Diatoms (Tabic 4) 



Nine of the major diatom species in Chicago Gulch and Collar Gulch are sensitive to 

 organic pollution and these were abundant at all six sites (Table 4). Six of the major species are 



somewhat tolerant of organic pollution and these were abundant at all three sites on Chicago 

 Gulch and at the lower site on Collar Gulch. -h 



Chicago Gulch. A large percentage of motile diatoms suggest that the unnamed 

 tributary of Chicago Gulch is moderately to severely impaired by sedimentation (Table 4). 

 These motile diatoms are primarily species of Navicula and Nitzschia. A depressed pollution 

 index also indicates minor impairment from organic loading at this site. Otherwise, diatom 

 diversity, species richness, and equitability were excellent and no abnormal diatom cells were 

 counted at this site. 



The dominant diatom species at the upper site on Chicago Gulch was Synedra rumpens. 

 This species prefers pH values around 7.00 and is known to tolerate elevated concentrations of 

 heavy metals. Over 19% of the diatom cells at this site (27% of the Synedra rumpens cells) were 

 abnormal, which suggests severe impairment by toxic metals. Eunotia exigua was another 

 common diatom here (4.21% abundance). This diatom is classified as acidobiontic, meaning it 

 achieves maximum growth at pH values less than 5.5 (Van Dam et al. 1994). This site had 

 depressed species richness, species diversity, and pollution index values, which indicate at least 

 minor impairment. The middle site shared only about 27% of its diatom assemblage with the 

 tributary site, suggesting that a moderate change in environmental conditions occurred between 

 the two sites. 



Diatom metrics at the lower site on Chicago Gulch indicate significant recovery and only 

 minor impairment from heavy metals and organic loading. The dominant diatom species here 

 were species oi Planothidium, which are adapted to living attached to sand grains. From this, 

 one may conclude that sand is the predominant substrate at this site. Another common species 

 here was Melosira varians, an indicator of elevated concentrations of inorganic nutrients. This 

 site shared only about a quarter of its diatom assemblage with the middle site upstream, which 

 indicates a moderate to major change (improvement) in environmental conditions. 



