82
The Radiocarbon Method to Estimate Primary Production
necessary for the approximate coincidence of the intensities of water motion
in the vessel and in situ because the latter can vary greatly in different water
basins and biotopes.
2.5.3 Preparation of Working Solution of 14C-Carbonate
To obtain good counts in plant tissues per counting sample containing 1020mg of dry plant tissue material (some 2-5 x 10 3 cpm), the reverse specific
radioactivity (Cr) of inorganic carbon (see Sects. 2.3.2. and 2.5.1) in the experimental vessels after injection of portions of 14C-carbonate working solution
has to be within the limits of 6 to 10 x 10- 6 mg Ccpm- 1 when working in marine
waters containing -30 mg C 1-1 of T CO2, Correspondingly, in brackish coastal
waters containing -40mg C-T CO2, it must be 8-12 x 10 6 cpm 1-\ and in freshwaters containing 10-15mgCI- 1 of T CO2, 4-6 x 10 6 cpm. The basic working
solution of 14C-carbonate for work with benthic hydrophytes should be prepared within the limits of its radioactivity -15-20 x 10 6 cpm ml- 1 , or 10-15 f.l
Ciml- 1 taking the 70-80% counting efficiency of scintillation spectrometers
into account. Per 11 of water in the experimental vessel, 0.5 ml of this solution
should be injected when working in marine or brackish waters, and half this
amount when working in freshwaters.
The need for purity in the working solution when working with benthic
hydrophytes is much less than with phytoplankton. Therefore ready-for-use
batches of 14C-bicarbonate working solution supplied by specialized agencies
may be used for these experiments without hesitation, if their specific radioactivity is not less than 10 f.lCiml-l. Nevertheless, I recommend using home-made
working solution even in this case, prepared with a simplified procedure. The
advantages will be several times less cost and the possibility of making a solution with optimal specific radioactivity. The concentrated batch of 14C_Na carbonate containing 2-4mCi of nominal dpm radioactivity is simply dissolved
with 100ml alkaline (pH 9.5) carrier solution, containing 20mg Na2C03 in distilled water when working in freshwaters. For use in seawater, 3.5% NaCl is
also added. Its pH should be adjusted with KOH solution if necessary. The
approximate cpm radioactivity of this intermediate radioisotope solution
should then be estimated. For this, 0.1 ml of the solution is diluted in 50ml of
alkaline carrier solution (see above), and 0.5 ml of the latter is radioassayed
in any scintillation cocktail miscible with water. Then the intermediate solution is diluted with the same alkaline carrier solution to the necessary cpm
specific radioactivity (15-20 x 10 6 cpmml- 1 ). This solution is filtered through a
O.2-f.lm pore size membrane filter and distributed into 2-4-ml ampules, which
are then sealed and sterilized by boiling them twice for 20min with a I-day
interval.
The radioactivity of inorganic (T CO2) carbon, R i , for subsequent calculation of Cr should be measured in the working solution once for the whole
The Radiocarbon Method to Estimate Primary Production
necessary for the approximate coincidence of the intensities of water motion
in the vessel and in situ because the latter can vary greatly in different water
basins and biotopes.
2.5.3 Preparation of Working Solution of 14C-Carbonate
To obtain good counts in plant tissues per counting sample containing 1020mg of dry plant tissue material (some 2-5 x 10 3 cpm), the reverse specific
radioactivity (Cr) of inorganic carbon (see Sects. 2.3.2. and 2.5.1) in the experimental vessels after injection of portions of 14C-carbonate working solution
has to be within the limits of 6 to 10 x 10- 6 mg Ccpm- 1 when working in marine
waters containing -30 mg C 1-1 of T CO2, Correspondingly, in brackish coastal
waters containing -40mg C-T CO2, it must be 8-12 x 10 6 cpm 1-\ and in freshwaters containing 10-15mgCI- 1 of T CO2, 4-6 x 10 6 cpm. The basic working
solution of 14C-carbonate for work with benthic hydrophytes should be prepared within the limits of its radioactivity -15-20 x 10 6 cpm ml- 1 , or 10-15 f.l
Ciml- 1 taking the 70-80% counting efficiency of scintillation spectrometers
into account. Per 11 of water in the experimental vessel, 0.5 ml of this solution
should be injected when working in marine or brackish waters, and half this
amount when working in freshwaters.
The need for purity in the working solution when working with benthic
hydrophytes is much less than with phytoplankton. Therefore ready-for-use
batches of 14C-bicarbonate working solution supplied by specialized agencies
may be used for these experiments without hesitation, if their specific radioactivity is not less than 10 f.lCiml-l. Nevertheless, I recommend using home-made
working solution even in this case, prepared with a simplified procedure. The
advantages will be several times less cost and the possibility of making a solution with optimal specific radioactivity. The concentrated batch of 14C_Na carbonate containing 2-4mCi of nominal dpm radioactivity is simply dissolved
with 100ml alkaline (pH 9.5) carrier solution, containing 20mg Na2C03 in distilled water when working in freshwaters. For use in seawater, 3.5% NaCl is
also added. Its pH should be adjusted with KOH solution if necessary. The
approximate cpm radioactivity of this intermediate radioisotope solution
should then be estimated. For this, 0.1 ml of the solution is diluted in 50ml of
alkaline carrier solution (see above), and 0.5 ml of the latter is radioassayed
in any scintillation cocktail miscible with water. Then the intermediate solution is diluted with the same alkaline carrier solution to the necessary cpm
specific radioactivity (15-20 x 10 6 cpmml- 1 ). This solution is filtered through a
O.2-f.lm pore size membrane filter and distributed into 2-4-ml ampules, which
are then sealed and sterilized by boiling them twice for 20min with a I-day
interval.
The radioactivity of inorganic (T CO2) carbon, R i , for subsequent calculation of Cr should be measured in the working solution once for the whole