Both sites on Spring Creek had excellent species richness, 

 even for a prairie stream (Table 6) . Diatom species diversity- 

 was excellent for a prairie stream at S-2 and good at S-3. 



,:' . • "■' 



The large number of Achnanthes minutissima at S-3 resulted 

 in a rating of moderate impairment and partial support of aquatic 

 life uses. The reasons for this rating were borderline values 

 for percent dominant species and the disturbance index. 



Achnanthes minutissima is an opportunistic "weed" species 

 that is among the first to colonize recently disturbed areas 

 (Barbour et al . 1999) . Disturbance may be caused by physical 

 scour, chemical toxicity, or macroinvertebrate grazing. If this 

 Spring Creek is typical of most spring creeks, it supports an 

 abundance of grazing fauna, including snails. In the absence of 

 fast currents and heavy metals or other toxics in Spring Creek, 

 the disturbance indicated at S-3 is probably biological and 

 natural in origin. 



Siltation index values were very low, especially for a 

 prairie stream (Table 6) . No abnormal cells were encountered in 

 the diatom proportional counts, indicating the probable absence 

 of toxics or physiological stressors. The percentage of cells in 

 the family Epithemiaceae was low to moderate, indicating low to 

 moderate levels of inorganic nitrogen. 



The two sites shared only about 32 percent of their diatom 

 assemblages. Since there is no evident tributary or surface 

 discharge in the reach between these sites (Map 1) , their quite 

 different floras may result from intervening springs (Agency 

 Spring?) or zones of upwelling water originating from the Teton 

 River. Spring Creek has all the characteristics of a spring 

 brook of the Teton River. 



