streams of North America. The gelatinous envelope in which the cells are embedded is 

 exceedingly tough and the plant frequently covers the entire surface of submerged rocks 

 and has caused more than one hiker to lose his or her footing when crossing a stream. It 

 normally begins to disappear when water temperatures rise much above 1 0°C . . . Other 

 requirements for this species apparently include low pH and bright sunlight. 



The nitrogen-fixing cyanophyte Tolypothrix was frequent at the lower site and ranked 5"^, 

 followed by the branched filamentous green alga Stigeoclonium, which was also frequent. 

 Stigeoclonium is tolerant of organic pollution and its presence may indicate an increase in 

 organic loading at this site. 



Diatoms (Table 4) 



All of the major diatom species from Hughes Creek are included in pollution tolerance 

 classes 3 or 2, and are either sensitive to organic pollution or only somewhat tolerant of organic 

 pollution (Table 4). 



Diatom metrics for both sites on Hughes Creek indicate excellent biological 

 integrity, no impairment, and full support of aquatic life uses (Table 4). However, pollution 

 index values at both sites (2.53 and 2.54) approached the threshold for minor impairment in a 

 mountain stream (2.50). This slight organic loading may be natural in origin and due to an 

 accumulation of terrestrial plant debris and/or algae. Several of the major diatom species (e.g., 

 Diatoma mesodon, Fragilaria spp., Hannaea arcus, Staurosira construens, Synedra spp.) are 

 free-living and indicate a history of stable flows at these sites and the absence of recent bottom- 

 scouring events. These diatoms also indicate cold waters. 



Although sedimentation index values did not exceed the threshold for minor impairment 

 at either site, a large amount of fine sand was noted in the sample collected at the lower site (see 

 sample notes, above). This site also had the larger sedimentation index value of the two sites 

 based on the percentage of mofile diatoms that were counted. In addition to motile diatoms, 

 these sites supported large numbers o{ Planothidium lanceolatum, a diatom species that is 

 adapted to living attached to grains of sand. If the percentage of Planothidium lanceolatum at 



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