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

sampling is usually sufficient. In deeper areas,
take samples at regular intervals with depth. If
only phytoplankton are to be examined, samples
may be taken at three depths, evenly spaced
from the surface to the thermocline. When collecting
zooplankton, however, sample at 1meter
intervals from the surface to the lake
bottom.
Because many factors influence the nature
and distribution of plankton in estuaries, intensive
sampling is necessary. Here, marine and
freshwater plankton may be found along with
brackish-water organisms that are neither strictly
marine nor strictly freshwater inhabitants. In
addition to the influences of the thermocline
and light penetration on plankton depth distribution,
the layering of waters of different salinities
may inhibit the complete mixing of
freshwater plankton with marine forms. In
estuaries with extreme tides, the dimensions of
these layers may change considerably during the
course of the tidal cycle. However, the natural
buoyancy of the plankton generally facilitates
the mixing of forms. Estuarine plankton should
be sampled at regular intervals from the surface
to the bottom three or four times during one or
more tidal cycles.
In deep marine waters or lakes, collect plankton
samples at 3- to 6-meter intervals throughout
the euphotic zone (it is neither practical nor
profitable to sample the entire water column in
very deep waters). The limits of sampling depth
in these waters may be an arbitrary depth below
the thermocline or the euphotic zone, or both.
Perform tow or net sampling at 90° to the wind
direction.
2.1.5 Field notes
Keep a record book containing all information
written on the sample label, plus pertinent
additional notes. These additional notes may
include, but need not be restricted to:
• Weather information - especially direction
and intensity of wind
• Cloud cover
• Water surface condition - smooth? Is
plankton clumping at surface?
• Water color and turbidity
3
PLANKTON COLLECTION
• Total depth at station
• A list of all types of samples taken at
station.
• General descriptive information (e.g.,
direction, distance, and description of
effluents in the vicinity). Sampling
stations should be plotted on a map.
2.1.6 Sample labelling
Both labels and marker should be water proof
(a soft-lead pencil is recommended). Insert the
labels into sample containers immediately as
plankton samples are collected. Record the
following information on all labels:
• Location
name of river, lake, etc.
distance and direction to nearest city
state and county
river mile, latitude, and longitude, or
other description
• Date and time
• Depth
• Type of sample (e.g., grab, vertical plankton
net haul, etc.)
• Sample volume, tow length
• Preservatives used and concentration
• Name of collector
2.2 Phytoplankton
2.2.1 Sampling equipment
The type of samping equipment used is highly
dependent upon where and how the sample is
being taken (i.e., from a small lake, large deep
lake, small stream, large stream, from the shore,
from a bridge, from a small boat, or from a large
boat) and how it is to be used.
The cylindrical type of sampler with stoppers
that leave the ends open to allow free passage of
water through the cylinder while it's being
lowered is recommended. A messenger is released
at the desired depth to close the stoppers
in the ends. The Kemmerer, Juday, and Van
Dorn samplers have such a design and can be
obtained in a variety of sizes and materials. Use
only nonmetallic samplers when metal analysis,
algal assays, or primary productivity measurements
are being performed. In shallow waters
and when surface samples are desired, the