Diatoms (Table 5) 



Three of the major diatom species in Careless Creek are sensitive to organic pollution. 

 One {Achnanthidium minutissimum) was abundant only below the return and near the mouth, 

 while the other two (Fragilaria atomus and Staurosira construens) were abundant only at the 

 upper site (Table 5). A. minutissimum is an attached species and prefers fresher waters such as 

 those released from Deadman's Basin. F. atomus and S. construens are free-living, non-motile 

 species that grow best in quiet or slow-moving waters. F. atomus is also adapted to living in 

 waters of higher conductivity. 



Five of the major species are somewhat tolerant of organic pollution and these were 

 present at all three sites. Nitzschia reversa, a somewhat tolerant species that lives in the plankton 

 of prairie stream pools, was abundant only at the upper site, suggesting that this site had slower 

 current velocities than the lower sites. One of the major diatom species in the 2003 samples 

 from Careless Creek — Navicula duerrenbergiana — is most tolerant of organic pollution 

 (pollution tolerance class 1). This motile species is adapted to living on unstable substrates of 

 fine sediment and was found only at the lower site near the mouth, where it was abundant. 



When compared to criteria for mountain streams in Table 2, diatom metrics suggest that 

 the upper and lower sites are moderately impaired by organic loading and the middle site was 

 slightly impaired (Table 5). Elevated percentages of motile diatoms also indicate moderate 

 impairment from sedimentation at the upper site and minor impairment at the lower two sites. 

 However, if these same metric values are compared to criteria for prairie streams in Table 3, 

 there is no impairment from sedimentation and only minor impairment from organic loading. 

 This is because higher levels of sedimentation and organic loading are naturally present in prairie 

 streams. All three sites are classified as prairie (C-3) sites. 



Diatom species richness and diversity values were good to excellent at all three sites for 

 both mountain and prairie streams. The sites above and below the Deadman's Basin return 

 shared only about 30% of their diatom assemblages, which suggests that there was a moderate 

 change in environmental conditions between them. The middle and lower sites, however, shared 

 almost 60% of their diatom floras, which suggests little or no change between them. 



