48 LIMNOLOGY, WATER SUPPLY AND WASTE DISPOSAL 



oxygen approaches or reaches zero in the zone of active decomposition and 

 then slowly climbs to a level sufficient for a variety of organisms. Improve- 

 ment continues in the recovery zone with normal biotic populations at the 

 20-mile level. 



Biotic responses to stream pollution lead to the intense biochemical 

 activities that assist in sanitary recovery. Bad as it may seem, localized 

 stream defilement is a necessary part of the process. Only by this sacrifice 

 are the recreational downstream areas preserved. 



SUMMAEY 



During the summer months, since 1944, diffused air has been pumped 

 into the North Fork of the Flambeau River near Park Falls, Wisconsin, 

 in an attempt to alleviate the serious conditions resulting from sulphite 

 pulp and paper mill pollution. While four years of study have shown bene- 

 fits from the artificial reaeration procedure, biotic responses to pollution 

 under these conditions were unknown. 



Investigation has shown no abrupt biological improvement near the 

 artificial reaeration site, but improvement in the downstream recovery 

 zone is accelerated. The introduction of these industrial pollutants has an 

 immediate toxic influence upon most organisms and alters the biological 

 picture for a distance of 20 stream miles. In this region the societies of 

 organisms increase, reach a population peak, and decrease in linear order 

 as their biochemical activities change the degree and character of pollu- 

 tion. Action upon the pollutants in the 20-mile zone produces local critical 

 conditions but, in so doing, protects downstream recreational areas. 



