Summary 



In June of 2003, periphyton samples were collected from 8 sites on East Redwater River, 

 Horse Creek, and Pasture Creek 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. 



A large percentage of highly motile diatoms resulted in moderate impairment from 

 sedimentation and partial support of aquatic life uses at sites 04 and 02 on the East Redwater 

 River and at the upper site on Horse Creek. A very large percentage of motile diatoms resulted 

 in severe impairment and nonsupport of aquatic life uses at the lower site on Horse Creek. 



A large percentage of pollution tolerant diatoms resuhed in moderate impairment from 

 organic loading and partial support of aquatic life uses at the upstream site on the East Redwater 

 River and at both sites on Horse Creek. These sites are also affected by elevated concentrations 

 of dissolved solids (sahnity). 



Large percentages of Rhoicosphenia abbreviata resulted in depressed diatom species 

 richness, diversity, and equitability values at East Redwater River sites 01 and 03 and, to a lesser 

 extent, at Pasture Creek site 01. R. abbreviata prefers cool, flowing, fresh waters with higher 

 levels of dissolved oxygen. In large numbers, it is more typical of mountain streams than of 

 plains streams. Its abundance in these samples may be the result of higher current velocities at 

 these sites, an influx of fresher (less saline) waters, and the relatively early sampling dates. 



Pasture Creek had the best water quality and biological integnty of the three streams. 

 Diatom metrics indicate little or no excess sedimentation and only minor organic loading here. 

 Major diatom species at the upstream site indicate significantly higher salinity levels than the 

 downstream site. The downstream site also supported the largest percentage of Rhopalodiales 

 among samples in the sample set, indicating that nitrogen may be the limiting nutrient here. 



