i 



w 



its diatom assemblage with the upstream site, indicating that a moderate amount of floristic and 

 environmental change occurred between them. 



Modal Categories 



Several ecological attributes were selected from the diatom reports in the appendix and 

 modal categories of these attributes were extracted to characterize water quality tendencies at the 

 two sites (Table 5). 



Modal categories at both sites indicate alkaline and eutrophic waters with 25 - 70% 

 dissolved oxygen saturation and 4-13 mg/L BOD5. However, other modal categories suggest 

 that the downstream (Hevron Road) site had more unstable substrates (more highly motile 

 diatoms), higher concentrations of dissolved solids (more brackish-fresh diatoms), and higher 

 levels of organic nitrogen (more nitrogen heterotrophs) than the upstream site (Table 5). 



References 



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

 Health Association, Washington, 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. 2003. Biological Integrity of Dog Creek and Eagle Creek Based on the Structure and Composition of 

 the Benthic Algae Community. Prepared for the Montana Department of Environmental Quality by Hannaea, 

 Helena, Montana. 



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



Deparmient of Health and Environmental Sciences, Helena. 



Barbour, M.T., J. Gerritsen, 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/84 l-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. 



