performed. This division is based on the general contentions that warm- 

 water fishes can tolerate greater population densities and physico-chemical 

 extremes J that warm-water fishes occur in lakes of higher temperature which 

 signify higher metabolic rates and^ perhaps, greater productivity; and thatj 

 Qther things being equal, warm-water fishes respond more readily to fertili- 

 zation. 



Experiments in Lake Fertilization 



Pioneer work in scientific lake enrichment was done by Juday et al. 

 (1938) on a 39 "acre, UU-foot (maximum) depth, seepage lake containing small- 

 mouth black bass and yellow perch. Various fertilizers were added over a 

 5-year period as follows: 1932, superphosphate; 1933> superphosphate and 

 lime; 1931, superphosphate, lime, and ammonium sulfate; 1935^ potassium 

 chloride and cyanamid; 1936, soybean meal. The effects were studied in 

 terms of dissolved ions, plankton quantity, and growth rates of perch. 

 Initially, the water was "very soft" (0.7 parts per million calcium). Added 

 nutrients raised the water levels of phosphorus, nitrate, and calciiom, but 

 only the latter remained above prefertillzation level. Plankton content 

 and perch growth did not chan^^e significantly until after the 1936 fertili- 

 zation, whereupon a sharp increase was noted in both. These biological 

 Indexes continued high the following year and the authors concluded that 

 organic matter was more effective than mineral fertilizers used singly or 

 in groups. Therefore, the organic content of the lake appeared to be 

 limiting. 



King (I9U3) reported the fertilization (6:9;3 and sodium nitrate) of 

 a shallow, acid (pH 5,2 to 7,0), 21-acre lake containing largemouth bass, 

 bluegill, and several types of coarse fish. Productive changes were studied 

 in terms of fishing returns (average catch per hour, average creel weight, 

 and pounds per acre caught) . Comparison of these indexes before and after 

 fertilization showed a decrease in fishing returns, bub the drop was not 

 as great in the fertilized lake as in a nearby control lake. Ball (1950) 

 and Ball and Tanner (1951) fertilized one of two adjacent shallow seepage 

 lakes containing several species of warm-water fish. Inorganic 10; 6:1; was 

 added at 3-week intervals. May to mid-September, at the rate of 100 pounds 

 per acre, in I9U6 and 19U7. Definite plankton gains followed each applica- 

 tion and growth rates of t^me fish showed significant increase. Heavy 

 algal mats, which restricted spawning, formed during the second summer. 

 Neither lake had experienced a winterkill within 10 years before fertiliza- 

 tion, but anaerobic conditions under a winter Icecap caused the destruction 

 of most fish and insect life in the fertilized lake following the second 

 year of nutrient addition. The fertilized lake was restocked in I9U8 and 

 the fish grew rapidly. Filamentous algae presented no further problem, 

 and plankton blooms did not occur in the ensuing summer. Surber (19it8) 

 successfully fertilized a UU-acre recreational lake with 5slO;5 and lime, 

 to control nuisance excesses of submerged aquatic plants o It was also 

 noted that fishing inproved. 



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