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fresh waters (Palmer 1977). Vaucheria was also abundant here. 

 The two samples from the mouth of Squirrel Creek contained very 

 similar non-diatom floras. Only one common genus {Oedogonium) 

 did not appear in both samples . 



DIATOMS 



Upper Squirrel Creek (#4) supported a large number of diatom 

 species (68) and individuals were equitably distributed among the 

 species: the dominant diatom species accounted for less than a 

 quarter of the cells and the diversity index was a healthy 4.34 

 (Table 5) . Except for a slightly depressed pollution index, all 

 of the diatom metrics at site #4 indicated excellent biological 

 integrity and no impairment when compared to other prairie 

 streams. Upper Squirrel Creek site #4 proved to be a suitable 

 local reference site for use in Protocol II (see below) . 



The number of diatom species in Squirrel Creek declined by 

 more than half from site #4 to site #3 at the culvert, to a 

 minimum of 28 species (Table 5) . Together with an elevated 

 siltation index, this low species richness indicated moderate 

 stress and only fair biological integrity. Increases in the 

 percent abundances of Achnanthes lanceolata, Navicula gregaria, 

 and Navicula veneta (all pollution-tolerant diatoms) probably 

 indicate a significant increase in the concentration of nutrients 

 and dissolved ions between sites #4 and #3. These two sites were 

 very different f loristically : they shared less than a quarter of 

 their diatom floras. 



Diatom species richness and diversity rebounded somewhat at 

 the mouth of Squirrel Creek (#1) , although siltation index values 

 were still on the threshold of moderate impairment (Table 5) . 

 The diatom assemblage here was dominated by Navicula gregaria. 

 This species tolerates a wide range of conductivities, from fresh 



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