Response of laboratory ecosystems to environmental stress: Effect of phenol

Ecologically realistic laboratory and field simulated ecosystems (microcosms and mesocosms) are playing increasing roles in fate and effect testing of chemicals and mixtures. Controlled ecosystems allow evaluation of toxicant effects on collective and emergent ecosystem properties. Information is needed to evaluate the validity of test system responses, interpretability of results, and cost effectiveness of simulated ecosystem tests. We developed replicate microcosms using periphyton on polyurethane artificial substrates. Source communities were obtained from two ecosystems—a reservoir in Kentucky and a softwater pond in Virginia—and tested for effects of continuous inputs of phenol (up to 30 mg/L) over 21 days. System responses measured included several biomass estimators, net oxygen production, and protozoan species richness. Communities were generally insensitive to phenol input. Primary production in microcosms from both ecosystems was inhibited at phenol concentrations >10 mg/L and chlorophyll a concentrations were also depressed. Other biomass estimators (protein, hexosamine) were not affected or were stimulated at lower (⩽10 mg/L) phenol concentrations. Protozoan species numbers were not affected. Functional shifts in the communities preceded adverse structural effects. Effect levels were similar for both communities, although the more complex community with greater biomass (Kentucky) showed more significant responses than the simpler community (Virginia). Systems showed resistance to phenol levels that were actually toxic in standard single-species tests, suggesting that ecosystems may differ in magnitude and rate of response to some nonpersistent toxicants.