Since the adoption of mesocosm testing by the US EPA Office of Pesticide Programs as the final tier, the role of outdoor surrogate ecosystems continues to grow in importance in risk assessment of chemicals on aquatic communities. The ultimate goal of ordination techniques is to elucidate those biological and environmental factors that may be important in determining the structure of the communities from which they were collected. As pointed out by the authors, the acceptance of correspondence analysis for ordination of community data in this study must be considered tentative because of the low numbers of organisms and the lack of replication. A surfactant was chosen for this study for which the biological responses in laboratory and field studies were well known prior to the start of the experimental stream study. At present too few comparative ecosystem studies exist, even between mesocosms and natural lentic waters, making it difficult to extrapolate results from one system to another.