Microcosms as Test Systems for the Ecological Effects of Toxic Substances: An Appraisal with Cadmium

摘要

A two-phase set of experiments was conducted to address some of the problems inherent in ecological screening of toxic substances in aquatic microcosms. Phase I was a 4 x 4 factorial experiment (four levels of cadmium versus four levels of nutrient enrichment) on the interactive effects of cadmium and nutrients using static microcosms. Phase II was a 2 x 4 factorial experiment (continuous and pulsed cadmium inputs versus phosphorus limited and non-limited inputs) using flowthrough microcosms to study temporal aspects of system behavior in response to nutrient limitation and chronic versus acute cadmium perturbations. Generally, as cadmium concentration increased, parameters changed to indicate more system stress, except that high nutrient levels reduced somewhat the stress effect of cadmium. Of the variables measured, community metabolism, community composition by trophic groups, and output/input ratios for NO3-N, MN and Fe provided the best indicators of system response to cadmium. Nutrient enrichment and phosphorus limitation significantly influenced cadmium effects on most of the variables studied. Pulsed cadmium early in succession significantly affected system response to cadmium pulses later in succession. A bibliography of microcosm literature is included.