A research strategy for using stream microcosms in ecotoxicology: Integrating experiments at different levels of biological organization with field data

Environmental pollutants and other stressors can haveeffects at many different levels of biologicalorganization and a key step in the design ofecotoxicological studies is the formulation ofhypotheses that explicitly state the level(s) ofbiological organization that the study is meant toaddress. For example, single species studies at theindividual organism level can provide key informationon individual growth rates and physiologicalresponses, while multispecies studies at the communitylevel allow food web investigations to be undertakenand potentially allow indirect effects of toxicants tobe identified. The integration and understanding ofprocesses operating over several different levels ofbiological organization can often be greatlyfacilitated by the incorporation of microcosmexperiments conducted at the appropriate scale. Suchexperiments provide replication as well as greatercontrol over relevant variables which allows morerigorous hypothesis testing and important insight intomechanisms of biotic responses to pollutants. Wesuggest an appropriate use for stream microcosms inecotoxicology is in integrated assessment strategieswhere experimental results are linked with fieldmonitoring data. Under an integrated assessmentscenario, concordance of results between fieldobservations and dose-response exposures in microcosmscan provide important weight-of-evidence for guidancein management action or monitoring programs. We alsoidentify a number of other issues that must be addressedwhen utilizing stream microcosms; these includedecisions on exposure type, relative test duration,experimental design, biota source and type oftaxonomic assemblage, environmental realism, andchoice of end points. This kind of integratedassessment strategy has been applied to the Athabasca,Fraser, and Thompson Rivers in western Canada, wheremeasurement of similar end points in microcosms andfield sites has produced concordance of results and animproved understanding of causality instressor/response relationships.