upstream site. The pollution index value at the downstream site was close to the threshold for 

 minor impairment. Like Planothidium lanceolatum at the upstream site, the dominant species at 

 the downstream site — Encyonema silesiacum — is somewhat tolerant of organic loading. The 

 two sites on Meadow Creek shared about half of their diatom floras, indicating that only a small 

 amount of floristic and environmental change occurred between them. 



Martin Creek. Elevated siltation index values indicated minor impairment from 

 sedimentation at both sites on Martin Creek. Both sites also supported a few teratological 

 valves, indicating possible chronic toxicity from heavy metals or some other stressor. The 

 pollution index was acceptably high at both sites, indicating little organic loading. The dominant 

 species at both sites was Cocconeis placentula, a species adapted to living on rocks and other 

 hard surfaces. The two sites shared almost three-quarters of their diatom assemblages, which 

 indicate virtually no floristic or ecological difference existed between them. 



Reimel Creek. Both sites on Reimel Creek supported an elevated number of pollution- 

 tolerant diatoms for a mountain stream, indicating minor impairment from organic loading. Such 

 common pollution-tolerant species as Nitzschia archibaldii, Planothidium dubium, Planothidium 

 lanceolatum, and Synedra ulna were common in Reimel Creek. The siltation index at the 

 downstream site exceeded the threshold for moderate impairment and partial support of aquatic 

 life uses. At the upstream site, the siltation index approached but did not exceed the threshold 

 for minor impairment. However, the large number of diatoms in the genus Planothidium at the 

 upstream site indicated a sandy substrate here. The two sites on Reimel Creek shared less than 

 half of their diatom associations, indicating minor to moderate change occurred between them. 



Ditch Creek. Other than an elevated number of Achnanthidium minutissimum, diatom 

 metrics indicated excellent biological integrity and full support of aquatic life uses in Ditch 

 Creek. The stress registered here is probably natural in origin and related to steep gradients, fast 

 current velocities, cold temperatures, and low nutrient concentrations. 



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