SUMMARY 



On May 4, 2000, composite periphyton samples were collected 

 from natural substrates at 3 sites on lower Squirrel Creek in 

 southeastern Montana for the purpose of evaluating the biological 

 effects of groundwater being discharged from wells used to test 

 the feasibility of coal-bed methane development. Samples were 

 collected, processed and analyzed following standard methods. 



Upper Squirrel Creek (si«-.e #4) had excellent algal diversity 

 and species richness, indicating a stable and healthy aquatic 

 community. Diatom association metrics at site #4 indicated good 

 to excellent biological integrity and full support of aquatic 

 life uses. Site #4 proved to be a suitable reference site. 



Squirrel Creek at the culvert (site #3) was moderately 

 impaired by siltation and had significantly depressed diatom 

 diversity. Besides siltation, elevated concentrations of organic 

 nutrients and salts were the likely causes of impairment at this 

 site. , The culvert site was significantly different, in terms of 

 diatom species composition and diatom metrics, from the upstream 

 reference site. 



Site #1 near the mouth of Squirrel Creek was also moderately 

 impaired but it had better biological integrity than did site #3. 

 The composition of the diatom associations at sites #1 and #3 

 indicated that site #1 had cooler water temperatures, higher 

 dissolved oxygen concentrations and lower nutrient concentrations 

 than site #3 . Discharges of pumped groundwater between sites #3 

 and #1 did not cause a further decline in biological integrity. 



The two duplicate samples collected from site #1 had 

 essentially identical diatom floras. A comparison of metrics 

 generated from samples collected this year with metrics generated 

 from samples collected in 1978-80 indicated little or no change 

 in biological integrity at this site in the intervening 20 years. 



