Applied Wetlands Science - Chapter 4

Kent, David J. et al “Ecological Risk Assessment of Wetlands” Applied Wetlands Science and Technology Editor Donald M. Kent Boca Raton: CRC Press LLC,2001 CHAPTER 4 Ecological Risk Assessment of Wetlands David J. Kent, Kenneth D. Jenkins, and James F. Hobson CONTENTS The Human Health Risk Assessment Paradigm Ecological Risk Assessment The Ecological Risk Assessment Framework Problem Formulation Phase Choosing Biological Endpoints Spatial and Temporal Considerations Other Considerations Analysis Phase Exposure Characterization Ecological Effects Characterization Risk Characterization Phase Predictive Ecological Assessments Problem Formulation Exposure Characterization Ecological Effects Characterization Risk Characterization The Quotient Method for Risk Characterization Retrospective Ecological Assessments Problem Formulation Exposure Characterization Ecological Effects Characterization Risk Characterization Summary References ©2001 CRC Press LLC Until recently, the term risk assessment generally was applied to the estimate of risk to human health, typically from chemical exposure. For example, a cancer risk assessment is an estimate of the risk to humans from carcinogenic compounds. Recently, however, the term risk assessment has been applied to ecological systems. An ecological risk assessment is an estimate of the adverse effect to an ecosystem from chemical, physical, or biological stressors resulting from anthropogenic activ-ity. This recent interest in assessing ecological health is evidenced by several pub-lications (Bartell et al., 1992; Cairns et al., 1992; Suter, 1993; Newman and Strojan, 1998; Lewis et al., 1999) including two documents produced by the U.S. Environ-mental Protection Agency (USEPA, 1992, 1998). The first of these USEPA docu-ments, Framework for Ecological Risk Assessment (1992), was intended as the first step in a long-term program to develop guidelines for the performance of ecological risk assessments. The second document, Guidelines for the Ecological Risk Assess-ment, provided more detailed information and is the current guidance on the subject. The principles of ecological risk assessment can be applied to any ecosystem, although theymay be particularly relevant to wetlands. The extent and rate of wetland loss, as well as the biologic, economic, and social importance of wetlands, are well documented (Mitsch and Gosselink, 1986). Moreover, the transitional nature of wetlands may make them especially sensitive to stress. Despite the uniform appli-cation of assessment principles to ecological systems, individual wetlands are suf-ficiently different in their spatial, temporal, and physiochemical characters to warrant site-specificsamplingandanalysis(Figures1and2).Thesedifferenceswillinfluence the design and interpretation of the ecological risk assessment. Figure 1 Risk assessment can be broadly applied to a variety of ecosystems.Nevertheless, individual wetlands are sufficiently different in their spatial, temporal, and physic-ochemical characters to warrant site-specific samping and analysis. A New England saltmarsh is shown here. ©2001 CRC Press LLC Figure 2 An Arkansas riverine system wetland. To understand the use of ecological risk assessment for wetland ecosystems, an introduction to the principles of risk assessment is necessary. The current basis for risk assessment is derived from the National Research Council Risk Assessment paradigm (1983). Following this, an in-depth discussion of the USEPA Ecological Risk Assessment Framework (USEPA, 1992) is presented as is a discussion of the challenges and strategies associated with carrying out assessments. Finally, examples of specific applications to wetland ecosystems are provided. THE HUMAN HEALTH RISK ASSESSMENT PARADIGM The risk assessment paradigm has been used for some time to evaluate the chronic impacts of environmental pollutants on human health. This strategy was initially conceptualized by the National Research Council Risk Assessment Panel (NRC, 1983) and formalized by the USEPA in its 1986 Guidelines (USEPA, 1986a–e). This risk assessment paradigm consists of several components: ©2001 CRC Press LLC • Hazard identification: does a chemical contaminant represent a specific threat to human health? Establishment of cause–effect relationships is central to this com-ponent. • Defining dose–response: what is the relationship between the magnitude of the exposure and the probability of an adverse health effect? • Exposure assessment: what is the potential for human exposure to the chemical of concern? • Risk characterization: what is the potential magnitude of risk to human health given the predicted exposure and dose–response data? What is the uncertainty associated with this risk estimate? Standard methodologies are employed to evaluate potential threats to human health. The methodologies usually involve determining all relevant effects and then summing those effects to get a total effect value. ECOLOGICAL RISK ASSESSMENT Ecological risk assessments (ERA) examine the probability that undesirable ecological effects are occurring or may occur as a result of exposure to a stressor or a combination of stressors. The term stressors is used here to reflect the broad range of anthropogenic factors that can result in ecological perturbations. Stressors may include any chemical, physical, or biological factor resulting from anthropo-genic activities that can cause an ecological disturbance. Most often, however, the term stressor refers to toxic chemicals. ERAs can be used to address a wide range of issues and are generally classified as predictive or retrospective. Predictive ERAs are designed to assess the risks associated with proposed actions, such as the introduction of new chemicals into the environment and the establishment of new sources of stressors or hypothetical accidents (USEPA, 1991). Predictive risk assessments have usually followed the NRC human health paradigm relatively closely while emphasizing the choice of biological endpoints and related stressor–response data. In contrast, retrospective ERAs address the risks associated with stressors released due to current or previous anthropogenic activities. Examples of retrospective assess-ments include evaluating the ecological impact of hazardous waste sites and previous releases or spills. The goal of this type of risk assessment is to establish and define the relationship between the pollution source, the distribution of stressors, the expo-sure of biological endpoints, and the level of effects of this exposure on the ecosystem. Retrospective assessments often take advantage of field data to define contaminant sources and measure adverse biological effect. Various levels of data collection or site-specific assessment may be necessary to provide the information required to design and conduct the retrospective ecological risk assessment, and to achieve a given level of confidence. The challenge here is to establish cause–effect relationships between the source of stressors and any observed ecological effects. Some ERAs, such as those used for wetlands, may involve both predictive and retrospective aspects. For example, in an assessment of a hazardous waste site, the ©2001 CRC Press LLC ... - tailieumienphi.vn