294
Assay of Some Common Hydrobiological Techniques
absorber is washed down into the flask with the above iodine solution. Final
rinsing of the absorber is carried out with the same iodine solution poured
into it and collected into the same flask. Then the content of the flask is titrated
with 0.1 N thiosulfate solution. The blank flask is titrated after addition of the
same 10-ml portion of Zn-Cd mixture. The content of acid-soluble sulfides (Ks)
.
.
(N -N.)xJ600
IS calculated usmg the formula: Ks =
0
I
mgS- 2 dm- 3 of wet sedV
iment, where No and N; are ml of 0.1 N thiosulfate, used for the blank and
sample titration, and Vs is the volume of sediment thus treated, cm 3 •
If the gravimetric end is preferred, the permanganate solution is washed
down from the absorber into the beaker with 1 ml of 10% BaClz + 1 ml of 112
HCl solution added into it. The contents of the beaker is boiled for 5 min. The
black Mn02 precipitate in it is dissolved with hydrogen peroxide. The precipitate of BaS04 formed is filtered quantitatively at the weighed membrane
filter, which is then dried and weighed again. The weight of BaS04 thus found
is recalculated per weight of sulfur.
The recovery of acid-soluble sulfides by the distillation procedure may be
controlled in the same way as described above for free H 2S measurement; but
in the case, 5-7ml of 5% Na2S9H20 should be used without previous
neutralization.
Besides the calculation of the absolute content of volatile sulfides (AYS)
in the sample (Ks), calculation of the turnover time of their stock (T) is also
of definite interest. The latter may be determined as the ratio T = KslRs days,
where Ks is the stock of acid soluble sulfides in the sediment, mg S dm- 3 , and
Rs the rate of H 2S formation in it due to microbial sulfate reduction (see Sect.
5.6), mgS 2 -dm- 3 day-l.
6.5 Conclusion
This book has presented and discussed the most common ways of applying
radioisotopes for hydro biological research. The use of this technique helps also
to investigate complex problems concerning metabolic pathways in hydrobionts, trophic relationships within the microbial loop, etc., but even what is
here described is quite sufficient to convince those interested in problems of
hydrobiology and aquatic ecology that the radioisotopic technique provides
exclusive advantages in quantification of the basic processes which determine
the productivity and environmental quality of water basins, such as production and decomposition of organic matter and cycling of phosphorus and
sulfur. For this reason alone, it deserves to be actively used in every hydrobiological or environmental laboratory. This is, however, still not the case,
perhaps because people are frightened by the words "radionuclide", "radiation", or by problems caused in some countries by too severe bureaucratic regulations applied to their use in laboratories. However, when refusing to use
Assay of Some Common Hydrobiological Techniques
absorber is washed down into the flask with the above iodine solution. Final
rinsing of the absorber is carried out with the same iodine solution poured
into it and collected into the same flask. Then the content of the flask is titrated
with 0.1 N thiosulfate solution. The blank flask is titrated after addition of the
same 10-ml portion of Zn-Cd mixture. The content of acid-soluble sulfides (Ks)
.
.
(N -N.)xJ600
IS calculated usmg the formula: Ks =
0
I
mgS- 2 dm- 3 of wet sedV
iment, where No and N; are ml of 0.1 N thiosulfate, used for the blank and
sample titration, and Vs is the volume of sediment thus treated, cm 3 •
If the gravimetric end is preferred, the permanganate solution is washed
down from the absorber into the beaker with 1 ml of 10% BaClz + 1 ml of 112
HCl solution added into it. The contents of the beaker is boiled for 5 min. The
black Mn02 precipitate in it is dissolved with hydrogen peroxide. The precipitate of BaS04 formed is filtered quantitatively at the weighed membrane
filter, which is then dried and weighed again. The weight of BaS04 thus found
is recalculated per weight of sulfur.
The recovery of acid-soluble sulfides by the distillation procedure may be
controlled in the same way as described above for free H 2S measurement; but
in the case, 5-7ml of 5% Na2S9H20 should be used without previous
neutralization.
Besides the calculation of the absolute content of volatile sulfides (AYS)
in the sample (Ks), calculation of the turnover time of their stock (T) is also
of definite interest. The latter may be determined as the ratio T = KslRs days,
where Ks is the stock of acid soluble sulfides in the sediment, mg S dm- 3 , and
Rs the rate of H 2S formation in it due to microbial sulfate reduction (see Sect.
5.6), mgS 2 -dm- 3 day-l.
6.5 Conclusion
This book has presented and discussed the most common ways of applying
radioisotopes for hydro biological research. The use of this technique helps also
to investigate complex problems concerning metabolic pathways in hydrobionts, trophic relationships within the microbial loop, etc., but even what is
here described is quite sufficient to convince those interested in problems of
hydrobiology and aquatic ecology that the radioisotopic technique provides
exclusive advantages in quantification of the basic processes which determine
the productivity and environmental quality of water basins, such as production and decomposition of organic matter and cycling of phosphorus and
sulfur. For this reason alone, it deserves to be actively used in every hydrobiological or environmental laboratory. This is, however, still not the case,
perhaps because people are frightened by the words "radionuclide", "radiation", or by problems caused in some countries by too severe bureaucratic regulations applied to their use in laboratories. However, when refusing to use