68
The Radiocarbon Method to Estimate Primary Production
kept at 40°C for 3 h. Then 0.5 ml 10% hyamine solution in methoxyethanol is
added and they are radioassayed, in the same way as the filters with phytoplankton. Experiments with oceanic phytoplankton have proved that the
extradense membrane filters SYNPOR (Czech production) retain over 90%
of the labeled organic matter passed into the filtrate during routine 14C_
primary production filtrations.
6. Grazing impact: fractionation experiments and prescreening of
samples. Sometimes large grazers like planktonic copepods may be present in
the experimental bottles for primary production, and thus graze out a
significant part of the phytoplankton contained in it. For this problem, some
researchers prescreen the subsamples on putting them into the experimental
bottles for primary production experiments with by using plankton nets of
40-100mm mesh. This operation disturbs and mechanically damages the phytoplankton, resulting in a decrease in its photosynthesic activity (Venrick et
al. 1977; Atkinson and Smith 1987), so this procedure should be avoided completely. Samples which have been discovered to contain crustaceans or other
large plankters should be simply ignored. The latter are clearly seen on the
surface of filters after filtration, so the filters must be disposed of. These accidents are not frequent. For basic data, parallel bottles are used. The same must
be said about prescreening water samples for purposes of size fractionation
experiments. This operation causes mechanical damage to the phytoplankton
cells, and thus could result in a distortion of results. The goal of fractionation
experiments is to estimate the shares of various-sized fractions in the whole
primary production. It can be achieved also by postscreening samples after
their incubation in light with 14C-bicarbonate, a much more acceptable way
(Riegman and Colij 1991).
7. Problems in primary production estimation in the water column: photoinhibition and photoadaptation. Both these phenomena are real features in
phytoplankton physiology (Steemann Nielsen and Hansen 1959; Takahashi et
al. 1970; Falkovski 1980; Harris 1980, 1986). In fact, direct sunlight creates in
illumination (PAR) the upper water layer, which exceeds by two to four times
the saturation level for natural phytoplankton. The curve of photosynthesis
rate versus light intensity lies between 1500-3000 ftc, while in full sunlight, its
intensity is 6000 to 9000ftc (50-60 x 10lmmin- 1 see Fig. 2.19). The curves of
phytoplankton photosynthesis rate on vertical profiles (K,) estimated during
in situ 14C-experiments reflect this phenomena of photoinhibition by the
excess of light in upper water layer (Figs 2.10-2.14). In this connection, we
cannot agree with the claim that probably this form of in situ curves, having
maxima at some depth of optimum light, when being measured on a sunny
day could in fact be the same artifact combined with the fixed position of the
experimental bottles in the water column (Harris and Piccinin 1977). In this
case an underestimation of primary production can be expected, especially
when using the calculative method, based on absolute photosynthesis rates
measured only in surface samples (see Sect. 2.3.3.2). However, in my experience, I found K, curves with maxima at same depths also by 2-h exposures of
The Radiocarbon Method to Estimate Primary Production
kept at 40°C for 3 h. Then 0.5 ml 10% hyamine solution in methoxyethanol is
added and they are radioassayed, in the same way as the filters with phytoplankton. Experiments with oceanic phytoplankton have proved that the
extradense membrane filters SYNPOR (Czech production) retain over 90%
of the labeled organic matter passed into the filtrate during routine 14C_
primary production filtrations.
6. Grazing impact: fractionation experiments and prescreening of
samples. Sometimes large grazers like planktonic copepods may be present in
the experimental bottles for primary production, and thus graze out a
significant part of the phytoplankton contained in it. For this problem, some
researchers prescreen the subsamples on putting them into the experimental
bottles for primary production experiments with by using plankton nets of
40-100mm mesh. This operation disturbs and mechanically damages the phytoplankton, resulting in a decrease in its photosynthesic activity (Venrick et
al. 1977; Atkinson and Smith 1987), so this procedure should be avoided completely. Samples which have been discovered to contain crustaceans or other
large plankters should be simply ignored. The latter are clearly seen on the
surface of filters after filtration, so the filters must be disposed of. These accidents are not frequent. For basic data, parallel bottles are used. The same must
be said about prescreening water samples for purposes of size fractionation
experiments. This operation causes mechanical damage to the phytoplankton
cells, and thus could result in a distortion of results. The goal of fractionation
experiments is to estimate the shares of various-sized fractions in the whole
primary production. It can be achieved also by postscreening samples after
their incubation in light with 14C-bicarbonate, a much more acceptable way
(Riegman and Colij 1991).
7. Problems in primary production estimation in the water column: photoinhibition and photoadaptation. Both these phenomena are real features in
phytoplankton physiology (Steemann Nielsen and Hansen 1959; Takahashi et
al. 1970; Falkovski 1980; Harris 1980, 1986). In fact, direct sunlight creates in
illumination (PAR) the upper water layer, which exceeds by two to four times
the saturation level for natural phytoplankton. The curve of photosynthesis
rate versus light intensity lies between 1500-3000 ftc, while in full sunlight, its
intensity is 6000 to 9000ftc (50-60 x 10lmmin- 1 see Fig. 2.19). The curves of
phytoplankton photosynthesis rate on vertical profiles (K,) estimated during
in situ 14C-experiments reflect this phenomena of photoinhibition by the
excess of light in upper water layer (Figs 2.10-2.14). In this connection, we
cannot agree with the claim that probably this form of in situ curves, having
maxima at some depth of optimum light, when being measured on a sunny
day could in fact be the same artifact combined with the fixed position of the
experimental bottles in the water column (Harris and Piccinin 1977). In this
case an underestimation of primary production can be expected, especially
when using the calculative method, based on absolute photosynthesis rates
measured only in surface samples (see Sect. 2.3.3.2). However, in my experience, I found K, curves with maxima at same depths also by 2-h exposures of