PNNL

Abstract

Here we ask what types of field studies can best detect interactions among stressors and allow us to separate and rank the relative importance of individual stressors in systems receiving multiple disturbances (natural and/or anthropogenic). If multiple stressor responses are common in nature, then single variable tests, such as analysis of a biomarker in isolation or along a surmised gradient, or studies that exclude variables other than pollutants, could be insensitive to all but the most extreme influences of contamination. Preponderance of evidence approaches will be similarly insensitive if designs are too simplistic. A combination of persistent and intensive study of exposure and response in the field, study of critical ecosystem-specific and organism-specific processes, as well as iteration with experimental studies, are useful (and perhaps necessary) strategies to discern interactions among stressors. As our understanding of the mechanisms responsible for changes at lower levels of organization improves, responses to complex stressors become more predictable. This improved mechanistic understanding could lead to a similar degree of understanding for responses at higher levels of biological organization. Below we discuss three examples where researchers have attempted to identify and quantify the relative importance of individual stressors in systems receiving complex stressors. The first example demonstrates how intensive field studies identified multiple stressors and how a management plan resulted in mitigation of these stressors. The second example describes a series of field experiments designed to identify the relative importance of water quality and substrate quality on benthic macroinvertebrates in a metal-polluted stream. The final example illustrates the difficulty of sorting out the direct and indirect influences of global climate change on populations.