Summary 



In August 2002, periph>ton samples were collected from 2 sites on Sullivan Creek and 1 

 site on Skyland Creek in the upper Flathead River TMDL planning area in northwestern 

 Montana for the purpose of assessing whether these streams are water-quality limited and in need 

 of TMDLs. The samples were collected following MDEQ standard operating procedures, 

 processed and analyzed using standard methods for periphyton, and evaluated following 

 modified USEPA rapid bioassessment protocols for wadeable streams. 



Hvdnints foetidus was the most abundant alga at all three sites. This cold-water 

 stenotherm thrives in flashy mountain streams that have unstable channels and exhibit wide 

 seasonal fluctuations in flow, temperature, and turbidity. H. foetidus, a chrysophyte, grows best 

 in full sunlight and achieves maximum standing crop in winter and spring when flows are stable 

 and turbidity is low. 



Sullivan Creek above Connor Creek was subject to major environmental stresses that 

 were natural in origin. The cold-water stenotherm and pollution-sensitive diatom Hannaea arcus 

 accounted for over 80% of the diatom assemblage at this site. Although diatom species richness, 

 equitability, and diversity were very low, values for the pollution index, sedimentation index, 

 and percent abnormal cells indicated excellent water quality at this site. The stresses detected 

 here were probably due to cold temperatures, low nutrient concentrations, steep gradients, and/or 

 fast current velocities. 



A significant increase in organic loading was detected at the site on Sullivan Creek 

 below Quintonkon Creek, resulting in minor impairment. The dominant diatom species here 

 was FragUaria vaucheriae, a species that is somewhat tolerant of organic pollution. Modal 

 categories for diatom ecological attributes indicate reduced availability of dissolved oxygen at 

 this site and an increase in both organic and inorganic nutrients. 



Diatom metrics indicate even greater organic loading in Skyland Creek above Bear 

 Creek, resulting in moderate impairment. Encyonema silesiacum, a pollution-tolerant diatom, 

 accounted for over half the diatom cells counted at this site. Most diatoms here exert only a 

 moderate demand for dissolved oxygen, as compared to a continuously high demand at the two 

 sites on Sullivan Creek. The modal category for saprobity at the Skyland Creek site was alpha- 

 mesosaprobous, which is the same modal category as the lower site on Sullivan Creek and 

 indicates waters with 25-70% oxygen saturation and 4-13 mg/L BOD. 



