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

BIOLOGICAL METHODS
Diatom Species Proportional Count
Before preparing the diatom slides, use an
oxidizing agent to digest the gelatinous stalks
and other extracellular organic materials causing
cell clumping. Before the oxidant is added,
however, centrifuge or settle the sample to remove
the formalin.
If centrifugation is preferred, transfer the
sample to a conical tube and centrifuge 10
minutes at 1000 X G. Decant the formalin, resuspend
the sample in 10 ml of distilled water,
and recentrifuge. Decant, take up the sample in
8 ml of 5 percent potassium (or ammonium)
persulfate, and transfer back to the (rinsed)
sample vial.
If the settling method is preferred, follow the
instructions given in the Plankton Section for
removing salt from the diatom concentrate, but
add persulfate or hydrogen peroxide instead of
distilled water. After the formalin is replaced by
the oxidant, heat the sample to 95°C for 30
minutes (do not boil). Cool, remove the oxidant
by centrifugation or settling, and take up the
diatoms in 2 to 3 ml of distilled water. Proceed
with the preparation of the permanent diatom
mount as described in the Plankton Section.
Label the slide with the station location and
inclusive sample dates. Carry out the diatom
strip count as described in the Plankton Section,
except that separated, individual valves (half cell
walls) are tallied as such, and the tally is divided
by two to obtain cell numbers.
3.2.3 Biomass
Cell Volume
See the Plankton Section.
Dry and Ash-free Weight
See the Plankton Section.
Centrifugation, Sedimentation and Displacement
Centrifugation. Place sample in graduated
centrifuge tube and centrifuge for 20 minutes at
1000 X G. Relate the volume in milliliters to the
area sampled.
Sedimentation. Place sample in graduated
cylinder and allow sample to settle at least 24
hours. Relate the volume in milliliters to the
area sampled.
4
Displacement. Use displacement for large
growths of periphyton when excess water can be
readily removed. Once the excess water is removed,
proceed as per Plankton Section; however,
do not pour sample through a No. 20
mesh, nylon bolting cloth.
Chlorophy11
The chlorophyll content of the periphyton is
used to estimate the algal biomass and as an
indicator of the nutrient content (or trophic
status) or toxicity of the water and the taxonomic
composition of the community. Periphyton
growing in surface water relatively free of
organic pollution consists largely of algae, which
contain approximately 1 to 2 percent chlorophyll
a by dry weight. If dissolved or particulate
organic matter is present in high concentrations,
large populations of filamentous bacteria,
stalked protozoa, and other nonchlorophyll
bearing microorganisms develop and the percentage
of chlorophyll a is then reduced. If the
biomass-chlorophyll a relationship is expressed
as a ratio (the autotrophic index), values greater
than 100 may result from organic pollution
(Weber and McFarland, 1969; Weber, 1973).
. Ash-free Wgt (mg/m 2 )
AutotrophiC Index =Chlorophyll a (mg/m2)
To obtain information on the physiological
condition (or health) of the algal periphyton,
measure the amount of pheophytin a, a physiologically
inactive degradation product of chlorophyll
a. This degradation product has an absorption
peak at nearly the same wavelength as chlorophyll
a and, under severe environmental conditions,
may be responsible for most if not all of
the OD 66 3 in the acetone extract. The presence
of relatively large amounts of pheophytin a is an
abnormal condition indicating water quality
degradation. (See the Plankton Section.)
To extract chlorophyll, grind and steep the
periphyton in 90 percent aqueous acetone (see
Plankton Section). Because of the normal seasonal
succession of the algae, the taxonomic
composition and the efficiency of extraction by
steeping change continually during the year.
Although mechanical or other cell disruption
may not increase the recovery of pigment from