Lake Size and Productivity 39 



yields and varying amounts of ionized hydrogen, carbon dioxide, or 

 chlorides. Further, there was no relationship between sulfates and pro- 

 duction until the sulfates exceeded 300 ppm.-^ Table 2.1 shows a 

 productivity classification of natural lakes (Minnesota) on tlie basis of 

 total alkalinity and sulfate ions.-*^ 



Table 2.1 A classification of natural lakes in Minnesota on the basis 

 OF total alkalinity and sulfate ions (from moyle-0). 



Minnesota ponds containing amounts of phosphorus below 0.05 ppm 

 had low fish yields.^*^ Above a concentration of total phosphorus of 0.05 

 ppm, there was little difference in either average or maximum yield. Moyle 

 concluded that the optimum concentration of total phosphorus might lie 

 between 0.1 and 0.2 ppm; however, these phosphorus concentrations were 

 usually associated with heavy algal blooms which may create a danger 

 through their ability to cause sudden oxygen depletion. 



LAKE SIZE AND PRODUCTIVITY 



Prior to 1946, there seemed to be evidence of a straight-line negative 

 logarithmic relationship between size of a lake and fish production, when 

 all data then available were used.-^ These data included complete fish 

 censuses of a number of small ponds, creel censuses as measurements of 

 production on medium-sized waters, and commercial catches of fish on 

 the larger lakes. No consideration was given to the possible effect of the 

 geographical location of these waters and of regional soil fertility on 

 production. 



Later, when these data were reworked and consideration was given to 

 location and soil fertility, the apparent relationship between size and 

 productivity disappeared.^ Information on yields from additional lakes 

 (Minnesota) -^ in the form of average gill net ratios demonstrated that 

 lakes of over 5000 acres in area were more productive than those of 

 smaller sizes, while data from creel censuses indicated that lakes ranging 

 in size between 500 and 1000 acres were more productive than those 



