v.. 



SUMMARY 



In early August 1999, composite periphyton samples were 

 collected from natural substrates at 8 sites on Box Elder Creek 

 in central Montana. 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. 



Box Elder Creek is an intermittent "pooled channel" stream 

 with a silty bottom. It is classified C-3 in the Montana Surface 

 Water Quality Standards. 



Box Elder Creek supported a very diverse algal flora. The 

 non-diatom algae indicated warm, standing waters with elevated 

 concentrations of organic nutrients . This organic loading was 

 probably internal and natural in origin (i.e., from decaying 

 aquatic vegetation) . Nitrogen was likely the limiting nutrient 

 in Box Elder Creek, especially in the middle and lower reaches of 

 the study section. In reaches 003 and 004, the presence of Chara 

 indicated stable soft substrates and low levels of turbidity. 



The diatom assemblages of Box Elder Creek supported the 

 findings of organic nutrient loading and nitrogen limiting 

 conditions, the latter particularly in the lower reaches of the 

 study section. Diatom metrics also indicated low levels of 

 disturbance and elevated concentrations of dissolved solids. 



The relatively large percentage of motile diatoms indicated 

 moderate levels of sedimentation in all reaches except Reach 001. 

 Moderate impairment was indicated even in the reference reach 

 (Reach 022) , which was judged to be "proper functioning" based on 

 the good condition of the riparian habitat. This may indicate 

 that the sedimentation index is more responsive to channel 

 morphology and stream type than it is to riparian condition. 



• 



