Coal Region of Montana, this species (misidentif ied as Navicula 

 pavillardii) prefers brackish, sodium sulfate waters, water 

 temperatures between 21 and 3 0''C, coarse sand substrates, and pH 

 values greater than 8.10; it also tolerates some suspended 

 sediment, turbidity, and chloride (Bahls et al . 1984). 



The relative abundance of Navicula durrenbergiana and other 

 pollution tolerant diatoms in Careless Creek resulted in a 

 marginal pollution index that indicated minor impairment but 

 still full support of aquatic life uses (Table 5) . 



The relative abundance of diatoms in the genera Navicula and 

 Nitzschia resulted in a siltation index value of 45.14 (Table 5) . 

 This is a normal but marginal value for least -impaired prairie 

 streams. Careless Creek is classified C-3 at the sampling site, 

 but it is classified B-l about -10 miles upstream from this point, 

 above its confluence with Swimming Woman Creek (Montana Surface 

 Water Quality Standards 1994) . Careless Creek near its mouth has 

 elements of both a cold-water and a warm-water flora, indicating 

 that the stream here might be more appropritatelay classified as 

 B-2. If such were the case, the siltation index would indicate 

 moderate impairment and only partial support of aquatic life. 



Careless Creek supported a modest number of cells in the 

 diatom family Epithemiaceae , and the largest relative abundance 

 of diatoms in this family of the three streams addressed in this 

 report (Table 5) . This would indicate that, of the three 

 streams, nitrogen would more likely be the limiting nutrient in 

 Careless Creek than in the other two streams. 



Lodqepole Creek 



Diatom diversity and species richness in Lodgepole Creek 

 were excellent, but a large percentage of pollution tolerant 

 diatoms and a large percentage of diatoms in the genera Navicula 



10 



