SUMMARY 



Composite periphyton samples were collected from natural 

 substrates at four sites on the Redwater River near Circle, 

 Montana. Samples were collected following standard operating 

 procedures of the Montana Department of Environmental Quality, 

 processed and analyzed using standard methods for. periphyton, and 

 evaluated following modified USEPA rapid bioassessment protocols 

 for wadeable streams. 



A large siltation index for a prairie stream and an 

 unusually large number of deformed diatom cells indicated 

 moderate impairment, fair biological integrity, and partial 

 support of aquatic life uses at the site (RW-3) immediately below 

 the Circle wastewater lagoons, confirming the assessment made at 

 this site in May 1999. The likely cause of the deformed cells 

 was ammonia. 



Several indicators point to increased organic nitrogen 

 loading from above to below the Circle lagoons: (1) a decrease 

 in nitrogen-fixing cyanobacteria; (2) an increase in Euglena (a 

 pollution tolerant alga) ; (3) a decrease in the diatom pollution 

 index; and (4) a decrease in the percentage of diatoms in the 

 family Epithemiaceae . The diatom flora below the Circle lagoons 

 was quite different from the floras at adjacent stations. 



Although deformed diatoms were also observed at the other 

 sites on the Redwater River, they accounted for less than half 

 the percentage of deformed cells observed below the Circle 

 lagoons . With decreased flows in summer and decompositon of 

 algae and aquatic macrophytes, some of the abnormalities observed 

 in the Redwater River may have been caused by ammonia generated 

 from internal organic loading. The percentage of deformed cells 

 at three of the four stations (1.56% to 1.73%) may be within the 

 normal range for prairie streams in late summer. 



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