Chapter 2 



Application of the Indicator Evaluation Guidelines to 

 Dissolved Oxygen Concentration as an Indicator of the Spatial Extent of 



Hypoxia in Estuarine Waters 



Charles J. Strobel, U.S. EPA, National Health and Environmental Effects 



Research Laboratory, Atlantic Ecology Division, Narragansett, Rl 



and James Heltshe, OAO Corporation, Narragansett, Rl 



This chapter provides an example of how ORD's indicator evaluation process can be applied to a simple 

 ecological indicator - dissolved oxygen (DO) concentration in estuarine water. 



The intent of these guidelines is to provide a process for evaluating the utility of an ecological indicator in 

 answering a specific assessment question for a specific program. This is important to keep in mind because 

 any given indicator may be ideal for one application but inappropriate for another. The dissolved oxygen 

 indicator is being evaluated here in the context of a large-scale monitoring program such as EPA's 

 Environmental Monitoring and Assessment Program (EMAP). Program managers developed a series of 

 assessment questions early in the planning process to focus indicator selection and monitoring design. The 

 assessment question being addressed in this example is What percent of estuarine area is hypoxic/anoxic? 

 Note that this discussion is not intended to address the validity of the assessment question, whether or not 

 other appropriate indicators are available, or the biological significance of hypoxia. It is intended only to 

 evaluate the utility of dissolved oxygen measurements as an indicator of hypoxia. 



This example of how the indicator evaluation guidelines can be applied is a very simple one, and one in 

 which the proposed indicator, DO concentration, is nearly synonymous with the focus of the assessment 

 question, hypoxia. Relatively simple statistical techniques were chosen for this analysis to illustrate the 

 ease with which the guidelines can be applied. More complex indicators, as discussed in subsequent 

 chapters, may require more sophisticated analytical techniques. 



Phase 1: Conceptual Relevance 



Guideline 1: Relevance to the Assessment 



Early in tlie evaluation process, it must be demonstrated in concept that the proposed indicator is 

 responsive to an identified assessment question and will provide information useful to a management 

 decision. For indicators requiring multiple measurements (indices or aggregates), the relevance of 

 each measurement to the management objective should be identified. In addition, the indicator should 

 be evaluated for its potential to contribute information as part of a suite of indicators designed to address 

 multiple assessment questions. The ability of the proposed indicator to complement indicators at other 

 scales and levels of biological organization should also be considered. Redundancy with existing 

 indicators maybe permissible, particularly if improved performance or some unique and critical information 

 is anticipated from the proposed indicator 



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