176
Use of Radioisotopic Methodology in Aquatic Microbial Ecology
funnel, the stirrer is started, and the 14C02 thus extracted from the sample is
driven with a stream of air bubbling through it via the funnel into the scintillation vials containing ethanolamine solution in methanol which is attached to
the side arm (Hachett et al. 1977).
2. Decomposition of labeled plant material
Plant material labeled with 14C is obtained during incubation of planktonic
algae, weeds or grasses in water containing 14C-carbonate (see Sect. 3.3). The
plants are chopped up for these experiments; the planktonic algae are concentrated through the OF filters. Then definite amounts of plant material estimated as wet weight or as organic carbon with measured radioactivity in
cpmmg- 1 of biomass are placed into the sample of water or into the thickness
of sediment cores covered with water. Periodically, the 14C02 thus formed and
dissolved in water is extracted and radioassayed as described above. If the
experiment happens to be long-term - weeks or months - the filters with
planktonic algae should be transferred into new portions of water. The water
over the sediment cores should be periodically gently changed. Experiments
of this kind can give valuable information about the duration of the decomposition processes and their efficiency.
3. Evaluation of decomposition rates via estimation of 14C02 dark uptake
Dark 14C uptake in samples of water is estimated mainly as a way to measure
bacterioplankton production (see Sect. 4.4.2). Exactly the same technique
can also be applied to measure the bacterial respiration rate (Mb ), which
can be calculated as follows: Mb = Cd X K mg 0 21- 1 day-I, where Cd is dark
CO2 uptake, mg C 1-1 day-I, and K is the empirical coefficient, corresponding
to the ratio of MblCd (see above, Sect. 4.3.1). This ratio should be estimated
by each researcher personally for a given water body and a given procedure.
For this, the Mb and Cd values are measured in parallel experiments using
the same water, prefiltered gently through a 2.0-2.5-mm pore size Nucleopore
filter with the aid of funnel for inverse filtration (see below, Fig. 6.1). Mb
is measured with the aid of the dark bottle oxygen method (Sorokin and
Kadota 1972; Sepers et al. 1982) at an exposure time of 20-30 h in mesotrophic
waters at 20-25 0c. The technique of Cd estimation is described below as used
for measuring bacterial production (see Sect. 4.4.2), excluding only the
prefiltration at the end of exposure. The ratio of M b , expressed in mg 0 21- 1 day,
to the Cd, expressed as mg of carbon 1-1 day-I, gives the value of needed
coefficient K.
In accordance with a significant finding by Romanenko (1985), a good correlation exists between the overall plankton respiration (e.g., decomposition
rate in water column M t ) and Cd, both estimated in the intact water samples.
The mean for numerous experiments M/Cd ratio was found to be close to 140;
but before deciding to use it, it must be checked by the researcher personally.
Being an empirical value, this ratio depends upon the procedure and upon the
characteristics of the water body under investigation.
Use of Radioisotopic Methodology in Aquatic Microbial Ecology
funnel, the stirrer is started, and the 14C02 thus extracted from the sample is
driven with a stream of air bubbling through it via the funnel into the scintillation vials containing ethanolamine solution in methanol which is attached to
the side arm (Hachett et al. 1977).
2. Decomposition of labeled plant material
Plant material labeled with 14C is obtained during incubation of planktonic
algae, weeds or grasses in water containing 14C-carbonate (see Sect. 3.3). The
plants are chopped up for these experiments; the planktonic algae are concentrated through the OF filters. Then definite amounts of plant material estimated as wet weight or as organic carbon with measured radioactivity in
cpmmg- 1 of biomass are placed into the sample of water or into the thickness
of sediment cores covered with water. Periodically, the 14C02 thus formed and
dissolved in water is extracted and radioassayed as described above. If the
experiment happens to be long-term - weeks or months - the filters with
planktonic algae should be transferred into new portions of water. The water
over the sediment cores should be periodically gently changed. Experiments
of this kind can give valuable information about the duration of the decomposition processes and their efficiency.
3. Evaluation of decomposition rates via estimation of 14C02 dark uptake
Dark 14C uptake in samples of water is estimated mainly as a way to measure
bacterioplankton production (see Sect. 4.4.2). Exactly the same technique
can also be applied to measure the bacterial respiration rate (Mb ), which
can be calculated as follows: Mb = Cd X K mg 0 21- 1 day-I, where Cd is dark
CO2 uptake, mg C 1-1 day-I, and K is the empirical coefficient, corresponding
to the ratio of MblCd (see above, Sect. 4.3.1). This ratio should be estimated
by each researcher personally for a given water body and a given procedure.
For this, the Mb and Cd values are measured in parallel experiments using
the same water, prefiltered gently through a 2.0-2.5-mm pore size Nucleopore
filter with the aid of funnel for inverse filtration (see below, Fig. 6.1). Mb
is measured with the aid of the dark bottle oxygen method (Sorokin and
Kadota 1972; Sepers et al. 1982) at an exposure time of 20-30 h in mesotrophic
waters at 20-25 0c. The technique of Cd estimation is described below as used
for measuring bacterial production (see Sect. 4.4.2), excluding only the
prefiltration at the end of exposure. The ratio of M b , expressed in mg 0 21- 1 day,
to the Cd, expressed as mg of carbon 1-1 day-I, gives the value of needed
coefficient K.
In accordance with a significant finding by Romanenko (1985), a good correlation exists between the overall plankton respiration (e.g., decomposition
rate in water column M t ) and Cd, both estimated in the intact water samples.
The mean for numerous experiments M/Cd ratio was found to be close to 140;
but before deciding to use it, it must be checked by the researcher personally.
Being an empirical value, this ratio depends upon the procedure and upon the
characteristics of the water body under investigation.