30
The Radiocarbon Method to Estimate Primary Production
The filtered solution is again controlled for pH, which should be about 9. Then
it is distributed into 1-2-ml ampules. The ampules are sealed and pasteurized
twice for 10min in boiling water with a I-day interval. For researchers wanting
to use the above working solution preparation, I recommend first to try it with
a small quantity of 14C-carbonate, ca. 10/-lCi, instead of a real batch, to adapt
the techniques and see the recovery efficiency achieved during this procedure.
For the above amount of 14C-carbonate, it is necessary to mix previously the
unlabeled Na2C03 with 20mg of carrier.
Cleaning of 14C-carbonate preparation can also be done in Conway dishes.
In this case, the sodium hydroxide solution is placed into the central cup. The
batch contents of 14C-carbonate is placed on one side of the internal area of
the dish, the H 2S04 solution on the other. The dish is hermetically closed, and
the batch is mixed with H 2S04.
The radioactivity value of 14C in the working solution (Ri) is needed for
the calculation of photosynthesis rates (see Sect. 2.3.1). It should be estimated
under counting conditions similar to those of the filters with phytoplankton to
determine the radioactivity of 14C assimilated by planktonic algae (R;). In this
case, the problems of counting efficiency, quenching, etc. are avoided (see Sect.
1.2.2.3). The best way for this is to measure Ri in a thin layer of BaC03 sediments of some 3-5mgcm- 2 thick collected at the membrane or the glass fiber
filters. Quenching in such BaC03 sediments is about as low as in 14C-Iabeled
phytoplankton sedimented on filters, e.g., less than 3-5%.
The procedure for Ri estimations in this case is as follows. The exact
amount of working solution (0.5 or l.Oml) is added into the measured 250-ml
flask containing 0.2% alkaline solution of the carrier - nonradioactive sodium
carbonate +20mg/250ml of NaOH. Then the flask is filled up to the mark with
the same alkaline solution, capped, mixed thoroughly, and several parallel subsamples of 0.2-0.5 ml are taken from it with the automatic pipet. The subsamples are inserted into the test tubes into which was previously added 3 ml
distilled water +2ml tap water +lml O.IN KOH (free of carbonates) +0.3ml
0.2% Na2C03. Injection of subsamples into the test tubes is followed by 1 ml
of 10% BaCl2 solution. Then, they are capped, their content is mixed, and they
are incubated at 80°C in a water bath for 20 min. After cooling, the BaC03
sediments formed in them are filtered through O.4-/-lm pore size membrane
filters or glass fiber filters, depending on the kind of filter which is routinely
used for phytoplankton. The filtration should be carried out in a funnel with
the same diameter of working surface as that used for the filtration of phytoplankton (Fig. 2.2). After the end of filtration, the wet filters with BaC03 sediments are placed into the scintillation vials and their radioactivity is counted
with the same kind of scintillation cocktail as used for counting filters with
labeled phytoplankton. The radioactivity of the working solution (Rw) is calculated per 1 ml, accounting for dilution, but without any quenching corrections if the thickness of BaCh sediments does not exceed 5mg BaC03 cm- 2 .
The weight of BaC03 sediments can be regulated by a volume of 0.2 % N a2C03
solution added into the test tubes. The value of Ri for photosynthesis
The Radiocarbon Method to Estimate Primary Production
The filtered solution is again controlled for pH, which should be about 9. Then
it is distributed into 1-2-ml ampules. The ampules are sealed and pasteurized
twice for 10min in boiling water with a I-day interval. For researchers wanting
to use the above working solution preparation, I recommend first to try it with
a small quantity of 14C-carbonate, ca. 10/-lCi, instead of a real batch, to adapt
the techniques and see the recovery efficiency achieved during this procedure.
For the above amount of 14C-carbonate, it is necessary to mix previously the
unlabeled Na2C03 with 20mg of carrier.
Cleaning of 14C-carbonate preparation can also be done in Conway dishes.
In this case, the sodium hydroxide solution is placed into the central cup. The
batch contents of 14C-carbonate is placed on one side of the internal area of
the dish, the H 2S04 solution on the other. The dish is hermetically closed, and
the batch is mixed with H 2S04.
The radioactivity value of 14C in the working solution (Ri) is needed for
the calculation of photosynthesis rates (see Sect. 2.3.1). It should be estimated
under counting conditions similar to those of the filters with phytoplankton to
determine the radioactivity of 14C assimilated by planktonic algae (R;). In this
case, the problems of counting efficiency, quenching, etc. are avoided (see Sect.
1.2.2.3). The best way for this is to measure Ri in a thin layer of BaC03 sediments of some 3-5mgcm- 2 thick collected at the membrane or the glass fiber
filters. Quenching in such BaC03 sediments is about as low as in 14C-Iabeled
phytoplankton sedimented on filters, e.g., less than 3-5%.
The procedure for Ri estimations in this case is as follows. The exact
amount of working solution (0.5 or l.Oml) is added into the measured 250-ml
flask containing 0.2% alkaline solution of the carrier - nonradioactive sodium
carbonate +20mg/250ml of NaOH. Then the flask is filled up to the mark with
the same alkaline solution, capped, mixed thoroughly, and several parallel subsamples of 0.2-0.5 ml are taken from it with the automatic pipet. The subsamples are inserted into the test tubes into which was previously added 3 ml
distilled water +2ml tap water +lml O.IN KOH (free of carbonates) +0.3ml
0.2% Na2C03. Injection of subsamples into the test tubes is followed by 1 ml
of 10% BaCl2 solution. Then, they are capped, their content is mixed, and they
are incubated at 80°C in a water bath for 20 min. After cooling, the BaC03
sediments formed in them are filtered through O.4-/-lm pore size membrane
filters or glass fiber filters, depending on the kind of filter which is routinely
used for phytoplankton. The filtration should be carried out in a funnel with
the same diameter of working surface as that used for the filtration of phytoplankton (Fig. 2.2). After the end of filtration, the wet filters with BaC03 sediments are placed into the scintillation vials and their radioactivity is counted
with the same kind of scintillation cocktail as used for counting filters with
labeled phytoplankton. The radioactivity of the working solution (Rw) is calculated per 1 ml, accounting for dilution, but without any quenching corrections if the thickness of BaCh sediments does not exceed 5mg BaC03 cm- 2 .
The weight of BaC03 sediments can be regulated by a volume of 0.2 % N a2C03
solution added into the test tubes. The value of Ri for photosynthesis