Role of Bacteria in Mineralizatioji of Phosphorus in Lakes 655 



cycliiie), plants or zooplaiikton-likc organisms were added as 

 desired. A layer of snperficial lake sediment was eentrihiged to 

 the bottom of the jar to stiuK' exelianges at the mnd-water inter- 

 face. Inorganic P^^O, was added as desired and tlie conrse of its 

 decline in the water followed. 



The water was kept in motion by bubbles of nitrogen or air 

 which had been passed throngh a filter to remove bacteria. 

 Checks were made from time to time on the antibiotics to en- 

 sure that they were botli toxic to bacteria and non-toxic to the ex- 

 perimental plants and invertebrates. For reasons to f(;llow, all 

 samples of P^^-PO. were antoclaved upon delivery and dilution, 

 and kept sterile until use. 



Methods of handling and counting P'", calculations of turn- 

 over times, handling of sediment cores, etc., are given by Coffin 

 etal. (1), Hayes (3), Hayes et al. (4), Harris (2), and Hayes and 

 Phillips (5). 



It is well known that most of the phosphorus in natural 

 waters, say four-fifths to nine-tenths in the summer, is in an or- 

 ganic fomi. There is an inorganic maximum in the winter which 

 quickly declines below the limits of detection when there is 

 enough light to produce a phytoplankton bloom. In an early lab- 

 oratory observation, it was found that three-fifths of the carrier- 

 free phosphate obtained from an atomic pile in normal HCl 

 will, when diluted with distilled water, go over to the organic 

 form within a few days. This is in the absence of any detectable 

 nutrient source. 



The conversion of Pd to organic P was furtlier studied on a 

 jar of lake water which was allowed to settle for twenty-four 

 hours, filtered and kept in the dark. The upper curve of Figure 

 1 shows that after six days, 17 per cent of the P^^ had disappeared 

 from the water, presumably to sessile bacteria growing on the 

 walls. The center curve shows how inorganic phosphorus de- 

 clines, mostly within the first day, to approach an equilibrium 

 in which it is about equal to the organic fraction. The lowest 

 curve is organic P^^ in the water. To find the total organic phos- 

 phorus production, the decline as shown in the top curve should 

 be added to take in the sessile forms. The dotted line gives the 

 revised values. The turnox er time for organic P was calculated at 



