1^ living on sand grains and collectively they indicate a sandy substrate. The other major species — 

 Nitzschia linearis and Synedra ulna — indicate human disturbance and eutrophication. Nitzschia 

 linearis is highly motile and adapted to living on shifting substrates. Charcoal Gulch did not 

 support any teratological diatom cells. 



Elkhorn Creek. Large percentages of abnormal diatom cells (>10%) suggest severe 

 impairment from toxic metals at both sites on Elkhorn Creek. Moreover, diatom species 

 diversity at these sites was significantly lower than all of the other sites in the sample set. Both 

 sites were dominated by Achnanthidium mimitissimum. This species tolerates elevated 

 concentrations of heavy metals and, when present in large numbers, indicates probable physical, 

 chemical, and/or biological disturbance. Two pollution-tolerant species of Fragilaria were also 

 among the major species at site 02. Sites 01 and 02 were virtually identical, floristically. 



Francis Creek. Diatom metrics indicate minor impairment from sedimentation at both 

 sites and minor impairment from organic loading at site 01. This organic loading may be natural 

 in origin. Major species at site 01 show the influence of upstream lakes or ponds (Aulacoseira 

 alpigena), elevated inorganic nutrients {Melosira varians), sandy substrates {Planothidium spp.), 

 and low current velocities {Staurosira construens). An abundance of unattached diatoms 

 {Pseudostaurosira brevistriata, Staurosira construens) also indicates a gentle gradient at site 02. 

 The other major species at site 02 {Epithemia sorex) is a nitrogen fixer and indicates low ambient 

 concentrations of biologically available nitrogen. Abnonnal diatom cells were not observed at 

 either site. The two sites shared less than one-third of their diatom assemblages, indicating that a 

 moderate amount of environmental changes occurred between them. 



Divide Creek. Minor organic loading and minor, approaching moderate sedimentation 

 was indicated at site 01 on Divide Creek. The major diatom species here indicate alkaline and 

 eutrophic waters. Although no impairment was noted at site 02, both the pollution index and the 

 siltation index approached ihcir respective thresholds for minor impaimient. The appearance of 

 Planothidium species and Cocconeis placentula among the major species at site 02 suggests the 

 presence of sandy substrates. No abnonnal diatom cells were observed at either site. They 

 A shared less than half of their diatom assemblages. 



14 



