Summary 



In August 2002, pcriph>'ton samples were collected from Jackson Creek, Jennies Fork, 

 and Granite Creek in the Lake Helena TMDL planning area in west central Montana for the 

 purpose of assessing whether these streams are water-quality lim.ited 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. 



A large number of motile diatoms in Jackson Creek indicate moderate impairment 



from sedimentation and only partial support of aquatic life uses. The pollution-tolerant blue- 

 green alga Oscillatoria was abundant and ranked first in biovolume in Jackson Creek. The 

 pollution index here indicated minor impairment and somewhat elevated organic loading for a 

 mountain stream. In addition, a larger than norma! number of teratological diatom cells may 

 indicate chronic toxicity from elevated heavy metals at this site. 



Hydrurus foetidus was the most abundant alga in Jennies Fork. This cold-water 

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

 seasonal fluctuations in flow, temperature, and turbidity. A large number of Achnanthidium 

 minutissimiim in Jennies Fork indicates minor stress from natural scour. The pollution index and 

 the sedimentation index indicate minor impairment from organic loading and sedimentation, 

 respectively. Four teratological diatom cells were recorded at this site, which may indicate low 

 background levels of heavy metals. 



Granite Creek had the best biological integrity of the three sites, although both the 

 pollution index and the sedimentation index approached their respective thresholds for minor 

 impairment. The filamentous green alga Cladophora was abundant in Granite Creek. Streams 

 that support large stands of filamentous algae typically have more stable flows, firmer substrates, 

 and larger concentrations of inorganic nutrients than streams that do not support these algae. The 

 presence ofNostoc in Granite Creek indicates that nitrogen was likely the limiting nutrient at this 

 site. Unlike Jackson Creek and Jennies Fork, where most diatoms require continuously high 

 levels of dissolved oxygen and tolerate variable concentrations of inorganic nutrients, most 

 diatoms in Granite Creek require only moderate levels of dissolved oxygen and indicate 

 eutrophic conditions. 



