Effect of Temporary Loading of Nonylphenol on a Summer Planktonic Community in a Eutrophic Pond

Recent studies reveal one of the representative endocrine disrupters of nonylphenol affects on the composition of a planktonic community. Since nonylphenol is sometimes discharged into eutrophic waters, we monitored planktonic community composition of a eutrophic pond after receiving nonylphenol when cyanobacterium Microcystis aeruginosa mainly dominated. The experiment was carried out two times using small-scale microcosms in a laboratory. In both two experiments, ciliate abundances significantly decreased when nonylphenol was added. On the seventh day, the ciliate abundances in $10{\mu}g\;L^{-1}$ added treatments decreased by 36.9% in the first experiment and 33.6% in the second, when compared to the control. The response of other planktonic groups was less obvious to nonylphenol addition. In particular, in the first experiment, Chl. b/Chl. $\alpha$ and Chl. c/Chl. $\alpha$ significantly increased with the addition of nonylphenol, while total Chl. $\alpha$ concentration did not change. Indeed, bacillariophyceae and chlorophyceae abundances tended to increase with nonylphenol dosing. From these results, we tentatively hypothesized that nonylphenolloading positively affects on abundances of edible phytoplankton such as Scenedesmus spp. and diatoms by releasing from grazing pressure due to decrease in ciliate abundances. The present study emphasizes that the indirect effect of endocrine disrupters should be paid more attention when freshwater resources are polluted by them.