adverse ecological effects: Changes that are considered undesirable because they alter valued structural or functional characteristics of ecosystems or their components. An evaluation of adversity may consider the type, intensity, and scale of the effect as well as the potential for recovery.

assessment: The analysis and transformation of environmental data into policy-relevant information that can assist decision-making and action.

assessment endpoint: An explicit expression of the environmental value that is to be protected, operationally defined by an ecological entity and its attributes. For example, salmon are valued ecological entities; reproduction and age class structure are some of their important attributes. Together "salmon reproduction and age class structure" form an assessment endpoint.

characterization of ecological effects: A portion of the analysis phase of ecological risk assessment that evaluates the ability of a stressor(s) to cause adverse effects under a particular set of circumstances.

characterization of exposure: A portion of the analysis phase of ecological risk assessment that evaluates the interaction of the stressor with one or more ecological entities. Exposure can be expressed as co-occurrence or contact, depending on the stressor and ecological component involved.

conceptual model: A conceptual model in problem formulation is a written description and visual representation of predicted relationships between ecological entities and the stressors to which they may be exposed.

ecological risk assessment: An ecological risk assessment evaluates the potential adverse effects that human activities have on the plants and animals that make up ecosystems. The risk assessment process provides a way to develop, organize and present scientific information so that it is relevant to environmental decisions. When conducted for a particular place such as a watershed, the ecological risk assessment process can be used to identify vulnerable and valued resources, prioritize data collection activity, and link human activities with their potential effects.

exposure: The contact or co-occurrence of a stressor with a receptor.

exposure scenario: A set of assumptions concerning how an exposure may take place, including assumptions about the exposure setting, stressor characteristics, and activities that may lead to exposure.

exposure profile: The product of characterization of exposure in the analysis phase of ecological risk assessment. The exposure profile summarizes the magnitude and spatial and temporal patterns of exposure for the scenarios described in the conceptual model.

indicator: A measurement that can be used to assess the condition, status or trends of an ecological resource. The term is widely used in water resources management programs, but has many different interpretations. It is preferable in risk assessment to avoid using the term indicator and instead use the more specific terms measure of effect, measure of exposure, and assessment endpoint, as appropriate.

measure of effect (measurement endpoint): A change in an attribute of an assessment endpoint or its surrogate in response to a stressor to which it is exposed.

measure of exposure: A measure of stressor existence and movement in the environment and its contact or co-occurrence with the assessment endpoint.

measurement endpoint: See "measure of effect."

problem formulation: The first phase of ecological risk assessment, which includes a preliminary description of exposure and ecological effects, scientific data and data needs, key factors to be considered, and the scope and objectives of the assessment. This phase produces the risk hypotheses, conceptual model and analysis plan, around which the rest of the assessment develops.

risk analysis phase: A phase of ecological risk assessment consisting of two main parts: 1) characterization of ecological effects— evaluating the ability of a stressor(s) to cause adverse effects under a particular set of circumstances, and 2) characterization of exposure— evaluating the interaction of the stressor with one or more ecological entities.

risk characterization phase: A phase of ecological risk assessment that integrates the exposure and stressor response profiles to evaluate the likelihood of adverse ecological effects associated with exposure to a stressor. Lines of evidence and the adversity of effects are discussed.

risk estimation: Ideally, the conclusions of the risk characterization phase expressed as some type of quantitative statement (e.g., there is a 20% chance of 50% mortality under the circumstances assessed), but often expressed as a qualitative statement (e.g., there is a high likelihood of mortality occurring).

risk management: The process of evaluating and selecting action alternatives in response to risk assessment findings.

stressor: Any physical, chemical, or biological entity that can induce an adverse response (synonymous with agent).

stressor-response curve: A graphic, quantitative representation of the relationship between a stressor (such as a pesticide concentration in the water column) and an ecological effect (such as mortality of a given fish species if exposed to different concentrations of the pesticide).

stressor-response profile: The product of characterization of ecological effects in the analysis phase of ecological risk assessment. The stressor-response profile summarizes the data on the effects of a stressor and the relationship of the data to the assessment endpoint.

stressor source: An entity or action that releases to the environment or imposes on the environment a chemical, physical, or biological stressor or stressors.

uncertainty analysis: Part of the risk assessment process that describes, either quantitatively or qualitatively, the relative magnitude of uncertainties and their implications for the assessment.