74
The Radiocarbon Method to Estimate Primary Production
Saruyashi 1956; Datsko 1959; Winberg 1960). This approach was used even as
a kind of reference method to control and even criticize the 14C-bottle method
(Ivanenkov et al. 1972; Gieskes et al. 1979; Tijssen 1979). Indeed, it appeared
to be practical and adequate for estimation of whole community primary production (planktonic and benthic) in shallow high-productive basins such as
coral reefs, coastal marine lagoons, or embayments, shalluw areas of lakes and
rivers (Talling 1957; Winberg 1960; Kinsey and Kinsey 1967; Westlake 1967;
Sorokin 1993); but this approach for evaluation of primary production in open
oceanic waters, especially in oligotrophic ones, does not seem to be feasible.
In the 100-130-m-deep euphotic zone of the ocean, heterotrophic respiration
and exchange with the atmosphere has too high a share in diurnal oxygen
fluctuations in comparison with photosynthesis oxygen production. Therefore
conclusions as to a gross underestimation of primary production as measured
using the 14C-bottle method in tropical (and also in temperate) oceanic waters,
which had been deduced from the measurements of diurnal fluctuations in
oxygen saturation in the mixed layer (Ivanenkov et al. 1972; Gieskes et al.
1979; Tijssen 1979) cannot be accepted as reliable. In this case, minor diurnal
changes recorded in oxygen saturation, like 0.5-1 % calculated per 100-m
water column in the euphotic zone, could result in rather high numbers of
primary production, indicating that the phytoplankton photosynthesis is alone
responsible for these fluctuations; but most probably the main cause of these
fluctuations is the higher respiratory activity of microheterotrophs and migrating zooplankton at night. Concerning the latter, it is obvious, because zooplankton at night migrates from the depth up to the mixed layer. The activity
of microheterotrophs, and especially of planktonic bacteria, as well as the respiration of phytoplankton itself, is inhibited under strong light (Vaccaro and
Ryther 1954; Sorokin 1971; Azam and Holm-Hansen 1973; Harris 1986; Raven
1990). Thus, during the nocturnal period of enhanced respiration, the oxygen
contents in the mixed layer of tropical waters decreases, being then compensated in the daytime by oxygen diffusion from the atmosphere and only in part
by photosynthesis production.
2.5 Use of the Radiocarbon Method to Determine Primary
Production by Benthic Hydrophytes and Their Associations
To estimate primary production by benthic plants, bottom plant associations,
and symbiotic animals, the oxygen bottle method was most often used, which
in principle is equal to that described above (see Sect. 2.4). The objects, stems
of macrophytes, leaves of sea grass, samples of rocks covered with the periphytonic turfs, coral colonies, samples of shallow sediments inhabited by periphytonic micro algae, are incubated in transparent and dark vessels of various
kinds or in plastic film enclosures completely filled with water. Their oxygen
contents is measured by oxygen probes or Winkler titration at the beginning
The Radiocarbon Method to Estimate Primary Production
Saruyashi 1956; Datsko 1959; Winberg 1960). This approach was used even as
a kind of reference method to control and even criticize the 14C-bottle method
(Ivanenkov et al. 1972; Gieskes et al. 1979; Tijssen 1979). Indeed, it appeared
to be practical and adequate for estimation of whole community primary production (planktonic and benthic) in shallow high-productive basins such as
coral reefs, coastal marine lagoons, or embayments, shalluw areas of lakes and
rivers (Talling 1957; Winberg 1960; Kinsey and Kinsey 1967; Westlake 1967;
Sorokin 1993); but this approach for evaluation of primary production in open
oceanic waters, especially in oligotrophic ones, does not seem to be feasible.
In the 100-130-m-deep euphotic zone of the ocean, heterotrophic respiration
and exchange with the atmosphere has too high a share in diurnal oxygen
fluctuations in comparison with photosynthesis oxygen production. Therefore
conclusions as to a gross underestimation of primary production as measured
using the 14C-bottle method in tropical (and also in temperate) oceanic waters,
which had been deduced from the measurements of diurnal fluctuations in
oxygen saturation in the mixed layer (Ivanenkov et al. 1972; Gieskes et al.
1979; Tijssen 1979) cannot be accepted as reliable. In this case, minor diurnal
changes recorded in oxygen saturation, like 0.5-1 % calculated per 100-m
water column in the euphotic zone, could result in rather high numbers of
primary production, indicating that the phytoplankton photosynthesis is alone
responsible for these fluctuations; but most probably the main cause of these
fluctuations is the higher respiratory activity of microheterotrophs and migrating zooplankton at night. Concerning the latter, it is obvious, because zooplankton at night migrates from the depth up to the mixed layer. The activity
of microheterotrophs, and especially of planktonic bacteria, as well as the respiration of phytoplankton itself, is inhibited under strong light (Vaccaro and
Ryther 1954; Sorokin 1971; Azam and Holm-Hansen 1973; Harris 1986; Raven
1990). Thus, during the nocturnal period of enhanced respiration, the oxygen
contents in the mixed layer of tropical waters decreases, being then compensated in the daytime by oxygen diffusion from the atmosphere and only in part
by photosynthesis production.
2.5 Use of the Radiocarbon Method to Determine Primary
Production by Benthic Hydrophytes and Their Associations
To estimate primary production by benthic plants, bottom plant associations,
and symbiotic animals, the oxygen bottle method was most often used, which
in principle is equal to that described above (see Sect. 2.4). The objects, stems
of macrophytes, leaves of sea grass, samples of rocks covered with the periphytonic turfs, coral colonies, samples of shallow sediments inhabited by periphytonic micro algae, are incubated in transparent and dark vessels of various
kinds or in plastic film enclosures completely filled with water. Their oxygen
contents is measured by oxygen probes or Winkler titration at the beginning