Estimating Eutrophic Potential of Pollutants

Laboratory microcosms comprising approximately 7 l of lake water and 1 l of bottom mud with a species invasion pressure maintained by periodic addition of small quantities of fresh lake water were shown to retain the natural algal population diversity of the lake. The microcosms were employed to estimate both the algal growth stimulating capacity and the influence on the planktonic population characteristics of the addition of various chemicals and wastewaters. Two microcosms were maintained as controls and 16 others, in duplicate pairs, received various concentrations of a commercial fertilizer, primary effluent, secondary effluent, and algicide over a 20-week period. The best parameter for assessing the ecological significance of the various chemicals and wastewaters was found to be Shannon's diversity index. The control microcosms usually maintained a diversity index greater than 0.9. In all case, enrichment caused a decrease in the diversity of the planktonic algae.