100 



90 -- 



■ 80 -- 



S 70-- 



< 60 -- 



1 50- 



y 40 -- 



a. 



30 -- 

 20 - 



10 -- 







± 



i: 



± 



-^ 



-^ 



D <2mg/L 



D <5 mg/L 



'90 



■91 



'92 

 Year 



•93 



"90-93 



Figure 2-8. Annual estimates of percent area hypoxic in tiie Virginian Province based on 



EMAP dissolved oxygen measurements and criteria of < 2 mg/L and > 5 mg/L. 

 '90-93 represents the four-year mean. Error bars represent 95% confidence 

 intervals. 



Figure 2-9. Climatic conditions in the Virginian Province, 1990-1993. (A) deviation from 

 mean air temperature, and (B) deviation from mean rainfall. 



Guideline 11: Spatial Variability 



Indicator responses to various environmental conditions must be consistent across the monitoring 

 region if that region is treated as a single reporting unit. Locations within the reporting unit that are 

 known to be in similar ecological condition should exhibit similar indicator results. If spatial variability 

 occurs due to regional differences in physiography or habitat, it may be necessary to normalize the 

 indicator across the region, or to divide the reporting area into more homogeneous units. 



2-13 



