ABSTRACT

This chapter describes the use of field study designs and in situ methods for causal assessment. It discusses study designs, in situ methods, and the less common approach of whole ecosystem experiments. Effective studies are designed to sample a range of different exposures of interest and minimize the influences of confounding factors. In situ methods provide additional opportunities to control exposures and reduce variability in biological responses. When these strategies are used together, they can produce high-quality evidence of cause and effect relationships. Field studies can be specifically designed to elucidate mechanisms, demonstrate concentrations, and other conditions that are necessary for effects to occur. Results of studies conducted at sites other than the one under investigation can be applied when it can be claimed that the environmental setting, stressors, and biota are similar enough that the same results would occur.