Multiple Stressors

There is a pressing need for developing and testing a general set of theories in order to provide a confident basis for prediction of multiple stressor effects.Confident prediction is central to confident decision making in water pollution control.Consequently, WERF commissioned this study which has as its goal to provide a study design based on good science that helps establish a general, conceptual approach to multiple stressors.The objectives of the study are to develop a flexible and scientifically defensible conceptual model of the environmental effects of multiple stressors on river and stream ecosystems; develop a study design to test the conceptual model of multiple stressor effects; and, document the process used to arrive at the conceptual model.The multiple stressor conceptual model includes two main components: (1) a diagram that portrays the main features of the study team's understanding of how multiple stressors would interact and the nature of the effects; and (2) a series of three testable risk hypotheses.These two components follow the guidance provided by the U.S.EPA for ecological risk assessment. The proposed conceptual model encompasses the following key assumptions: interactions between the stressor and the ecosystem are dependant upon the existing baseline conditions; for each stressor/baseline combination there will theoretically be a functional and a structural response; effects on habitat are caused by structural or functional responses to stressors; and effects on habitat can cause structural or functional responses.