88
The Radiocarbon Method to Estimate Primary Production
ton, and in open cores of bottom sediments with microphytobenthos; however,
from my personal experience, more convenient and efficient are incubations
in larger open aquaria, which can even have sand on the bottom if Ci values
in them are controlled at the beginning and end of incubation. Incubation conditions in the aquaria are closer to those in situ. The possibility of using open
aquaria for 14C-uptake experiments with hydrophytes has been discussed
above (see Sect. 2.5.2). When having only one large open aquarium, it is possible to measure in one set the photosynthesis rate either in many equal specimens of the same species (parallel estimations), or in many specimens of
various species and also in other, different objects like periphyton or microphytobenthos simply by placing their samples into the same aquarium of ca.
15-20·1 capacity. Such an aquarium for common incubations, when installed
on a separate stand (Fig. 2.21), has accessories for stirring, pumping water (for
calculation), and bubbling air. The aquarium is filled with prefiltered ambiental water, as described above, 2-3 cm over the sea level. Then the experimental specimens are randomly placed on its bottom. The appropriate amount of
diluted working radioisotope solution is added first to 1-2·1 of the same water
contained in a separate jar. After mixing, the contents of the jar are poured
into the stirring water column in the aquarium, the water column is thoroughly
mixed, and the experiment starts.
Sediment cores with microphytobenthos can be collected with the help of
two kinds of plastic tubes: whole ones and those separable into two parts. The
cores are taken as described above (Fig. 2.24), their lower end being closed
with rubber stoppers. The cores are treated variously, depending on the kind
of sediment sampled. In muddy sediments, microphytobenthos associations
develop only within the upper millimeter, forming fine films or turfs on the
surface (Van Raalte et a1. 1974; Plante-Cuny 1984). Light does not penetrate
more deeply into them and photosynthesis proceeds only in this upper film.
In this case, the Cr of 14C-carbonates thus consumed by the algae of microphytobenthos will be about the same as in the water column. The incubation
experiment with cores taken with whole tubes is started as follows. First with
the aid of a syphon with a hook at its lower end, the water over the sediment
is carefully discharged, not disturbing its surface. Then with the aid of another
tube, with a special small platform on its lower end to brake the jet current
going from it, the core tube is filled with new prefiltered water, to which the
necessary amount of 14C working solution has previously been added. The first
portion of this water should be let into the tube extremely slowly so as not to
disturb the film of microalgae over the sediment. The tube, filled to 2-4 cm
below the rim, is covered with a plastic cup or with polyethylene film fixed
with a rubber band, then placed for incubation on the stand, and fixed with
special holders.
If a muddy sediment sample is taken with a separable corer tube, the procedure is simpler. The upper part of the tube is screwed out and separated. In
its lower, shorter part, the core of sediment remains with some 2-3 cm of water
layer above. This core is placed directly into the aquarium or a vessel with
The Radiocarbon Method to Estimate Primary Production
ton, and in open cores of bottom sediments with microphytobenthos; however,
from my personal experience, more convenient and efficient are incubations
in larger open aquaria, which can even have sand on the bottom if Ci values
in them are controlled at the beginning and end of incubation. Incubation conditions in the aquaria are closer to those in situ. The possibility of using open
aquaria for 14C-uptake experiments with hydrophytes has been discussed
above (see Sect. 2.5.2). When having only one large open aquarium, it is possible to measure in one set the photosynthesis rate either in many equal specimens of the same species (parallel estimations), or in many specimens of
various species and also in other, different objects like periphyton or microphytobenthos simply by placing their samples into the same aquarium of ca.
15-20·1 capacity. Such an aquarium for common incubations, when installed
on a separate stand (Fig. 2.21), has accessories for stirring, pumping water (for
calculation), and bubbling air. The aquarium is filled with prefiltered ambiental water, as described above, 2-3 cm over the sea level. Then the experimental specimens are randomly placed on its bottom. The appropriate amount of
diluted working radioisotope solution is added first to 1-2·1 of the same water
contained in a separate jar. After mixing, the contents of the jar are poured
into the stirring water column in the aquarium, the water column is thoroughly
mixed, and the experiment starts.
Sediment cores with microphytobenthos can be collected with the help of
two kinds of plastic tubes: whole ones and those separable into two parts. The
cores are taken as described above (Fig. 2.24), their lower end being closed
with rubber stoppers. The cores are treated variously, depending on the kind
of sediment sampled. In muddy sediments, microphytobenthos associations
develop only within the upper millimeter, forming fine films or turfs on the
surface (Van Raalte et a1. 1974; Plante-Cuny 1984). Light does not penetrate
more deeply into them and photosynthesis proceeds only in this upper film.
In this case, the Cr of 14C-carbonates thus consumed by the algae of microphytobenthos will be about the same as in the water column. The incubation
experiment with cores taken with whole tubes is started as follows. First with
the aid of a syphon with a hook at its lower end, the water over the sediment
is carefully discharged, not disturbing its surface. Then with the aid of another
tube, with a special small platform on its lower end to brake the jet current
going from it, the core tube is filled with new prefiltered water, to which the
necessary amount of 14C working solution has previously been added. The first
portion of this water should be let into the tube extremely slowly so as not to
disturb the film of microalgae over the sediment. The tube, filled to 2-4 cm
below the rim, is covered with a plastic cup or with polyethylene film fixed
with a rubber band, then placed for incubation on the stand, and fixed with
special holders.
If a muddy sediment sample is taken with a separable corer tube, the procedure is simpler. The upper part of the tube is screwed out and separated. In
its lower, shorter part, the core of sediment remains with some 2-3 cm of water
layer above. This core is placed directly into the aquarium or a vessel with