rivers and inland lakes, from British Columbia south to Arizona, 

 and east to the Atlantic coast in North America, and in Chile in 

 South America; it appears to grow in situations receiving organic 

 inputs (Kociolek and Stoermer 1988) . 



The other two major diatom species in Bear Creek- -Fragi I aria 

 vaucheriae and Synedra ulna- -are somewhat tolerant of organic 

 pollution and nutrient enrichment (Lange-Bertalot 1979) . 

 Altogether, the major diatom species of Bear Creek indicate cool, 

 flowing, and circumneutral waters with moderate concentrations of 

 dissolved salts and algal nutrients (nitrogen and phosphorus) . 



With one exception, the diatom metrics of Bear Creek 

 indicated good to excellent water quality and full support of 

 aquatic life uses (Table 4) . Because of the large percent 

 abundance of Hannaea arcus (50.85%), the percent dominant species 

 metric slightly exceeded the threshold for moderate impairment. 

 Since Hannaea arcus may occasionally be found in large numbers in 

 relatively pristine waters (unpublished data) , its dominance in 

 Bear Creek may not be due entirely to cultural enrichment. 



The Shannon species diversity index was also a bit low in 

 Bear Creek (Table 4), owing in large part to dominance by Hannaea 

 arcus. The low diversity index indicated minor impairment but 

 still full support of aquatic life uses. 



Two teratological cells of Hannaea arcus were observed 

 during the diatom proportional count, indicating minor impairment 

 of aquatic life uses (Table 4) . Although diatoms in this family 

 (Fragilariaceae) are prone to deformities, these two abnormal 

 cells may nevertheless indicate chronic toxicity from heavy- 

 metals in Bear Creek. 



