SUMMARY 



In August 2001, composite periphyton samples were collected 

 from 6 sites on the Tongue River in southeastern Montana for the 

 purpose of assessing whether this stream is water-quality limited 

 and in need of TMDLs and to evaluate the biological effects of 

 salty groundwater being discharged from coal-bed methane wells. 

 The samples were collected following DEQ standard operating 

 procedures, processed and analyzed using standard methods for 

 periphyton, and evaluated following modified USEPA rapid 

 bioassessment protocols for wadeable streams. 



Despite continued drought and record low flows in 2001, the 

 algal flora of the Tongue River indicated cool, fresh waters and 

 good to excellent biological integrity at most sites, with no 

 overt effects of salinization in evidence. 



Sedimentation was the most serious problem in the Tongue 

 River as indicated by diatom metrics. A large percentage of 

 motile diatoms indicated moderate impairment from sediment and 

 partial support of aquatic life uses at TR05 . Little or no 

 impairment from sedimentation was noted at the other sites. 



Due to the flow- and temperature-stabilizing effects of 

 reservoir releases, the attached filamentous green alga 

 Cladophora dominated below Tongue River Dam. A large number of 

 Cocconeis pediculus, a common epiphyte on Cladophora, indicated 

 moderate impairment and partial support of aquatic life uses at 

 TR03 due to habitat homogeneity. Minimum values for diatom 

 diversity and species richness were also recorded below the dam. 



A large percentage of nitrogen- fixing diatoms indicated 

 nitrogen-poor conditions immmediately below Tongue River Dam. 

 Sites above and below Tongue River Reservoir were very different, 

 f loristically . A small number of teratological diatom cells- - 

 cause unknown- -was observed at each of the four upstream sites. 



