calcium. These substances were added to the water in quantities that 

 yielded the most fish„ This approach proved successful in pond culture, 

 consequently„ little consideration was given to the action of these nu- 

 trients or to the many other elements essential to living matter. It 

 was realized some years ago that nitrogen and potassium were not always 

 needed, Davis and Wiebe (1930) presented the European opinion that fer- 

 tilization with nitrogen and potassium is varied in effect, but all agree 

 to the importance of phosphorus. Smith (1932a) found that plankton pro- 

 duction varied directly with nitrogen and phosphorus concentrations,, but 

 irregularities occurred when nitrogen was used alone. Recentlyj Zeller^ 

 concluded that only phosphorus fertilizers need be used in Missouri ponds. 

 While this is far from a complete picture of the work that has been done^ 

 it illustrates the need for a more fundamental approach to the study of 

 chemical enrichment. 



¥iesner (1937) listed 17 elements necessary to formulate and sustain 

 life. Grouped in order of decreasing importance, they are; oxygen, hydro- 

 gen^ carbons nitrogen| sulfur _, phosphorus, sodium, potassium^ calcium, 

 magnesium, iron, chlorine, fluorine^ silicon, manganese, iodine, and arsenic, 

 Most of these appear in the environment as compounds of two or more elements- 

 Optimum ranges of some compounds have been established for certain organ- 

 isms. Moyle (19ii5), for example, was able to distinguish three groups of 

 aquatic flora in Minnesota lakes.' Hardwater flora (in waters with alkalin- 

 ity between 90 and 2^0 parts per million^ sulfate below 50 parts per mil- 

 lion, pH from 8,0 to 8,8) j Soft- water flora (in waters with alkalinity below 

 ho parts per million, sulfate below 5 parts per million, pH below 7 .h) ; and 

 sulfate-water flora (in waters with alkalinity greater than l50 parts per 

 million^ sulfate usually above 125 parts per million, pH from 6.I4 to 9^2) , 

 Knowledge of the minimum threshold r equirements of organisms for various 

 elements is nonexistent j except for indications that they are extremely 

 low. What, then, is known about the individual elements in fresh-water 

 metabolism? 



The apparent success of phosphorus as a fertilizer has made it the 

 center of interest and experiment,, Its main physiological function is to 

 assimilate nitrogen into cellular matter (Hasler and Einsele, I9U8) . 

 Water phosphorus occurs in small quantities (usually less than 1 milli- 

 gram per liter) as organic and phosphate fractions (Welch, 193$) '■> The 

 organic component is further divided into soluble organic and sestonic 

 phosphorus. Many experiments have shown that added phosphate disappears 

 rapidly from the water, usually within a week or two, Zeller's (1953) 

 work indicated a storage of phosphorus in cells during periods of abun- 

 dance with a later growth at the expense of stored material; he also 

 found a constant increase of phosphate in pond bottoms, and attributed 

 this to insolubility and settling of fertilizers. Hasler and Einsele 

 (19ii8) indicated a rapid regeneration of sedimented phosphorus in littoral 



1/ Zeller, H, 1952, Inorganic nutrient levels in fertilized and unfer- 

 tilized farm ponds in central Missouri. Master -s Thesis, Univ, Mo,, 



1U5 pp. 



