Environmental Engineering Reference
In-Depth Information
lar environment can be determined from the species
count (
C
) and the mean unit biovolume (
B
′
):
A
A
S
b
=
CB
′
(2.8)
B
Ellipsoid
:
V
=
πAB
2
/6
Scenedesmus bijuga, Euglena
Sphere
:
V
=
πA
3
/6
Sphaerocystis schroeteri
where
S
b
is the total species volume per unit volume
of water (μm
3
ml
−1
),
C
the number of organisms
per unit volume of water (number ml
−1
) and
B
′
the
mean unit biovolume (average volume of an individ-
ual organism, μm
3
).
Some of the limitations involved in the determina-
tion of
B
′
for individual species (variation in size and
shape, approximation to three-dimensional model),
have already been noted and will clearly influence
the accuracy of species population biovolume esti-
mation. The need for accurate species counts (
C
)is
also of paramount importance.
The use of biovolume as an index of species
biomass (dry weight, calculation of particulate
organic carbon) is problematic in algae that have cel-
lular compartments with a high water content. In this
respect, cell volume may be overestimated in larger
cells with large central vacuoles (Smayda, 1978) and
also in mucilaginous algae, which have a high pro-
portion of extracellular watery matrix. In these cases,
alternative biomass estimates can be carried out from
cell dimensions on the basis of cellular surface area
or 'plasma volume'. The latter is the volume of dense
peripheral protoplasm and cell wall material and can
be calculated for algae with prominent vacuoles by
subtraction of the central vacuolar volume from the
total cell volume (Hillebrand
et al
., 1999).
A
A
B
Rod
:
V
=
πAB
2
/4
Melosira granulata, Cyclotella
B
Two cones
:
V
=
πAB
2
/12
Ankistrodesmus falcatus
A
A
B
B
Single cone
:
V
=
πAB
2
/12
Horn of
Ceratium hirundinella
Ellipsoid/cone
:
V
= [
πB
2
(
A
+
B
/2)]/12
Rhodomonas minuta, Synura
A
A
B
C
Irregular
:
V
=
BC
(
A
−
B
+
π
/4.
B
)
Achnanthes B
/
C
− face/side view
B
Irregular
:
V
=
πAB
2
/9
Peridinium
Figure 2.17
Standard shapes for calculating algal bio-
volumes: some common examples.
In calculating species mean unit biovolume, linear
measurements should be made from a range of cells
within the species population, and images should be
obtained of cells with different orientations to decide
the best combination of geometric shapes or mea-
surements that fit the cells in that population. In cases
where cell shape cannot be easily represented by
means of a geometric formula, for example
Cymbella
and
Amphora
, best estimates have to be made. It may
also be useful to make plastic models to determine
unit volume (Bellinger, 1974).
Totalphytoplankton biovolume
For a partic-
ular mixed phytoplankton sample, the total phyto-
plankton biovolume (
P
b
) can simply be derived as
the sum of all the species biovolumes (
S
b
,
S
b
, etc.):
P
b
=
∑
S
b
,
S
b
,
S
b
⋯
S
b
(2.9)
Biovolumes (
P
b
- expressed as μm
3
ml
−1
) can be
converted to fresh weight or dry weight (μg
3
ml
−1
)
using appropriate conversion factors if required.
Calculation of total phytoplankton biovolume (
P
b
)
provides an indirect assessment of phytoplankton
biomass since it is based on separate determinations
Species population biovolume
Calculation of
total species population biovolume (
S
b
) in a particu-
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