Science of Water : Concepts and Applications

Environmental Biomonitoring, Sampling, and Testing 239
sample, is liberated. The amount of iodine is then determined by titration with a standard solution,
usually thiosulfate.
Fortunately for the fi eld biologist, this is the age of miniaturized electronic circuit components
and devices; thus, it is not too diffi cult to obtain portable electronic measuring devices for DO and
temperature that are of quality construction and have better than moderate accuracy. These modern
electronic devices are usually suitable for laboratory and fi eld use. The device may be subjected to
severe abuse in the fi eld; therefore, the instrument must be durable, accurate, and easy to use. Several
quality DO monitors are available commercially.
When using a DO monitor, it is important to calibrate (standardize) the meter prior to use. Calibration
procedures can be found in Standard Methods (latest edition) or in the manufacturer’s instructions
for the meter to be used. Meter calibration usually is accomplished by determining the air
temperature, the DO at saturation for that temperature, and then adjusting the meter so that it reads
the saturation value. After calibration, the monitor is ready for use. As mentioned, all recorded measurements,
including water temperatures and DO readings, should be entered in a fi eld notebook.
Sampling Nets
A variety of sampling nets are available for use in the fi eld. The two-person seine net shown in
Figure 8.7 is 20 ft long × 4 ft deep with 1/8-in. mesh and is utilized to collect a variety of organisms.
Two people, each holding one end and then walking upstream, use it. Small organisms are easily
collected by this method.
Dip nets are used to collect organisms in shallow streams. The Surber sampler (collects macroinvertebrates
stirred up from the bottom; see Figure 8.8) can be used to obtain a quantitative sample
(number of organisms/square feet). It is designed for sampling riffl e areas in steams and rivers up to
a depth of about 450 mm (18 in.). It consists of two folding stainless steel frames set at right angles
to each other. The frame is placed on the bottom, with the net extending downstream. Using your
FIGURE 8.7 Two-person seine net.
FIGURE 8.8 Surber sampler.
Lead sinkers
Cork floaters