Summary 



In August 2003, periphyton samples were collected from two sites on Chicago Gulch, a 

 tributary of Chicago Gulch, and three sites on Collar Gulch in the Judith Mountains at the head 

 of Box Elder Creek in central 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. 



Diatom metrics indicate severe impairment by heavy metals, poor biological integrity, 

 and non-support of aquatic life uses at the upper site on Chicago Gulch and the lower two sites 

 on Collar Gulch. These sites supported diatom assemblages dominated by a single species, had 

 depressed diatom species richness and diversity values, and generated large numbers of 

 physically deformed (teratological) diatom cells. Hormidiiim (= Klebsormidium), a filamentous 

 green alga that can tolerate acid waters contaminated by high concentrations of heavy metals, 

 was present at all three of these sites. 



The upper site on Collar Gulch was severely stressed by acid waters, but there is no direct 

 biological evidence of toxic metals at this site. This site supported a unique diatom assemblage 

 that indicates water with very low pH values and low concentrations of dissolved solids, organic 

 nutrients and inorganic nutrients. 



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A large percentage of motile diatoms indicates moderate to severe impairment from 

 sedimentation in the tributary of Chicago Gulch. This site and the two sites on Chicago Gulch 

 had depressed pollution index values that suggest minor impairment from organic loading. The 

 lower site on Chicago Gulch was the only one of the six sites to fully support aquatic life uses. 

 However, diatom species indicate a sandy and perhaps unstable substrate at this site, and a small 

 percentage of abnormal cells indicate probable chronic metals toxicity. 



