The surface geology of the upper Boulder River drainage is a 

 complex of metamorphic rocks derived from igneous and sedimentary 

 parent rocks. Bands of shale and limestone outcrop along the 

 base of the mountains near where the river leaves the canyon 

 (Taylor and Ashley, undated) . Limestone outcrops are conspicuous 

 at the Natural Bridge site (Christian Levine, MDEQ, pers . comm. ) . 



Prior to 1999, 24 periphyton samples had been collected from 

 8 sites on the main Boulder River (Table 1) . Two samples were 

 collected near the mouth of the river in the 1970s. Until 1999, 

 chese were the only samples collected from the lower reach of the 

 river. Most of the pre-1999 samples were collected from the 

 upper 4 sites, which have served as least -impaired reference 

 sites for the development of statewide biocriteria for the Rocky 

 Mountain Ecoregions (Bahls et al . 1992) . 



The remaining 5 samples were collected in 1991-1993 from 3 

 sites near the lower end of the upper reach. This is the segment 

 of the river that has generated most of the complaints about 

 excessive algae growth. These 5 samples plus 2 samples collected 

 concurrently from the reference site below the East Fork, are the 

 subject of this report. Levine (1996) describes the physical 

 habitat and river substrates at or near these sampling sites. 



METHODS 



Periphyton samples were collected following standard 

 operating procedures of the MDEQ Planning, Prevention, and 

 Assistance Division. Using appropriate tools, microalgae were 

 scraped, brushed, or sucked from natural substrates in proportion 

 to the rank of those substrates at the study site. Macroalgae 

 were picked by hand in proportion to their abundance at the site. 

 All collections of microalgae and macroalgae were pooled into a 

 common sample container and preserved with Lugol's solution. 



