at this site. These are attributes that are more common in mountain streams, where diatom 

 species richness and diversity tend to be lower. In terms of overall water quality, this site was 

 superior to the upstream site (04), with which it shared only 16% of its diatom assemblage. 



Besides moderate impairment from sedimentation, site 02 had a slightly depressed 

 pollution index, indicating minor to moderate impairment from organic loading. The dominant 

 species here {Cydotella meneghiniana, Navicula recens, Nitzschia frustulum) are only somewhat 

 tolerant of organic pollution and elevated dissolved solids. Though present here, the pollution 

 tolerant species Navicula veneta and Nitzschia aurariae were much less abundant than they were 

 upstream at site 04. Site 02 shared only about 31% of its diatom assemblage with the next 

 upstream site (03), which indicates that a moderate change in environmental conditions occurred 

 between the two sites. 



The diatom assemblage from the East Redwater River near its mouth (site 01) was very 

 similar to the assemblage at station 03 in that it was dominated by Rhoicosphenia abbreviata 

 (Table 4). Like station 03, this site likely had higher current velocities, cooler waters, and lower 

 concentrations of dissolved solids than other sites. Hence, the moderate stress noted here was 

 probably natural and related to superior water quality (for a prairie stream) rather than to some 

 form of pollution. The diatom assemblages at sites 01 and 03 have much in common with 

 diatom assemblages from mountain streams. Although site 01 shared only about 35% of its 

 diatom assemblage with the next upstream site (02), it shared 72% of its diatom assemblage with 

 site 03. The fact that these sites were sampled early in the season, just before the summer 

 sampling season, might also help to explain why they supported unusually high percentages of 

 Rhoicosphenia abbreviata and low species richness and diversity values. 



Horse Creek. Diatom metrics indicate moderate organic loading at both sites, moderate 

 sedimentation at the upper site, and severe sedimentation at the lower site (Table 4). (Note: 

 some sedimentation and internal organic loading may be natural in prairie streams.) Diatom 

 species richness, diversity, and equitability values were low to moderately low at the two sites. 

 The cause of this low diversity is likely a combination of organic loading and excessive salinity. 

 Some of the most common diatom species in Horse Creek {Navicula veneta, Nitzschia aurariae. 



