This paper describes a method for determining safe levels of chemical exposure in shallow-water communities, using laboratory microcosms as test subjects. The safe level is considered to be the maximum exposure that causes no persistent, ecologically significant changes in the ecosystem. Shallow freshwater communities in ponds, lakes, and rivers are good experimental subjects for research on contaminants, and environmental toxicologists have measured their responses to a variety of chemicals. Certain patterns of community effects have been observed, including a decline in net primary production or the production: respiration ratio, concomitant changes in water chemistry, and changes in community composition brought about by interactions among sensitive and resistant populations. The same patterns can be reproduced in microcosms containing natural sediment, water, and communities of submersed aquatic plants (macrophytes). In experiments completed at Oak Ridge National Laboratory, microcosm-derived estimates of safe exposure levels were confirmed using outdoor artificial ponds, suggesting that the microcosm procedure can be an efficient and economical means of determining safe levels for shallow-water communities.

Details of microcosm construction, techniques for monitoring ecological variables in microcosms, and an experimental design for determining safe exposure levels are provided here. The microcosms are assembled by transferring components of natural ecosystems to 80-L aquaria in a controlled laboratory environment. The communities that develop in these systems are typically dominated by common, cosmopolitan littoral species of macrophytes, algae, and invertebrates. Methods are described for measuring changes in water chemistry, phytoplankton, periphyton, macrophytes, zooplankton, and ecosystem production and respiration. By monitoring these variables over a gradient of pollutant exposure levels, the safe level can be determined accurately and precisely.