biotic stream responses to stream reaeration 47 



Conclusions 



The pertinent data on stream condition are diagrammatically summar- 

 ized in Figure 5. Without question, there are definite biotic responses to 

 industrial pollution and the environmental conditions that result. Decreases 

 in population of bacteria and plankton and abrupt loss in variety of bottom 

 organisms below the industrial sewer suggest the presence of a toxic ingredi- 

 ent. Gas production and the rising of bottom fiber mats occur in the 

 region of oxygen depression. This region is unsuitable for many kinds of 

 organisms, but the persistent ones thrive, and scavengers are numerous. 



ficiol HMtrotioA 



Fig. 6. Stream zones, north fork of Flambeau river. 



Abrupt improvement of the biological picture below the site of arti- 

 ficial reaeration was not apparent. At the same time, improvement in 

 the recovery zone may be accelerated so that a normal, clean water biota 

 extends farther upstream. 



The available data show that conditions for biotic existence below the 

 20 mile level are similar to those above Park Falls. These are the zones 

 of clean water as shown in Figure 6. Thirteen miles of stream are seri- 

 ously affected by pollution and have little recreational or other value. For 

 2.5 miles below Park Falls, in the zone of degradation, dissolved oxygen 

 decreases to 40 per cent saturation and inhibitory substances are present. 

 Below this zone oxygen conditions are poorest for aquatic life. Dissolved 



