290
Assay of Some Common Hydrobiological Techniques
matter in the water accessible to immediate microbial metabolic transformation and decomposition (LOM) can be ascertained. If we refer to the typical
BOD time course curve we will see that within the first 2-3 days at 18-20°C,
it makes a straight line, which then bends (Fig. 6.9). So, when measuring BOD
at in situ temperature within an incubation time of about 1 day, we are able
to measure the absolute rate of decomposition of organic matter, ur the rate
of TPM, because just this process is responsible for the above decomposition.
The TPM can be expressed as mg 0 2 1- 1 day-lor as mg C 1-1 day-I, assuming
the proper RQ quotient. Being measured on the vertical profile, it may be
expressed in the same units as primary production (Pt ), e.g., in gCm- 2 day-l.
In this case, the ratio TPMIPt is evidence for the relative role of the moment
autochthonous production as energy source in a given ecosystem. This index
may be more exact, being corrected also for bottom respiration (TBM): TBM
+ TPMIPt•
Returnign to the BOD time-course curve (Fig. 6.9) it levels and after 20-30
days of incubation at to 18-20 0c. This means that all accessible for rapid microbial action stock of labile organic matter has been exhausted during this time.
Thus, the BOD measured after 30 days of incubation at the above-mentioned
temperature corresponds to an initial stock of labile organic matter (LOM) in
the water sample. So in this case measuring BOD for 30 days gives values close
to the size of the stock of LOM in a water sample, unlike BOD-5, which
corresponds neither to the decomposition rate (the curve also bends), nor to
the stock of LOM (which still does not level out). To translate the values of
BOD-30 to the values of LOM stock expressed in carbon units, it is necessary
to account also for the expenditure of a part of LOM stock assimilated by
bacteria for their cell synthesis due to the bottle experiments.
BOD
1,6
1,2
0,8
0,4
t
12
18
24
30
Fig. 6.9. Typical time course of BOD (mg021-1), as measured in a coastal area of the
Black Sea. t Incubation time, days
Assay of Some Common Hydrobiological Techniques
matter in the water accessible to immediate microbial metabolic transformation and decomposition (LOM) can be ascertained. If we refer to the typical
BOD time course curve we will see that within the first 2-3 days at 18-20°C,
it makes a straight line, which then bends (Fig. 6.9). So, when measuring BOD
at in situ temperature within an incubation time of about 1 day, we are able
to measure the absolute rate of decomposition of organic matter, ur the rate
of TPM, because just this process is responsible for the above decomposition.
The TPM can be expressed as mg 0 2 1- 1 day-lor as mg C 1-1 day-I, assuming
the proper RQ quotient. Being measured on the vertical profile, it may be
expressed in the same units as primary production (Pt ), e.g., in gCm- 2 day-l.
In this case, the ratio TPMIPt is evidence for the relative role of the moment
autochthonous production as energy source in a given ecosystem. This index
may be more exact, being corrected also for bottom respiration (TBM): TBM
+ TPMIPt•
Returnign to the BOD time-course curve (Fig. 6.9) it levels and after 20-30
days of incubation at to 18-20 0c. This means that all accessible for rapid microbial action stock of labile organic matter has been exhausted during this time.
Thus, the BOD measured after 30 days of incubation at the above-mentioned
temperature corresponds to an initial stock of labile organic matter (LOM) in
the water sample. So in this case measuring BOD for 30 days gives values close
to the size of the stock of LOM in a water sample, unlike BOD-5, which
corresponds neither to the decomposition rate (the curve also bends), nor to
the stock of LOM (which still does not level out). To translate the values of
BOD-30 to the values of LOM stock expressed in carbon units, it is necessary
to account also for the expenditure of a part of LOM stock assimilated by
bacteria for their cell synthesis due to the bottle experiments.
BOD
1,6
1,2
0,8
0,4
t
12
18
24
30
Fig. 6.9. Typical time course of BOD (mg021-1), as measured in a coastal area of the
Black Sea. t Incubation time, days