (LAS) on the interspecific competition between Microcystis and Scenedesmus

Abstract

The widespread use of detergents increases the concentration of surfactant in lakes and reservoirs. High surfactant loads produces toxicity to algae; however, the influence of the increasing surfactant on the competition between algae is not clear. In this paper, different amounts of linear alkylbenzene sulfonate (LAS) were added to test the effects of LAS on the competition between Microcystis aeruginosa and Scenedesmus obliquus under eutrophic condition. In single culture, the growth of S. obliquus was promoted under lower LAS concentrations (1 and 20mgL(-1)), but cell density of S. obliquus reduced when treated with higher LAS concentration (100mgL(-1)). The growth of M. aeruginosa was inhibited markedly with 20 and 100mgL(-1) LAS. Compared with single culture, the result was opposite in co-cultures and the cell density of S. obliquus increased significantly when treated with LAS of 1, 20, and 100mgL(-1). The specific growth rates of S. obliquus and M. aeruginosa in both cultures were 0.4-0.5day(-1) and 0.6-0.7day(-1), respectively, except that the specific growth rate of M. aeruginosa in both cultures treated with 100mgL(-1) LAS was about 0.2day(-1). M. aeruginosa dominated over S. obliquus in the co-culture without LAS, while the competition was completely opposite with the addition of 20mgL(-1) LAS. The growth of S. obliquus treated with 20mgL(-1) LAS was not affected significantly in single culture but was promoted by 75% in co-culture. Moreover, the growth of S. obliquus in co-culture treated with 100mgL(-1) LAS was promoted by more than 97%. These results suggested that the increasing LAS would overturn the competition of algae in freshwater ecosystems.