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

BIOLOGICAL METHODS
sampler can be held in a horizontal position and
operated manually. For sampling in deep waters,
the Nansen reversing water bottle is often used
and a boat equipped with a winch is desirable.
Take caution when sampling from bridges with a
Kemmerer type water bottle; if the messenger is
dropped from the height of a bridge, it can
batter and destroy the triggering device. To
avoid this, support a messenger a few feet above
the sampler by an attached string and drop it
when the sampler is in place.
Net collection of phytoplankton is not
recommended for quantitative work. Nannoplankton
and even larger algae, such as some
pennate diatoms, are thin enough to pass
through the meshes of the net if oriented
properly. Using a pump also presents problems:
when the water is stratified, the tubing must be
flushed between samplings and delicate algae
may be harmed.
2.2.2 Sample volume
No fixed rule can be followed concerning the
volume of sample to be taken - sampling personnel
must use their own judgment. The volume
of the sample needed depends on the
numbers and kinds of analyses to be carried out,
e.g., cell counts, chlorophyll, dry weight. When
phytoplankton densities are less than 500 per
mI, approximately 6 liters of sample are required
for Sedgwick-Rafter and diatom species proportional
counts. In most cases, a 1- to 2-titer
sample will suffice for more productive waters.
2.2.3 Sample preservation
Biologists use a variety of preservatives, and
each has advantages. If samples are to be stored
for more than 1 year, the preferred preservative
is formalin (40 percent formaldehyde = 100 percent
formalin), which has been neutralized with
sodium tetraborate (pH 7.0 to 7.3). Five milliliters
of the neutralized formalin are added for
each 100 ml of sample. This preservative will
cause many flagellated forms to lose flagella.
Adding saturated cupric sulfate solution to the
preserved samples maintains the green color of
phytoplankton samples and aids in distinguishing
phytoplankton from detritus. One milliliter
of the saturated solution per liter of sample
is adequate. Adding detergent solution prevents
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clumping of settled organisms. One part of
surgical detergent to five parts of water makes a
convenient stock solution. Add 5 ml of stock
solution per liter of sample. Do not use detergent
when diatom slides are to be made.
Merthiolate is less desirable as a preservative,
but offers the advantage of staining cell parts
and simplifying identification. It also causes
some of the algae, such as blue-greens, to lose
gas from their vacuoles and, therefore, enhances
settling. Samples preserved with merthiolate are
not sterile, and should not be stored for more
than 1 year. After that time formalin should be
used. Merthiolate solution is prepared by dissolving
the following in I liter of distilled water.
• 1.0 gram of merthiolate (sodium ethylmercury
thiosalicylate).
• 1.0 ml of aqueous saturated iodinepotassium
iodide solution prepared by
dissolving 40 grams of iodine and 60
grams of potassium iodide in I liter of
distilled water.
• 1.5 gram of Borax (sodium borate)
Dissolve each of the components separately in
approximately 300 ml of distilled water, combine,
and make up to 1 liter with distilled water.
Add the resulting stock solution to samples to
give a final concentration (VIV) of 36 mg/liter
(Le., 37.3 ml added to I liter of sample).
2.3 Zooplankton
2.3.1 Sampling equipment
Zooplankton analyses require larger samples
than those needed for phytoplankton analyses.
Collect quantitative samples with a messengeroperated
water bottle, plankton trap, or metered
plankton net. Obtain semi-quantitative samples
by filtering surface water samples through nylon
netting or by towing an unmetered plankton net
through the water. In moderately and highly
productive waters, a 6-liter water sample is
usually sufficient. In oligotrophic, estuarine, and
coastal waters, remove zooplankters from several
hundred liters of the waters being sampled with
the use of towed nets. Take duplicate samples if
chemical analyses are desired.