For saprobity (BOD loading), the modal category for most sites was "unclassified" or the 

 typical '"beta-mesosaprobous". Exceptions were "alpha-mesosaprobous" at the lower site on 

 Chicago Gulch and "oligosaprobous" at the upper site on Collar Gulch. "Alpha-mesosaprobous" 

 indicates a larger than typical level of organic loading than most mountain streams and is 

 equivalent to 25-70% dissolved oxygen saturation and a BOD5 value of 4-13 mg/L (Van Dam et 

 al. 1994). "Oligosaprobous" represents a smaller than typical level of organic loading and is 

 equivalent to >85% dissolved oxygen saturation and a BOD5 value of <2 mg/L. 



Most diatoms at the tributary' and lower sites on Chicago Gulch belong to the guild of 

 eutraphentic diatoms. These diatoms indicate larger concentrations of inorganic nutrients (C, N, 

 P) than the other sites. The modal categor>' for trophic state at the upper site on Collar Gulch 

 was "variable". Diatoms in this group can tolerate a wide range of trophic conditions ranging 

 from oligotrophic to eutrophic. The modal category was "oligo-mesotraphentic" at the 

 remaining three sites. Diatoms in this category can live on small concentrations of inorganic 

 nutrients, which may be tied up in metallic precipitates and made inaccessible for algal growth. 



References 



APHA. 1998. Standard Methods for the Examination of Water and Wastewater. 20 Edition. American Public 

 Health Association, Washmgton, D.C. 



Bahls, L.L. 1979. Benthic diatom diversity as a measure of water quality. Proceedings of the Montana 

 Academy of Sciences 38:1-6. 



Bahls, L.L. 1993. Periphyton Bioassessment Methods for Montana Streams (revised). Montana Department of 

 Health and Environmental Sciences, Helena. 



Bahls, L.L. , Bob Bukantis, and Steve Tralles. 1992. Benchmark Biology of Montana Reference Streams. Montana 



Department of Health and Environmental Sciences, Helena. 



Barbour, M.T., J. Gemtsen. B.D. Snyder, and J.B. Stribling. 1999. Rapid Bioassessment Protocols for Use 

 In Streams and Wadeable Rivers; Periphyton, Benthic Macroinvertebrates and Fish. Second Edition. 

 EPA'841-B-99-002. U.S. Environmental Protection Agency, Office of Water, Washington, D.C. 



Beaver, Janet. 1981. Apparent Ecological Characteristics of Some Common Freshwater Diatoms. 

 Ontario Ministry of The Environment, Technical Support Section, Don Mills, Ontario. 



Johansen, J.R. 1999. Diatoms of Aerial Habitats. Chapter 12 in Stoermer, E.F., and J. P. Smol (eds.), The Diatoms: 

 Applications For the Environmental and Earth Sciences, Cambndge University Press, New York. 



11 



