Use of the Radiocarbon Method to Determine Primary Production
99
essary to estimate the average wet biomass of the dominating macrophytes (B
kgm-2), the average percentage of dry material in their wet biomass, (D) and
to measure the average Cpm value in them, calculated per units of dry weight
(mgCg- I day-I). Then, Cpt = Cpd D BIlOOgCm- 2 day-I. The calculations of Cpt
will be more simple if the Cpd values have been determined by direct nativein situ measurement of the photosynthesis rate of the macrophyte or sea grass
associations. It is equally simple for microphytobenthos-periphytonic associations, because the Cpd values are also in this case expressed as units of area.
Calculation of photosynthesis rate Cp is carried out with the use of a
formula which accounts for the losses of I4C-assimilates due to experimental
incubations of hydrophytes in the presence of 14C-carbonate (see above).
Therefore the values of photosynthesis thus calculated should be equal to the
gross photosynthesis production. The coincidence of 14C and O 2 estimations of
photosynthesis in macrophytes and microphytobenthos with gross production
had already been stated by Hending and Hargrave (1973), Revsbech and
Jorgensen (1981), Arnold and Littler (1985), and Kemp et al. (1986).
Despite these obstacles, when using the traditional oxygen bottle method,
I strongly recommend making comparative estimations using the oxygen
method to control the data obtained with the aid of 14C-methodology, just to
ensure against some accidental errors in employing the I4C-technique. For such
a comparison I recommend taking as object a fine alga like Cladophora or
Elodea in which gas exchange proceeds faster than in those having massive
thalli. Both parallel incubations (dark - light O 2 and light 14C) should be performed in this case in equal canning jars with exposure for 3-4h during the
first half of the day. To express the oxygen production rates thus measured in
organic carbon units, the photosynthesis quotient P/Q 1.3 may be used.
99
essary to estimate the average wet biomass of the dominating macrophytes (B
kgm-2), the average percentage of dry material in their wet biomass, (D) and
to measure the average Cpm value in them, calculated per units of dry weight
(mgCg- I day-I). Then, Cpt = Cpd D BIlOOgCm- 2 day-I. The calculations of Cpt
will be more simple if the Cpd values have been determined by direct nativein situ measurement of the photosynthesis rate of the macrophyte or sea grass
associations. It is equally simple for microphytobenthos-periphytonic associations, because the Cpd values are also in this case expressed as units of area.
Calculation of photosynthesis rate Cp is carried out with the use of a
formula which accounts for the losses of I4C-assimilates due to experimental
incubations of hydrophytes in the presence of 14C-carbonate (see above).
Therefore the values of photosynthesis thus calculated should be equal to the
gross photosynthesis production. The coincidence of 14C and O 2 estimations of
photosynthesis in macrophytes and microphytobenthos with gross production
had already been stated by Hending and Hargrave (1973), Revsbech and
Jorgensen (1981), Arnold and Littler (1985), and Kemp et al. (1986).
Despite these obstacles, when using the traditional oxygen bottle method,
I strongly recommend making comparative estimations using the oxygen
method to control the data obtained with the aid of 14C-methodology, just to
ensure against some accidental errors in employing the I4C-technique. For such
a comparison I recommend taking as object a fine alga like Cladophora or
Elodea in which gas exchange proceeds faster than in those having massive
thalli. Both parallel incubations (dark - light O 2 and light 14C) should be performed in this case in equal canning jars with exposure for 3-4h during the
first half of the day. To express the oxygen production rates thus measured in
organic carbon units, the photosynthesis quotient P/Q 1.3 may be used.