tailieunhanh - ECOTOXICOLOGY: A Comprehensive Treatment - Chapter 31

31 Descriptive Approaches for Assessing Ecosystem Responses to Contaminants INTRODUCTION Now that we have an appreciation of the important processes that characterize ecosystems and the general approaches used to quantify these processes, we will turn our attention to the primary objective of this section. As with community-level assessments, ecotoxicologists interested in ecosystem responses to anthropogenic stressors employ descriptive, quasi-experimental, and experimental approaches. In the following two chapters, we will explore the use of these observational and experimental studies to link changes in primary and secondary production, nutrient cycling, and decomposition to contaminants and other anthropogenic stressors. In a separate chapter, we will. | 31 Descriptive Approaches for Assessing Ecosystem Responses to Contaminants INTRODUCTION Now that we have an appreciation of the important processes that characterize ecosystems and the general approaches used to quantify these processes we will turn our attention to the primary objective of this section. As with community-level assessments ecotoxicologists interested in ecosystem responses to anthropogenic stressors employ descriptive quasi-experimental and experimental approaches. In the following two chapters we will explore the use of these observational and experimental studies to link changes in primary and secondary production nutrient cycling and decomposition to contaminants and other anthropogenic stressors. In a separate chapter we will consider effects of globally distributed and atmospheric stressors . acidification NO_f deposition elevated CO2 and UV radiation on these ecosystem processes. Investigations of ecosystem processes may be conducted across a range of spatial and temporal scales. Functional measures such as community metabolism or nutrient transport can be measured in isolated soil microbial systems or in whole forests or watersheds. However as we move up the hierarchy of biological organization from individuals populations communities ecosystems we generally increase the spatial and temporal scales of our investigations. Because many experimental studies of ecosystem processes are often limited in spatial and temporal scale descriptive approaches can provide very compelling and ecologically realistic results. As discussed in Chapter 23 for communities the typical trade-off is that observational or correlative investigations only provide a catalog of potential causal explanations. A more powerful case for causation in descriptive studies can be established by the application of strong inference Platt 1964 other formal inferential methods such as stressor identification Suter et al. 2002 or Bayesian inferential techniques. The initial