264
Use of Radioisotopes to Study Biogeochemical Cycling of Elements
Batches of labeled P04-P should be purchased, containing O.S1 mCi of H 3 33 p04 or H 3 32 p04• For the preparation of the working solution
containing 2-31lCi ml-\ the batch is opened and into it 2 ml of the carrier
solution is added containing 60llg of P04-P (-2 Ilmol ml- 1 ). Then the solution is withdrawn from the container with the aid of a syringe and injected into 100-150ml uf distilled water (for work III freshwaters) or with
3.5% NaCI solution (for work in salt waters). An approximate radioactivity
is controlled in a 0.5-ml portion of its solution dissolved 11100, which is injected into the scintillation vial with the water-miscible cocktail. Then the
solution is filtered through the 0.2-mm pore size membrane filter and distributed into the 1-ml glass ampules, which are sealed and sterilized by
boiling for half an hour, repeated twice with a I-day interval. The radioactivity of the working solution (Rw, cpm ml- I ) can be measured once and
corrected during the time with the use of the corresponding curve of
radioactive disintegration (see Sect. 1.1). The total radioactivity of labeled
phosphate in the experimental samples (R, cpml- 1 ) can be calculated,
knowing the volume of working solution added to a known volume of a
sample. To establish an exact Rw value and to control it with time, O.S ml
of working solution is diluted in SOml of the carrier solution containing
S-lOmgl-1of P04-P The 0.3-0.S-ml aliquots of this dilution are injected
onto the surface of Sartorius membrane filters covered with a thin MgC03
precipitate and placed into the scintillation vials. Then the contents of the
vial is dried, the scintillation cocktail is added into it and it is immediately
radioassayed.
In order to select a proper incubation time for a given water basin,
the curve should be derived as described in the time course of the 33p04_P
uptake. A 1-1 sample of water from the basin under investigation is taken
and charged with an aliquot of working isotope solution. The control 2S0 ml
subsample is also charged being previously fixed with a weak Lugol solution
or with 2 % (end concentration) formalin. The basic sample is placed into the
deck aquarium or in situ incubation. Every 10-20 min, the same two subsamples SO-lOO ml are taken from it and immediately filtered onto the Sartorius cellulose membrane filters 0.2S-0.4S-pore size presoaked in 1 % solution
of N aH2P04• After filtration, the filters are rinsed by subsequent filtration with
S ml of 0.1 % HCl solution, 3 ml of 0.02 % H 3P 04 and 3 ml of filtered natural
water. The solutions of Hel and H 3P 04 are prepared with the same natural
filtered water. The filters are placed into the scintillation vials and radioassayed. The control subsamples are filtered in the same way after the addition
of several drops of thiosulfate solution to kill the iodine. The mean radioactivity of filters corrected for the control one is plotted against the incubation
time to derive the required time curve of 33P04_P uptake by the microplankton. The proper incubation time is selected within its linear part. This incubation time in the eutrophic basins happens to be usually O.S-l h and in the
mesotrophic 1 to 3h. Examples of such time-course curves of P04-P uptake
are given in Fig. S.13.
Use of Radioisotopes to Study Biogeochemical Cycling of Elements
Batches of labeled P04-P should be purchased, containing O.S1 mCi of H 3 33 p04 or H 3 32 p04• For the preparation of the working solution
containing 2-31lCi ml-\ the batch is opened and into it 2 ml of the carrier
solution is added containing 60llg of P04-P (-2 Ilmol ml- 1 ). Then the solution is withdrawn from the container with the aid of a syringe and injected into 100-150ml uf distilled water (for work III freshwaters) or with
3.5% NaCI solution (for work in salt waters). An approximate radioactivity
is controlled in a 0.5-ml portion of its solution dissolved 11100, which is injected into the scintillation vial with the water-miscible cocktail. Then the
solution is filtered through the 0.2-mm pore size membrane filter and distributed into the 1-ml glass ampules, which are sealed and sterilized by
boiling for half an hour, repeated twice with a I-day interval. The radioactivity of the working solution (Rw, cpm ml- I ) can be measured once and
corrected during the time with the use of the corresponding curve of
radioactive disintegration (see Sect. 1.1). The total radioactivity of labeled
phosphate in the experimental samples (R, cpml- 1 ) can be calculated,
knowing the volume of working solution added to a known volume of a
sample. To establish an exact Rw value and to control it with time, O.S ml
of working solution is diluted in SOml of the carrier solution containing
S-lOmgl-1of P04-P The 0.3-0.S-ml aliquots of this dilution are injected
onto the surface of Sartorius membrane filters covered with a thin MgC03
precipitate and placed into the scintillation vials. Then the contents of the
vial is dried, the scintillation cocktail is added into it and it is immediately
radioassayed.
In order to select a proper incubation time for a given water basin,
the curve should be derived as described in the time course of the 33p04_P
uptake. A 1-1 sample of water from the basin under investigation is taken
and charged with an aliquot of working isotope solution. The control 2S0 ml
subsample is also charged being previously fixed with a weak Lugol solution
or with 2 % (end concentration) formalin. The basic sample is placed into the
deck aquarium or in situ incubation. Every 10-20 min, the same two subsamples SO-lOO ml are taken from it and immediately filtered onto the Sartorius cellulose membrane filters 0.2S-0.4S-pore size presoaked in 1 % solution
of N aH2P04• After filtration, the filters are rinsed by subsequent filtration with
S ml of 0.1 % HCl solution, 3 ml of 0.02 % H 3P 04 and 3 ml of filtered natural
water. The solutions of Hel and H 3P 04 are prepared with the same natural
filtered water. The filters are placed into the scintillation vials and radioassayed. The control subsamples are filtered in the same way after the addition
of several drops of thiosulfate solution to kill the iodine. The mean radioactivity of filters corrected for the control one is plotted against the incubation
time to derive the required time curve of 33P04_P uptake by the microplankton. The proper incubation time is selected within its linear part. This incubation time in the eutrophic basins happens to be usually O.S-l h and in the
mesotrophic 1 to 3h. Examples of such time-course curves of P04-P uptake
are given in Fig. S.13.