Collar Gulch. The headwaters site on Collar Gulch supported a unique and very simple 

 diatom assemblage consisting mostly of Eunotia arcus. Pinmilaria subcapitata, and Fnistulia 

 saxonica. These are acidobiontic, acidophilous, and circumneutral diatoms, respectively, with 

 regard to their pH preference (Van Dam et al. 1994). Their abundance here suggests prevailing 

 pH values that range from less than 5.5 to around 7.0. Although no abnormal diatom cells were 

 observed at this site, the three dominant species listed above are not as inclined to produce 

 abnormal cells as diatoms in the family Fragilariaceae (e.g., Synedra nimpens). The extremely 

 low species richness and diversity values here suggest severe stress by acidity, if not by a 

 combination of acid waters and elevated heavy metals. 



The middle site (near Collar Peak) was dominated hy Achnanthidium minutissimum, an 

 indicator of disturbance and a species that tolerates elevated concentrations of heavy metals. The 

 extremely low species richness and diversity values and the large percentage of abnormal cells 

 confirm that this site is severely stressed by heavy metals. This site shared less than 1% of its 

 diatom assemblage with the headwaters site, which indicates a major change in environmental 

 conditions between the two sites. Since Achnanthidium minutissimum prefers circumneutral to 

 alkaline waters, this change was probably due to an increase in pH. 



Although diatom species richness and diversity were somewhat higher at the lower site, 

 this site supported a much larger percentage (>I3%) of abnormal diatom cells, which suggests 

 severe impairment by heavy metals. Like the middle site on Chicago Gulch, this site was 

 dominated by Synedra rumpens. This diatom prefers pH values around 7.00 and is known to 

 tolerate elevated concentrations of heavy metals. Synedra nimpens has a tendency to produce 

 abnormal cells when exposed to heavy metals. In addition, a depressed pollution index suggests 

 minor impairment from organic loading at the lower site. This site shared only 22% of its diatom 

 assemblage with the middle site, which indicates that a moderate to major change in the diatom 

 flora and in environmental conditions occurred between the two sites. 



