produces ear-shaped colonies after being occupied by aquatic midge larvae. The filamentous 

 green alga Zygnema was frequent and ranked third in biovolume in the Deer Creek sample. 

 Zygnema is widespread and prefers neutral to slightly acidic waters. 



Overwhich Creek. Besides diatoms, which were abundant in both samples, Oscillatoria 

 dominated the periphyton community at both sites on Overwhich Creek. (See discussion of 

 Oscillatoria under Deer Creek.) The green alga Gongrosira was frequent and ranked third in 

 biovolume at the upper site. Gongrosira forms crusts on hard surfaces and prefers alkaline 

 waters. The nitrogen-fixer Nostoc was frequent and ranked third at the lower site. The attached 

 filamentous green alga Ulothrix was common and ranked fourth at both sites. Ulothrix grows 

 attached to rocks in streams with slow to moderate currents and generally prefers cool waters. 



Buck Creek. The coenocytic filamentous Vaucheria (Tribophyceae) was abundant and 

 ranked first in biovolume in the sample from Buck Creek. Vaucheria typically grows on muddy 

 bottoms and prefers cool waters of low to medium nutrient content. It is sensitive to desiccation 

 so its presence is usually an indicator of constant flows and the absence of dewatering. Other 

 algae, including diatoms, were rare to occasional in the sample from Buck Creek. 



Nez Perce Fork. Diatoms were most abundant and ranked first in biovolume in 

 samples from the upper and middle sites on Nez Perce Fork. Nostoc was frequent and ranked 

 second at the upper site, followed by the desmid Closterium (common) and the xanthophyte 

 Tribonema (occasional). Closterium includes many widespread species that are found in a wide 

 variety of habitats. The ecology of Tribonema is similar to that of Vaucheria in that it prefers 

 cool waters of low to medium nutrient content. 



At the middle site, the second-, third- and fourth-ranked genera were Oscillatoria, 

 Audouinella, and Spirogyra, respectively. Audouinella is a filamentous red alga. Audouinella 

 hermainnii, the most common species in North America, prefers cool (~11°C), mildly alkaline 

 (pH -7.5) waters of low ionic content (-100 uS). 



