Jim Creek. The diatom association of Jim Creek indicated the lowest amount of stress 

 of any of the sites that were sampled (Table 4). However, Jim Creek also had the lowest 

 pollution index and the highest sedimentation index of any site, indicating that this stream 

 supported larger sediment and organic nutrient loads than any of the other sites. Nevertheless, 

 values for these metrics were still in the range of excellent biological integrity for a mountain 

 stream (Table 2). Jim Creek also supported the largest number of diatom species and the highest 

 diversity of any site. These metrics tend to increase in mountain streams in response to small to 

 moderate increases in sediments and nutrients (unpublished observation). 



Piper Creek. Like Elk Creek, Piper Creek had very low diatom diversity and species 

 richness and very high values for the disturbance index and percent dominant species (Table 4). 

 And like Elk Creek, Achnanthidium minutissimum was the dominant diatom species in Piper 

 Creek, indicating natural stress from cold, fast waters of low nutrient content. Values for the 

 pollution index and sedimentation index indicate very little loading of sediment or organic 

 nutrients in Piper Creek. The two sites on Piper Creek had virtually identical diatom 

 assemblages, indicating little or no perturbation occurred between them. 



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 in the 

 four streams (Table 5). The four tributaries and stations within each tributary are fairly uniform 

 in their general water quality characteristics, which may be described as circumneutral, fresh- 

 brackish (TDS <900 mg/L), and mesotrophic, with continuously high concentrations of dissolved 

 oxygen. Diatoms living in these streams are mostly attached (non-motile), autotrophic with 

 respect to nitrogen, tolerate a wide range of nutrient concentrations, and live mainly in water 

 bodies, but regularly in wet places. They indicate some organic loading, which may be natural, 

 but zones where the oxidation of biodegradable organic matter is mostly complete (Van Dam et 

 al. 1994). 



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;l-6. 



