26
The Radiocarbon Method to Estimate Primary Production
thus covering practically all possible deficiencies. The problems of the adequacy of 14C and oxygen bottle methods are discussed in more detail below
(see Sect. 2.4).
The main goal of primary production measurement is to estimate its integrated rate in the whole water column (Cpt) in g C m- 2 day-I, because just this
value is equal to the primary autochthonous energy mput mto the ecosystem.
This value can be achieved directly via the measurement of photosynthesis
rates at depth intervals within the euphotic zone by in situ exposures of experimental bottles on vertical profiles. It might also be calculated from the
absolute rate of photosynthesis, measured only in surface samples (Cpsmg
Cm- 3 day-I), and the relative photosynthesis rates on vertical profiles (Ks). The
radiocarbon method appeared to be very efficient for this kind of estimation
because of its high sensitivity and minimal time costs. During the following
description of 14C-methodology for primary production measurements, we differentiate between two kinds of estimations: of absolute rates in the samples
of water (Cps) and of relative rates on vertical profiles (Ks).
2.3 Technique of Measuring Phytoplankton Primary
Production
2.3.1 General Principles
Estimation of the rate of phytoplankton photosynthesis in samples of water
with the aid of 14C is based on labeling inorganic carbon with this isotope in
the pool of hydrocarbonates. This pool exists in natural waters in three forms:
free dissolved CO2, bicarbonate (HCOn, and carbonate (C03 2 +). After the
injection of a portion of working solution of labeled 14C-carbonate into the
water sample, within several seconds, all the above three forms of CO2 within
it become equally labeled via the exchange relations, thus being equilibrated
in respect of their inverse specific radioactivity (C). The latter is equal to the
ratio: Cr = C;lR;mgCcpm-l, if: C; is total content of hydrocarbonate inorganic
carbon (T CO2) in the sample of water, mg CI- 1 , and R; the radioactivity of 14C
added to it as 14C032-, cpml- l . Thus, to each cpm of 14C radioactivity in this
sample a definite amount of inorganic carbon corresponds. If this labeled
inorganic carbon is transformed into the organic form by phytoplankton cells
present in it, its absolute amount (Cp ) can be easily calculated if the radioactivity (Rp) of this newly formed organic matter is measured: Cp = Rp Crmg C.
During the process of autotrophic biosynthesis of organic matter, 14C02 is
acquired by algal cells from the labeled hydrocarbonate pool of the sample
with some change in its specific radioactivity. The 14C atoms of labeled 14C02
are a little heavier than those of the normal 12C-C02• Therefore, the bioassimilation of labeled 14CO-molecules during photosynthesis proceeds some
The Radiocarbon Method to Estimate Primary Production
thus covering practically all possible deficiencies. The problems of the adequacy of 14C and oxygen bottle methods are discussed in more detail below
(see Sect. 2.4).
The main goal of primary production measurement is to estimate its integrated rate in the whole water column (Cpt) in g C m- 2 day-I, because just this
value is equal to the primary autochthonous energy mput mto the ecosystem.
This value can be achieved directly via the measurement of photosynthesis
rates at depth intervals within the euphotic zone by in situ exposures of experimental bottles on vertical profiles. It might also be calculated from the
absolute rate of photosynthesis, measured only in surface samples (Cpsmg
Cm- 3 day-I), and the relative photosynthesis rates on vertical profiles (Ks). The
radiocarbon method appeared to be very efficient for this kind of estimation
because of its high sensitivity and minimal time costs. During the following
description of 14C-methodology for primary production measurements, we differentiate between two kinds of estimations: of absolute rates in the samples
of water (Cps) and of relative rates on vertical profiles (Ks).
2.3 Technique of Measuring Phytoplankton Primary
Production
2.3.1 General Principles
Estimation of the rate of phytoplankton photosynthesis in samples of water
with the aid of 14C is based on labeling inorganic carbon with this isotope in
the pool of hydrocarbonates. This pool exists in natural waters in three forms:
free dissolved CO2, bicarbonate (HCOn, and carbonate (C03 2 +). After the
injection of a portion of working solution of labeled 14C-carbonate into the
water sample, within several seconds, all the above three forms of CO2 within
it become equally labeled via the exchange relations, thus being equilibrated
in respect of their inverse specific radioactivity (C). The latter is equal to the
ratio: Cr = C;lR;mgCcpm-l, if: C; is total content of hydrocarbonate inorganic
carbon (T CO2) in the sample of water, mg CI- 1 , and R; the radioactivity of 14C
added to it as 14C032-, cpml- l . Thus, to each cpm of 14C radioactivity in this
sample a definite amount of inorganic carbon corresponds. If this labeled
inorganic carbon is transformed into the organic form by phytoplankton cells
present in it, its absolute amount (Cp ) can be easily calculated if the radioactivity (Rp) of this newly formed organic matter is measured: Cp = Rp Crmg C.
During the process of autotrophic biosynthesis of organic matter, 14C02 is
acquired by algal cells from the labeled hydrocarbonate pool of the sample
with some change in its specific radioactivity. The 14C atoms of labeled 14C02
are a little heavier than those of the normal 12C-C02• Therefore, the bioassimilation of labeled 14CO-molecules during photosynthesis proceeds some