78
The Radiocarbon Method to Estimate Primary Production
situ or sampled carefully without serious disturbances, and incubated in
aquaria or other vessels outside the native basin under conditions simulating
those in situ. The latter approach is very convenient for estimating primary
production in associations of microphytobenthos or periphyton. First, the incubation of a given undisturbed plant association in water containing 14C_
carbonate with an estimated specific radioactivity Cr is carried out. When the
incubation is finished, the plants are extracted, sorted by species or kinds
(grasses, macrophytes, periphytonic turfs, coralline algae microphytobenthos,
etc.), and frozen. Then their radioactivity (Rc) may be measured and their photosynthesis rates Cp may be calculated separately for each individual species
or group composing this plant association.
2.5.2 Experimental Vessels and Enclosures
To carry out the necessary estimations with the aid of the radiocarbon method,
suitable experimental vessels should first be selected. To measure photosynthesis rates in individual plants, in samples of periphytonic overgrowths on
hard substrates or of microphytobenthos, glass preservting jars of 2-5-1 capacity can be used. The jars should be supplied with Plexiglas lids with silicon
rubber rings at the rim contacting with the jar and supplied with clasps on both
sides to be locked on to the jar (Fig. 2.20). The jars can be replaced by various
sized cylinders, square vessels, or chambers made of the Plexiglas, which may
be more handy for use in the field, being less fragile in comparison with
the glass ones. The main problem in the use of Plexiglas containers is their
potential toxicity when new. Therefore new Plexiglas vessels for primary production incubations must be kept immersed in water for at least 2 weeks
before use. To check new Plexiglas containers for toxicity, a parallel estimation of 14C-uptake rates by two equal shoots of some macrophyte can be made,
incubating one in a glass jar, and the other in a plastic container of the same
capacity.
Plexiglas vessels to be used as in situ enclosures to isolate one area of the
basin floor together with the plants inhabiting it can be constructed with or
without upper lids. The upper lid is necessary if the vessel is to be incubated
deeper under the water surface, but in shallows, tube vessels of cylinder or
square form can be used, with a cross-section of 300 to 500cm 2 • At depths of
20-40cm their upper edge should be 5-lOcm over the water surface. Such tube
vessels may be used in experiments with an open upper surface without lids,
which is very convenient for experimental work in situ. This is possible because
of the above mentioned stability of reverse specific radioactivity (Cr) in natural
waters in contact with the atmosphere. The lower end of the tube-like vessels,
as in vessels with an upper lid, should be worked into the bottom sediments
for at least 8-10 cm to prevent exchange between the contained volume of
water and the surrounding one. In this case passing waves create a difference
The Radiocarbon Method to Estimate Primary Production
situ or sampled carefully without serious disturbances, and incubated in
aquaria or other vessels outside the native basin under conditions simulating
those in situ. The latter approach is very convenient for estimating primary
production in associations of microphytobenthos or periphyton. First, the incubation of a given undisturbed plant association in water containing 14C_
carbonate with an estimated specific radioactivity Cr is carried out. When the
incubation is finished, the plants are extracted, sorted by species or kinds
(grasses, macrophytes, periphytonic turfs, coralline algae microphytobenthos,
etc.), and frozen. Then their radioactivity (Rc) may be measured and their photosynthesis rates Cp may be calculated separately for each individual species
or group composing this plant association.
2.5.2 Experimental Vessels and Enclosures
To carry out the necessary estimations with the aid of the radiocarbon method,
suitable experimental vessels should first be selected. To measure photosynthesis rates in individual plants, in samples of periphytonic overgrowths on
hard substrates or of microphytobenthos, glass preservting jars of 2-5-1 capacity can be used. The jars should be supplied with Plexiglas lids with silicon
rubber rings at the rim contacting with the jar and supplied with clasps on both
sides to be locked on to the jar (Fig. 2.20). The jars can be replaced by various
sized cylinders, square vessels, or chambers made of the Plexiglas, which may
be more handy for use in the field, being less fragile in comparison with
the glass ones. The main problem in the use of Plexiglas containers is their
potential toxicity when new. Therefore new Plexiglas vessels for primary production incubations must be kept immersed in water for at least 2 weeks
before use. To check new Plexiglas containers for toxicity, a parallel estimation of 14C-uptake rates by two equal shoots of some macrophyte can be made,
incubating one in a glass jar, and the other in a plastic container of the same
capacity.
Plexiglas vessels to be used as in situ enclosures to isolate one area of the
basin floor together with the plants inhabiting it can be constructed with or
without upper lids. The upper lid is necessary if the vessel is to be incubated
deeper under the water surface, but in shallows, tube vessels of cylinder or
square form can be used, with a cross-section of 300 to 500cm 2 • At depths of
20-40cm their upper edge should be 5-lOcm over the water surface. Such tube
vessels may be used in experiments with an open upper surface without lids,
which is very convenient for experimental work in situ. This is possible because
of the above mentioned stability of reverse specific radioactivity (Cr) in natural
waters in contact with the atmosphere. The lower end of the tube-like vessels,
as in vessels with an upper lid, should be worked into the bottom sediments
for at least 8-10 cm to prevent exchange between the contained volume of
water and the surrounding one. In this case passing waves create a difference