ABSTRACT
This chapter addresses the use of field studies to assess the potential effects of chemicals on aquatic organisms. It presents an overview of the experimental design, procedures, and advantages and disadvantages of different “outdoor” aquatic field studies. The multitude of environmental factors, the dynamic aspects of short- and long-term biological cycles, and the critical importance of organism interactions in determining the response of ecosystems to a stressor can create considerable uncertainty in the degree to which results of single-species tests can be extrapolated to field situations. An important reason for conducting large-scale, field-type, multispecies tests is to investigate higher-order structural and functional properties of ecosystems. Multispecies toxicity tests such as mesocosms or microcosms are simplifications or models of natural ecosystem behavior and are intermediates between the entire field ecosystem and single-species toxicity tests conducted under laboratory conditions. Field studies can be an important component for evaluating and understanding the biological and ecological effects of chemicals under natural conditions.
