Summary 



In July 2003, periphyton samples were collected from three sites on Beaver Creek in the 

 Big Spring Creek TMDL planning area in central Montana to assess whether this stream is 

 water-quality limited and in need of TMDLs. The Beaver Creek 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. 



Samples of conspicuous macroscopic algae were also collected from Casino Creek and 

 Cottonwood Creek in July 2003 to identify the taxa responsible for these growths. Results are 

 reported here and in a memo dated October 9, 2003. These samples were not collected following 

 MDEQ standard operating procedures. 



The upper site on Beaver Creek was moderately impaired by sedimentation and 

 provided less than full support for aquatic life uses. The pollution index was depressed at the 

 upper site, suggesting minor impairment from organic loading. The lower site was also 

 moderately impaired by sedimentation, but the pollution index here was just above the threshold 

 for minor impairment. The middle site had the best biological integrity of the three sites on 

 Beaver Creek. Diatom metrics indicate only minor disturbance and minor impairment from 

 sedimentation here. The eutraphentic diatom Gomphonema minutum was a dominant species at 

 both the middle and lower sites, indicating elevated concentrations of inorganic nutrients at both 

 sites. The green alga Cladophora ranked second in biomass at these two sites. 



The algal specimen collected from Casino Creek was a large colony o^ Cladophora, 

 probably Cladophora glomerala. Cladophora is a common mat-forming filamentous green alga 

 that often becomes a nuisance in nutrient-rich waters around the world. The bright green color 

 indicates fresh new growth, that is, epiphytic diatoms had not yet had a chance to colonize the 



filaments. 



The algal specimen collected from Cottonwood Creek proved to be a colony of diatom 

 cells embedded in amorphous mucilage. The cells were mainly a Cymbella species and a 

 Synedra species. These taxa are known to extrude polysaccharide mucilage through pores in 

 their cell walls, thus forming stalks, tubes, and amorphous masses in which the diatoms live. 

 Certain species of Cymbella and Synedra are associated with eutrophication. 



