Design and construction of model stream ecosystems

A series of 12 outdoor model stream mesocosms was designed to evaluate the effects of chemicals and mixtures on the biota in stream ecosystems. An integrated design plan incorporated physical, chemical, and biological factors as well as the specific experimental objectives and effects parameters to be evaluated. Analysis of biological assemblages such as macroinvertebrates and periphyton in the model stream mesocosms demonstrated the presence of diverse and sensitive taxa. These model stream mesocosms also included the ability to evaluate responses of sentinel fish species such as Pimephales promelas and Lepomis macrochirus as well as macrophytes. The design and construction of the stream are discussed in detail and a brief description of a typical experimental protocol is provided. Experiments, to date, have spanned 14-30 days pretreatment "colonization" with 30 days of treatment and 15 days of posttreatment observation. Precision and accuracy of test chemical delivery to the stream have been excellent and the overall experimental design has been useful for delivering threshold toxicity concentrations and evaluating ecosystem potency for the chemicals tested.