W.L, C., R. M.S, and P. S.M. “Assessment of Three Tropical Chlorophytes As Bioassay Organisms for Nitrogen and Phosphorus Enrichment in Freshwater Ecosystems”. Malaysian Journal of Science, vol. 26, no. 2, Aug. 2007, pp. 15-25, http://mjs.um.edu.my/index.php/MJS/article/view/8050.