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

BIOLOGICAL METHODS
Calculate the chlorophyll a and pheophytin a
as follows:
Chlorophyll a (mg/m 3 ) =26.7 (663b -663 a ) X E
VXL
Pheophytin a (mg/m 3 ) = 26.7 (1.7 X 663a - 663b) X E
VXL
where 663b is the I-em corrected 00 663 before
acidification; 663a is the 00 663 after acidification;
E the volume of acetone used for the
extraction (m}); V the volume of water filtered
(liters); and L the path length of the cuvette
(em).
5.3 Cell Volume
5.3.1 Microscopic (algae and bacteria)
Concentrate an aliquot of sample by settling
or centrifugation, and examine wet at a 1000X
magnification with a microscope equipped with
a calibrated ocular micrometer. Higher magnification
may be necessary for small algae and the
bacteria. Make optical measurements and
determine the volume of 20 representative
individuals of each major species. Determine the
average volume (cubic microns), and multiply by
number of organisms per milliliter.
5.3.2 Displacement (zooplankton)
Separate sample from preservative by pouring
through a piece of No. 20 mesh nylon bolting
cloth placed in the bottom of a small glass
funnel. To hasten evaporation, wash sample with
a small amount of 50 percent ethanol to remove
excess interstitial fluid and place on a piece of
filter or blotting paper. Place the drained plankton
in a 25-, 50-, or 100-ml (depending on
sample size) graduated cylinder, and add a
known volume of water from a burette. Read
the water level in the graduated cylinder. The
difference between the volume of the zooplankton
plus the added water and the volume of the
water alone is the displacement volume and,
therefore, the volume of the total amount of
zooplankton in the sample.
5.4 Cell Surface Area of Phytoplankton
Measure the dimensions of several representative
individuals of each major species with a
16
microscope. Assume the cells to be spherical
cylindrical, rectangular, etc., and from the linear
dimensions, compute the average surface area
(p.2) per species. Multiply by the number of
organisms per milliliter (Welch, 1948, lists
mathematical formulas for computing surface
area).
6.0 PHYTOPLANKTON PRODUCTIVITY
Phytoplankton productivity measurements
indicate the rate of uptake of inorganic carbon
by phytoplankton during photosynthesis and are
useful in determining the effects of pollutants
and nutrients on the aquatic community.
Several different methods have been used to
measure phytoplankton productivity. Diurnal
curve techniques, involving pH and dissolved
oxygen measurements, have been used in natural
aquatic communities by a number of investigators.
Westlake, Owens, and TaIling (1969)
present an excellent discussion concerning the
limitations, advantages, and disadvantages of
diurnal curve techniques as applied to nonisolated
natural communities. The oxygen
method of Gaarder and Gran (1927) and the
carbon-14 method of Steeman-Neilson (1952)
are techniques for measuring in situ phytoplankton
productivity. TaIling and Fogg (1959)
discussed the relationship between the oxygen
and carbon-14 methods, and the limitations of
both methods. A number of physiological
factors must be considered in the interpretation
of the carbon-14 method for measurement of
phytoplankton productivity. Specialized applications
of the carbon-14 method include bioassay
of nutrient limiting factors and measurement
of the potential for algal growth.
The carbon-14 method and the oxygen
method have the widest use, and the following
procedures are presented for the in situ field
measurement of inorganic carbon uptake by
these methods.
6.1 Oxygen Method
General directions for the oxygen method are
found in: Standard Methods for the Examination
of Water and Wastewater, 13th Edition,
pp. 738-739 and 750-751.