AbstractWetlands represent unique environments for assessing ecological risks. Habitats may vary from riverine to basin type and include such diverse media as surface waters, sediments, soils, and ground water, with both terrestrial and aquatic biota. Given the diversity of wetland habitats, a number of species may be expected to be fairly unique to a particular site. Wetland ecosystems may be impacted by chemical contamination or by nonchemical stressors such as temperature or suspended solids. A key to assessing ecological risks to chemically contaminated wetlands is determining the degree of contaminant bioavailability from multiple environmental media. Chemical and physical factors of the various wetland habitats must be evaluated for their role in chemical release, transformation, and availability. Approaches to assessing ecological risks may extend from simple benchmark or literature comparisons to direct measurement of exposure and toxicity through laboratory and/or field tests. To increase the utility of wetland risk assessments, the uncertainty inherent in the complex habitats and in the chemistry that governs contaminant bioavailability should be minimized. This can be most readily accomplished by applying an assessment methodology triad of ecology, chemistry, and toxicology to characterize ecological risks. Literature toxicity information and laboratory and field data are used to evaluate potential threats to individuals or species in each trophic level of the wetland food web. The ecological data are integrated with this information to assess whether the concentrations of contaminants and the observed or predicted toxicity relate to actual ecological effects. The ecological relevance of the expected or measured biological responses is of prime importance in predicting risks to the wetland ecosystem. Applications of this approach to risk assessments are presented as case studies of metals‐contaminated wetlands at Milltown Reservoir, Montana, and Kesterson Reservoir, Californi
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