Diatom species richness and diversity were excellent for a 

 mountain stream and good for a prairie stream (Table 6) . The 

 percent dominant species indicated minor stress at both sites. 

 The relatively low percentage of Achnanthes minutissima, an 

 opportunistic pioneer species, indicated minimal biological, 

 chemical, or physical disturbance at both sites. 



The relatively large number of cells in the motile genera 

 Navicula and Nitzschia indicated moderate impairment from 

 siltation at both sites (Table 6) . However, when compared to 

 diatom criteria for prairie screams, siltation caused only minor 

 impairment at C 1 and no impairment at C 2 . 



No diatom cells exhibiting physical abnormalities were 

 observed at site C 1. Nine (9) abnormal cells representing four 

 species were counted at C 2 , indicating moderate impairment at 

 this site. The percentage of teratological cells has been 

 correlated with ambient concentrations of heavy metals in certain 

 Colorado streams (McFarland et al . 1997). Teratological cells 

 may also result from other forrris of pollution and environmental 

 stress . 



No diatom species in the family Epithemiaceae were counted, 

 indicating that nitrogen was probably not limiting to algal 

 growth at either site. Diatoms in this family often harbor 

 nitrogen-fixing cyanobacteria within their cells and are most 

 often found in waters where nitrogen is the limiting nutrient. 



The relatively low similarity index (41.52) indicated that 

 the two sites had only somewhat similar diatom floras and that a 

 moderate amount of change had occured between the two sites. 

 Adjacent reaches on the same stream, without intervening 

 tributaries or pollution sources, can expect to have at least 60% 

 of their diatom floras in common (Bahls 1993) . 



