Nostoc was the most abundant alga at the upstream site 

 (WardC-01) . Nostoc, like other cyanobacteria, is capable of 

 fixing molecular (atmospheric) nitrogen and is not dependent on 

 nitrogen dissolved in the water. Its abundance at station 01 

 indicates cool, flowing waters that are relatively poor in 

 nitrogen. Nostoc disappeared at the downstream site. 



Diatoms ranked first in biovolume at the downstream site, 

 followed by two genera of filamentous green algae: Cladophora and 

 Ulothrix. The increase in the number of genera and the increase 

 in biovolume of filamentous green algae from station 01 to 02 

 indicates an increase in nutrient concentrations between these 

 sites. This increase in nutrients is probably accompanied by an 

 increase in water temperature and a slowing of current velocity. 



Cladophora, which was absent at 01 but frequent at 02, is a 

 widespread alga that often becomes a nuisance in waters that are 

 enriched with nutrients. Stigeoclonium, which was also absent at 

 01 but common at 02 (Table 5) , is a reliable indicator of organic 

 enrichment (Palmer 1969) . Ulothrix , which is somewhat less 

 tolerant of pollution than Stigeoclonium, was frequent at 02 but 

 also absent at 01 (Table 5) . Oscillatoria, which ranks as the 

 second most pollution- tolerant genus of freshwater algae (Palmer 

 1969), increased in abundance from occasional at station 01 to 

 frequent at station 02. 



The presence of the chrysophyte Vaucheria at station 02 

 indicates stable flows of cool waters at this site. Vaucheria is 

 a common alga in springs and spring streams. 



DIATOMS 



Although most of the major diatom species in Ward Creek are 

 sensitive to organic pollution, three species of Navicula are 

 somewhat tolerant of pollution (pollution class 2) . All three of 



8 



