light, cold temperatures, low nutrients) can mimic the effects of 

 man-caused impairment on these metrics. An experienced 

 phycologist with some knowledge of the study stream can usually 

 sort out the natural stressors from the man-made ones. 



The criteria in Table 3 distinguish among four levels of 

 impairment and three levels of aquatic life use support: no 

 impairment or only minor impairment (full support); moderate 

 impairment (partial support); and severe impairment (nonsupport) . 

 These impairment levels correspond to excellent, good, fair, and 

 poor biological integrity, respectively. 



Only periphyton samples collected in summer (June 21- 

 September 21) can be compared to reference stream samples because 

 metric values change seasonally and summer is the season in which 

 reference streams were sampled for biocriteria development. The 

 similarity index, which measures the degree of floristic affinity 

 between a study site and an upstream control site, may be used at 

 any time of the year. The similarity index may also be used to 

 guage the relative amount of impairment or recovery that occurs 

 between adjacent study sites (Table 3) . 



RESULTS AND DISCUSSION 



Results are presented in Tables 4 and 5, located near the 

 end of this report following the Literature Cited section. In 

 each table, stations and their associated data are listed in 

 order from upstream to downstream (left to right) . Completed 

 diatom proportional count forms are attached as Appendix A. 



NON-DIATOM (SOFT) ALGAE 



Upper Big Spring Creek had a relatively simple algal flora 

 consisting of diatoms and Phormidium, a filamentous blue-green 



