Summary 



The results of this evaluation show that point-in-time bottom dissolved oxygen measurement can be an 

 appropriate indicator for determining the spatial extent of hypoxia in a regional monitoring program. The 

 indicator is conceptually relevant to both the assessment question and ecological function. It is easily 

 implemented at reasonable cost with well-defined methods. Probably the greatest concern in the 

 implementation of this indicator is the temporal and spatial variability of DO concentrations. This variability 

 limits the utility of point-in-time measurements in describing the conditions at a given station. However, 

 when the indicator is applied across a large region to generate an estimate of the overall percent area 

 hypoxic, this evaluation indicates reasonable stability of the indicator. This scale-dependent conclusion 

 clearly illustrates the need to evaluate an indicator in the context of a specific monitoring program, as an 

 indicator that may be ideal for one type of program may be inappropriate for another. In this case, the 

 indicator itself could be applied to monitoring programs designed to characterize conditions at individual 

 stations if alternative methods were employed (e.g., continuous monitoring). Lastly, dissolved oxygen data 

 are easily interpretable relative to the assessment question on the extent of hypoxia, and are of high value 

 to environmental managers. 



Acknowledgements 



This work was supported in part by EPA contract number 68-W5-0065 to OAO Corporation. This chapter is 

 NHEERL-Atlantic Ecology Division contribution # NHEERL-NAR-2068. 



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