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Modal Categories (Table 5) 



Several ecological attributes assigned by Stevenson and Van Dam et al. (1994) were 

 selected from the diatom reports in the appendix and modal categories of these attributes were 

 extracted to characterize water quality tendencies in Sullivan and Skyland Creeks (Table 5). 



The majority of diatoms at both sites on Sullivan Creek were non-motile autotrophs that 

 tolerate high concentrations of organics and indicate alkaline and fresh-brackish waters with 

 continuously high dissolved oxygen. However, the percentage of diatoms in the "continuously 

 high" category declined significantly from the upstream site to the downstream site, indicating a 

 decline in the availability of dissolved oxygen. The modal categories for saprobity and trophic 

 state each shifted two levels between the upstream and downstream sites, indicating significant 

 increases in organic loading and concentrations of inorganic nutrients. 



In Skyland Creek, the modal category for oxygen demand was "moderate", indicating 

 even less available dissolved oxygen here than in lower Sullivan Creek. The modal category for 

 saprobity in Skyland Creek was alpha-mesosaprobous, which is the same modal category that 

 was recorded at the lower site on Sullivan Creek (Table 5). The alpha-mesosaprobous category 

 indicates waters with 25-70% oxygen saturation and 4-13 mg/L BOD (Van Dam et al. 1994). 



