be the limiting nutrient at these sites. Cyanobacteria were absent from the lower sites on East 

 Redwater River. 



The filamentous chrysophyte Tribonema is known to favor cool water temperatures. 

 Tribonema was common in samples collected from RDWEC03 and upper Horse Creek and 

 upper Pasture Creek. 



Diatoms (Table 4) 



Of thel 1 major diatom species in the study area, only Rhoicosphenia abbreviate is 

 sensitive to organic pollution (class 3). Four of the major species are most tolerant of organic 

 pollution (class 1). These species were most abundant at the upper East Redwater site and in 

 Horse Creek. The remaining 6 major species are somewhat tolerant of organic pollution and 

 these (class 2) species were abundant at all sites except upper Horse Creek (Table 4). 



East Redwater River. A large percentage of highly motile diatoms resulted in moderate 

 impairment from sedimentation and partial support of aquatic life uses at sites 04 and 02. A low 

 pollution index and low species richness also indicated moderate impairment at the upper site 

 (04). The dominant species here were Navicula veneta and Nitzschia aurariae. Both of these 

 species are tolerant of high levels of BOD5 and dissolved solids, hence the most likely causes of 

 impairment at site 04 are excessive sedimentation, organic loading, and salinity. 



Extremely low species richness and diversity values indicate severe stress for a prairie 

 stream at site 03 (Table 4). Rhoicosphenia abbreviata accounted for nearly 60% of the diatom 

 assemblage at this site. This autotrophic, alkaliphilous, periphytic diatom prefers cool, flowing 

 waters, fairly high levels of dissolved oxygen, and large amounts of inorganic nutrients (Van 

 Dam et al. 1994). Although initially believed to be an "oligohalobe" (Patrick and Reimer 1966), 

 Krammer and Lange-Bertalot (1986) report it from "electrolytically rich to brackish inland 

 waters and seacoasts". They also observe it to be a "guter Verschmutzungsindikator" (good 

 pollution indicator) of moderate organic loading. R. abbreviata most likely flourished here 

 because of higher current velocities, cooler waters, and lower concentrations of dissolved solids 



