Similarity index values indicate that ecological changes between adjacent sites on the 

 same stream varied from un-measurable (>60%) to minor (40-60%) to moderate (20-40%). The 

 similarity- index ("percent community similarity") measures the cumulative percentage of cells of 

 each taxon that are shared by two stream sites. The two sites on Elk River had virtually identical 

 diatom assemblages. On the other hand, there was a very large change in the diatom assemblage 

 between the upper site on Blaine Spring Creek and the site below the fish hatchery. 



The diatom order Rhopalodiales includes genera [Epithemia and Rhopalodia) that are 

 known to harbor nitrogen-fixing endosymbionts within their cells. These symbiotic nitrogen- 

 fixers are single-celled cyanobacteria (blue-green algae). Nitrogen is likely the limiting nutrient 

 in waters that support large numbers of diatoms in the order Rhopalodiales. All of the sites in 

 this sample set supported less than 0.36% Rhopalodiales, which represents 3 or fewer valves in a 

 count of 800 valves. On this basis, there was no clear evidence of nitrogen limiting conditions at 

 any of the sites. 



The following paragraphs highlight the key findings for each stream and each site based 

 upon the major diatom species and core diatom metrics in Table 5. 



Antelope Creek. This site supported a large number of diatoms that are somewhat 

 tolerant of organic pollution. The pollution index here suggests minor impairment from organic 

 loading. An elevated number of motile diatoms also indicates minor sedimentation. Aside from 

 a few abnormal diatom cells, this site had excellent biological integrity and provided full support 

 of aquatic life uses. 



Elk River. Diatom metrics at the lower site suggest moderate impairment from 

 sedimentation and partial support of aquatic life uses. This was the only site in the sample set to 

 provide less than full support of aquatic life uses. The pollution index at this site was borderline 

 on minor impairment. At the upper site there was minor impairment from sedimentation but 

 otherwise excellent biological integrity. The two sites were virtually identical, floristically. 



10 



