50 ml
Technique of Measuring Phytoplankton Primary Production
31
to vacuum
Fig. 2.2. Plexiglas funnel for filtration of BaC03
precipitates
calculation is equal to R; = Rw V cpm, if V is the volume of a portion of working
solution added into the sample in ml.
In practice with the 14C-method, many researchers have estimated the Rw
values by direct injection of portions of diluted working solution into the scintillation cocktail, instantly measuring then the radioactivity in the counting
sample. In this case, an overestimation of Rw (and, correspondingly, an underestimation of the photosynthesis rate in phytoplankton) should be expected
at a level of 20-30% because of the difference in the geometry of counting,
and of a higher counting efficiency of homogenous counting samples in comparison with the two-phase ones.
2.3.2.2 Estimation of Total Hydrocarbonate Carbon Contents in Water (C;)
The value of C; is needed to calculate the specific radioactivity of inorganic
carbon in the pool of hydrocarbonates (see Sect. 2.3.1). It is measured as the
sum of dissolved CO2 + HCO} + cOj-. In oceanic waters, the value of R; can
be calculated from data on pH, alkalinity, and salinity by oceanographic tables
or nomograms. For waters of the open ocean with salinity between 33 and
35%, C; is close to 28mgCl- 1 with small deviations which can be ignored. This
value may be used as a standard for calculating primary production in oceanic
waters. In internal seas, and especially in coastal and brackish estuarine waters
with variable salinity and ionic water composition, there is every reason to
determine the C; in water with the aid of some analytical procedure, like titration, or infrared or coulometric analyses.
The titration of total CO2 can be accomplished as follows (Sorokin 1955a).
To 100mi of subs ample the phenolphthalein indicator is first added (several
Technique of Measuring Phytoplankton Primary Production
31
to vacuum
Fig. 2.2. Plexiglas funnel for filtration of BaC03
precipitates
calculation is equal to R; = Rw V cpm, if V is the volume of a portion of working
solution added into the sample in ml.
In practice with the 14C-method, many researchers have estimated the Rw
values by direct injection of portions of diluted working solution into the scintillation cocktail, instantly measuring then the radioactivity in the counting
sample. In this case, an overestimation of Rw (and, correspondingly, an underestimation of the photosynthesis rate in phytoplankton) should be expected
at a level of 20-30% because of the difference in the geometry of counting,
and of a higher counting efficiency of homogenous counting samples in comparison with the two-phase ones.
2.3.2.2 Estimation of Total Hydrocarbonate Carbon Contents in Water (C;)
The value of C; is needed to calculate the specific radioactivity of inorganic
carbon in the pool of hydrocarbonates (see Sect. 2.3.1). It is measured as the
sum of dissolved CO2 + HCO} + cOj-. In oceanic waters, the value of R; can
be calculated from data on pH, alkalinity, and salinity by oceanographic tables
or nomograms. For waters of the open ocean with salinity between 33 and
35%, C; is close to 28mgCl- 1 with small deviations which can be ignored. This
value may be used as a standard for calculating primary production in oceanic
waters. In internal seas, and especially in coastal and brackish estuarine waters
with variable salinity and ionic water composition, there is every reason to
determine the C; in water with the aid of some analytical procedure, like titration, or infrared or coulometric analyses.
The titration of total CO2 can be accomplished as follows (Sorokin 1955a).
To 100mi of subs ample the phenolphthalein indicator is first added (several