THE PHOSPHORUS FRACTIONS AND THE TURNOVER TIME OF INORGANIC PHOSPHORUS IN DIFFERENT TYPES OF LAKES’

Concentration of three forms of phosphorus was measured in nine lakes throughout one year. The fraction occurring as soluble organic was similar in tight lakes. Results of pre-vious workers wcrc produced by using their methods of separating seston from the water. Use of a filter with 0.1~,u-diameter ports reduced the soluble organic fraction to 18 % of the total. Turnover time of inorganic P was less than 10 min in all lakes during the sum--mer but increased during the winter. Soluble phosphorus in the trophogenic zone of lakes occurs in the inorganic form as orthophosphate and in a form that does not react with acidified molybdatc. In the latter form, it has been called “soluble organic phosphorus ” by Hutchinson ( 1941) and “colloidal phosphorus ” by Einsele ww, although the operational term “soluble reactive ” coined by Strickland and Parsons ( 1960) is probably more dcscrip-tive of our knowledge of this fraction. That inorganic phosphorus is readily used is beyond dispute. In fact, the orthophosphate in the trophogenic zone of lakes is con-tinually taken up and released by plankton, the turnover time of this fraction being as short as 3.6 min (Rigler 1956). However, the availability of naturally occurring solu-ble organic phosphorus has not been adc-quately measured. Watt and Hayes ( 1963) have demonstrated a utilization and pro-duction in seawater fro.m Peggy’s Cove, Nova Scotia, and Overbeck (1962) has demonstrated diurnal fluctuations of solu-ble organic P in a small pond. These and similar observations strongly suggest that ’ soluble organic P in the trophogenic zone of lakes is available and turning over, but they do not tell how much is available or how rapidly it is cycled under natural con-l This work was support&l by grants from th