and solid (including living matter) fractions. In their experiments, the 

 turnover time for soluble P32 was ^.U days, and 39 days for the p32 in 

 solids. Less than one-sixth of the added phosphorus was in solution at 

 any one time. Considering the results of other experiments, these workers 

 calculated turnover times for phosphorus in solids up to 176 days, and 

 for dissolved phosphorus to 30 days. From Uo7 to 8o7 times as much phos- 

 phorus was turning over as was in solution. McCarter et al, (1952) 

 analyzed the hypolimnetic muds and concluded that the P-^'^ had not pene- 

 trated much beyond 1 millimeter. 



The phosphorus picture can be reduced to greater simplicity; 



1, The case history of fertilization supports phosphorus as the most 

 essential common fertilizing element, 



2, Small quantities exist in natural waters, mainly in two forms, organic 

 phosphorus and phosphate. The former is more abundant, but the latter 

 is more active and often minimal or limiting to productive capacity. 

 Phosphate may become bound in insoluble compounds, and this loss may 

 be related to the alkalinity of the water and to the marl organic 

 matter ratio; of the substrate. 



3, Apparently, most phosphate is absorbed directly by lower organisms 

 and indirectly by fish which feed upon them. The direct absorption 

 occurs in minutes or hours. Fauna can concentrate phosphorus in far 

 greater amounts than can flora, 



U, The dynamic state of phosphorus has been describerl. The environment 



has a great affinity for phosphorus, most of it rapidly entering solids. 

 A continuous phosphorus exchange occurs between water and solids. Since 

 the amount of phosphorus in solution is small, the turnover rate for 

 dissolved phosphorus is more rapid than that for phosphorus in solids. 



Nitrogen, as a basic constituent of protein, is necessary for the 

 formation of living matter (Meehean, 1935) • It occurs as a free element 

 (N) , or as amraonia (NH3) , nitrate (NO^) , nitrite (NO2) ; and organic ni- 

 trogen. These form a well-known cycle related to bacterial activity. 

 Nitrification proceeds in the order named, by the action of nitrogen- 

 fixing and nitrifying bacteria. Welch (1935) listed molds and possible 

 algae as nitrogen fixers. Nitrate and nitrite nitrogen (especially the 

 former) are generally accepted as the available forins of nitrogen for 

 anabolic activity of higher organisms, Pennington (19li2) found that 

 cultures of algae and bacteria utilized amraonia nitrogen more rapidly 

 than nitrate nitrogen. Denitrification acts in the reverse order with 

 denitrifying bacteria changing organic nitrogen into ammonia. According 

 to Welch (1935), free nitrogen is barely soluble and enters the water 

 from the atmosphere, Aninonia, he stated, is highly soluble and toxic to 

 fish in relatively small amounts (8 p.p,m.). The nitrate nitrogen con- 

 tent of water is low and usually variable. 



