hatchery operations 1 1 1 



Table 15. amounts of oxygen added to pond waters by different tech- 

 niques OF emergency aeration. (SOURCE: BOYD 1979.) 



OXYGEN RELATIVE 



ADDED EFFICIENCY 



TYPE OF EMERGENCY AREATION (LB/ACRE) ("..) 



Paddlewheel aerator 48.9 100 



Crisafulli pump with sprayer 31.2 64 



Crisafulli pump to discharge oxy- 19.0 39 



genated water from adjacent 



pond 

 Otterbine aerator (3.7 kilowatts) 15.2 31 



CrisfuUi pump to circulate pond 11.8 24 



water 

 Otterbine aerator (2.2 kilowatts) 11.3 23 



Rainmaster pump to circulate 10.7 22 



pond water 

 Rainmaster pump to discharge 6.0 12 



oxygenated water from adjacent 



pond 

 Air-o-later aerator (0.25 kilowatt) 3.9 8 



(CO3") or hydroxyl (OH ), that react with H^ and reduce the latter's con- 

 centration. 



Excessively high pH values can occur in ponds during summer, when 

 phytoplankton are abundant and photosynthesis is intense. As carbon diox- 

 ide is added to ponds, either by diffusion from the atmosphere or from 

 respiration, it reacts with water to form a weak carbonic acid. The basic 

 reaction involved is: 



CO^ + H^O ^ H^C03 ^ H+ + HCOr ^ 2H+ + C03=. 



As more CO2 is added, the reaction moves farther to the right, generating 

 first bicarbonate and then carbonate ions; H"*^ is released at each step, 

 increasing the acidity and lowering the pH. Photosynthesizing plants 

 reverse the reaction. They take CO2 from the water, and the HC03~ and 

 CO3" ions bind hydrogen; acidity is reduced and pH rises — often to levels 



above ten. 



Two types of treatment for high pH can be applied. One involves addi- 

 tion of chemicals that form weak acids by reacting with water to release 

 H^; they function much like CO^ in this regard. Examples are sulfur, fer- 

 rous sulfate, and aluminum sulfate, materials also used to acidify soils. The 

 action of sulfur is enhanced if it is added together with organic matter, 

 such as manure. 



A second treatment for high pH is the addition of positively charged 

 ions that bind preferentially with COa^; they keep the carbonate from 



