Biological field and laboratory methods for measuring the quality of ...

pipet with distilled water into a culture dish to
remove any adherent organisms. Enumerate
(about 200 zooplankters) and identify under a
dissecting microscope.
To calculate the number of plankton with an
unmetered collecting device:
DV
Total no. = SV X TN
To calculate the number of plankton with a
metered collecting device:
Noo per m3 of water =
TN XDV
SV
Q
where:
DV = total diluted volume, ml
SV = total subsample volume, ml
TN = total no. zooplankters in sample
Q =quantity of water strained, m 3
Counting Chamber
Bring the entire concentrate (or an appropriate
aliquot) to a volume of 8 ml, mix well,
and transfer to a counting chamber 80 X 50 X 2
mm (8-ml capacity). To fill, use the technique
previously described for the Sedgwick-Rafter
cell. The proper degree of sample concentration
can be determined only by experience.
Using a compound microscope equipped with
an ocular Whipple grid, enumerate and identify
the rotifers (to species if possible) in IO strips
scanned at a magnification of 100X (one-fifth of
the chamber volume). Enumerate the nauplii
also during the rotifer count. Count the adult
microscrustacea under a binocular dissecting
microscope at a magnification of 20 to 40X by
scanning the entire chamber. Species identification
of rotifers and microcrustacea often
require dissection and examination under a
compound microscope (see Pennak, 1953).
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PLANKTON BIOMASS
When calculating the number of plankton,
determine the volume of the counting chamber
from its inside dimensions. Convert the tallies to
organisms per liter with the use of the following
relationships:
TXC
Rif ot ers per Iiter
=--
pxv
o
M
1° T
Icrocrustacea per Iter
xc
= S X V
where:
T:: total tally
C:: total volume of sample concentrate, ml
p:: volume of 10 strips in the counting
chamber, ml
V:: volume of netted or grab sample, liters
S:: volume of counting chamber, ml
5.0 BIOMASS DETERMINAnON
Because natural plankton populations are
composed of many types of organisms (i.e.,
plant, animal, and bacterial), it is difficult to
obtain quantitative values for each of the component
populations. Currently-used indices
include dry and ash-free weight, cell volume, cell
surface area, total carbon, total nitrogen, and
chlorophyll content. The dry and ash-free
weight methods yield data that include the particulate
inorganic materials as well as the plankton.
Cell volume and cell surface area determinations
can be made on individual components
of the population and thus yield data on the
plant, the animal, or the bacterial volume, or
surface area, or both. Chlorophyll determinations
yield data on the phytoplankton.
5.1 Dry and Ash-Free Weight
To reduce the amount of contamination by
dissolved solids, wash the sample with several
volumes of distilled water by centrifugation or
settling. After washing, concentrate the sample
by centrifugation or settling. If possible, take
sufficient sample to provide several aliquots each
having at least 10 mg dry weight. Process at
least two replicate aliquots for each sample.
(Generally, 10 mg dry weight is equivalent to
100 mg wet weight.)