52 Interrelationships of Fishes and Lake Habitats 



from about 2 ppm to 4 or 6 ppm. The water was allowed to run into 

 Pasinski's Pond (3.75 acres) through holes cut in the ice/^ and, over a 

 number of days, opened a hole in the pond 8 to 10 feet in diameter. 

 However, this pumping of aerated well water proved almost useless for 

 preventing the death of fish, because the dissolution of oxygen was not 

 ejBBcient. 



4. Snow Removal. Manual removal of snow from hatchery ponds, 

 although frequently impractical, has caused improvement in dissolved 

 oxygen under ice. Furthermore, pumps and other equipment may be 

 employed. At Green Lake ( Michigan ) water was pumped onto the surface 

 of the ice, and melted the snow to slush for a one-acre area. There was 

 an increase in the amount of dissolved oxygen in water under the ice, 

 even though the slush rapidly became frozen. ^^ 



5. Lamp Black. Tliis substance, spread on snow-covered ice from the 

 air, melted the snow (through absorption of heat) and thereby allowed 

 light penetration which resulted in improved oxygen conditions under 

 the ice.-^ 



6. Circulation of Bottom Water. A perforated plastic hose with small 

 holes at spaced intervals was weighted and laid on the lake bottom to 

 follow the long axis of the lake. The hose was closed at the distal end 

 and attached to an air compressor at the proximal end. The compressor 

 pumped air into the hose so that it bubbled out through the small holes 

 along the entire length of the hose. These jets of air passing from the 

 lake bottom to the surface of the water set up currents of water which 

 eventually carried bottom water at about 39°F to the surface.^^ This 

 warmer water eventually melted the ice and kept a strip of open water 

 above the hose as long as the air compressor was operated, even though 

 the air temperature was close to 0°F. When this system was operated at 

 intervals in a lake subject to winterkill of fishes, no loss of fishes occurred. 



This method has been used to keep open water for ducks, and to 

 prevent ice damage to piers, docks, and other installations. It may be the 

 most successful technique yet devised for preventing winterkill,^- -^'^^'^^-^^ 

 but Patriarche -^ demonstrated that in some lakes the circulation of 

 water having a high biological oxygen demand increased the danger 

 of winterkill. 



An increase in the oxygen supply of water covered by ice can come 

 about only through photosynthesis. Thus, the maintenance of an adequate 

 oxygen supply is dependent upon the presence and activity of green plant 

 life, largely of the plankton algae, and this, in turn, depends upon the 

 transmission of light for photosynthesis. It is conceivable that most of 

 these algae might die or go into dormant stages if forced to remain in 

 darkness (ice covered by snow) for an extended period, so that when 

 sufiicient light for photosynthesis became available again, too few phyto- 



