Nitzschia galea is on- vera! diatom species that thrives on 

 organic nitrogen compounds (11). .i. .Dundance at itatic, VIII is 

 apparently in response to the a load introduced by the Yegen 



Drain (Tables II and III). The c - N. palea to deaminate amino 

 acids and liberate free ammonia to t ,. . ;.„. ..aj .^ in part re- 

 sponsible for the rapid reduction in all nitrogen species below Yegen 

 Drain and the eventual recovery to near baseline levels at Huntley (IX). 

 With four times the nitrogen load, it is not clear why the Yegen Drain (VII) 

 had only one-third the N. palea p lowstone station 



downstream (VIII). This may be due to : tense competition and/or 

 physical factors less favorable to N, palea in the Yejc L..ain. 



Except for nitrate (Table II), wate at the mouth 

 CI arks Fork River (Station II) appears to b 



relatively low diversity values (Table III). The Clarks For^ "--' 

 discharges through Laurel have no discer ffect on Yellow- 



stone River periphyton at Duck Creek Bridge- ). 



The phytoplankton data from the 19b^ . ■^. ...... ■...,. ^ ..rvey (10) are 



not strictly comparable to the data rep Nevertheless, it 



is evident that water quality has inu considerably in the intervening 

 20 years. On the whole, comparing sa,.f... from Laurel and Huntley, 

 Yellowstone River periphyton was not ed by perturbations 



through Billings in 1975. Self-puri i and recovery of the micro- 

 flora from pollution may be consiu^.^.. _^. .^.-.^ -i Huntley. 



11 



