MAP Technical Reports Series No. 106 UNEP

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Appendix I
MEASUREMENTS OF BIOMASS
It is not the place here to enter into methodological questions of how to measure
biomass in the aquatic environment. The reader can find pertinent information in several
Handbooks. Nevertheless, it seems advisable to give at least some hints to current
measurement concepts, as an comprehension of this matter is crucial from both, theoretical and
practical considerations.
Among the respective problems to mention are those regarding, e.g., consistency,
comparability and interpretability of data gathered. This entails several elements: a) statistical
significance of the one sample; b) variability of replicates; c) variability of the surroundings; d)
data cohesiveness over a larger spatial segments (which are either homogenous,
inhomogeneous, or characterized by gradients); e) variability in time over the same spatial unity.
These points are pertinent all measurements, regardless of whether the biological
entities in question are phytoplankton, macrophytes, zooplankton, bottom fauna, fish, bacteria,
or else.
Further it is to be noted that non of the various measurements listed below is a perfect
expression of biomass. Indeed, biomass per se is not measurable. Biomass can only by
interpreted from substitute measurements of miscellaneous quality and comparability. Because
of limited analytical capability (either in terms of instrumentation, manpower and logistic
resources), actual measurements are often restricted to some components; others are
estimated indirectly using conversion factors. This may, or may not be justifiable in the light of
present knowledge. To note: simple conversion from one dimension to another does not add
new information. Therefore uncritical use of converted data can be misleading.
The following are a view remarks to the most common measurement types and
respective notions.
(a) Gross measurements
(i) Counts and biomass volume
(ii) Wet and dry weight
(b) Substitute measures
(iii) Pigments
(iv) Elemental composition (POC, PON, POP)
(v) ATP
(vi) Biochemical components
The classical methods to quantify biomass is counting of numbers of specimens per
species found per unit of volume or surface. This presupposes, of course, identification of
species. This latter is primarily a taxonomic problem that requires experience. Taxonomic
expertise is diminishing among aquatic biologist; still, specialists in various fields of taxonomy
exist around the world, which in case of uncertainty have to be contacted.