• 



The modal category' for pH at all of the sites was either circumneutral or alkaliphilous, 

 except at the upper site on Coal Creek, where the modal category was alkalibiontic. While 

 alkaliphilous diatoms prefer pH values greater than 7, alkalibiontic diatoms require pH values 

 greater than 7. The higher pH in upper Coal Creek may have been transient and due, in part, to a 

 large standing crop of algae undergoing photosynthesis. All of the sites were rated as fresh- 

 brackish (<900 mg/L dissolved solids) except the lower site on Coal Creek in September, where 

 the modal category was brackish-fresh (900-1800 mg/L dissolved solids). Elevated dissolved 

 solids at this site were also indicated by a large number of salt-tolerant diatoms in the species 

 Diatoma moniliformis (Table 5). 



The modal category for nitrogen uptake at most of the sites was of nitrogen autotrophic 

 taxa that tolerate elevated concentrations of organically bound nitrogen (Van Dam et al. 1994). 

 At the upper site on Coal Creek the modal category was also of nitrogen autotrophs, but those 

 that tolerate only very small concentrations of organically bound nitrogen (Table 5). Most sites 

 had fairly high or continuously high requirements for dissolved oxygen, but the modal category 

 at four sites was only moderate: Coal Creek at mouth (September), upper Indian Creek, Mormon 

 Creek, and North Fork Greenhorn Creek. A "moderate" rating is equivalent to 50% saturation 

 by dissolved oxygen, whereas fairly high and continuously high ratings are equivalent to 75% 

 and 100% saturation, respectively (Van Dam et al. 1994). 



Beta-mesosaprobous was the modal category for saprobity at most sites. This indicates 

 water that is relatively free of organic matter, oxygen saturation levels ranging from 70-85%, and 

 BOD concentrations ranging from 2-4 milligrams per liter (Van Dam et al. 1994). The modal 

 category at two sites was alpha-mesosaprobous, which indicates elevated organic matter, 25-70% 

 oxygen saturation, and BOD concentrations ranging from 4-13 mg/L. These two sites—lower 

 Coal Creek (September) and lower Ramshorn Creek — also had the lowest pollution index values 

 (Table 4). 



Except for two sites where the modal category for trophic status was "not classified", all 

 of the sites supported mostly eutraphentic diatoms or diatoms that tolerate a wide range of 



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