Role of Bacteria in Mijieralization of Phosphorus in Lakes 661 



digestion of particulate matter rather than by direct absoi*ption 

 of inorganic or organic sohitions. 



There are now sufficient data, from experiments here de- 

 scribed and the hteraturc, to warrant a prehminary assembly of 

 time relations of the several phosphorus reactions as tliey might 

 occur in a lake or bay. References are given by Hayes and Phillips 

 (5). In Figure 5 the numbers are all days except for one five 

 minute entry. Four kinds of line are used as qualitative indicators 

 of time. It is seen that upon addition of phosphate to water the 

 immediate reaction, within minutes, is a transfer through the 

 bodies of unicellular floating forms of life (heavy lines to right). 

 Next, as shown by the light solid lines to the left, there occurs 

 within a matter of hours, i.e., two orders of magnitude slower 

 than the above, an exchange in which the floating cells and the, 

 higher aquatics compete on approximately equal terms for the 

 PO4. This they make into their own body structures, throwing 

 some of it back to the water as soluble organic phosphorus. We 

 have cancelled out the virtually instantaneous passage through 

 floating cells and set the process down as an equilibrium be- 

 tween inorganic and organic phosphorus in solution, for which 

 the turnover time is 0.3 days. 



At top left is indicated a doubt as to whether higher plants 

 can utilize organic phosphorus, and at top right the feeding of 

 zooplankton is given a turnover time, and their inability to utilize 

 inorganic P is noted. 



The lower part of Figure 5 brings in the sediment surface. 

 At right, bacteria are noted to fall out at a few per cent per day. 

 This is in bottles and not to be read as net fallout in natural 

 waters, which is subject to wide variation. The fallout at right 

 probably describes the same phenomenon as the line leading 

 down at left, i.e., the settling of organic matter to be reduced 

 again by bottom microorganisms for regeneration to the water. 

 The turnover time for leaving the water and for return is here 

 three days, an order of magnitude slower than for exchanges 

 with floating life. 



The inorganic mechanism, which can be observed when 

 bacteria are suppressed, is shown at lower center. The obserxed 

 time relations are not aff^ected by the redox state. In taking out 



