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

BIOLOGICAL METHODS
pollution studies. These include Standard
Methods (2), Welch (57), Mackenthun (37),
Kittrell (29), Hynes (26), and Buchanan and
Sommers (9).
2.0 SELECTION OF SAMPLE SITES
As discussed and defined more fully in the
section on biometrics, sample sites may be
selected systematically or by various randomization
procedures.
2.1 Systematic Sampling
Unless the data are to be utilized for quantitative
evaluations, some type of systematic
sampling is generally employed for synoptic
surveys and reconnaissance studies. Line
transects established at discrete intervals across a
river or stream and sampled at quarter points or
more frequent intervals are a form of systematic
sampling and serve as an excellent means of
delimiting and mapping the habitat types. In
lakes, reservoirs, and estuaries, transects may be
established along the short or long axis or may
radiate out from a pollution source. If a random
start point is used for selecting sampling sites
along the transects, the data may be amenable to
quantitative evaluation (see Biometrics Section).
As will be discussed, however, the confounding
effects of changes in physical characteristics of
the environment along the transect must be fully
recognized and accounted for.
In another form of systematic sampling, the
investigator, using a variety of gear, consciously
selects and intensively samples all recognizable
habitat types. As previously mentioned, this
form of sample site selection is useful for
synoptic surveys and for comparative studies
where qualitative comparisons are being made.
2.2 Random Sampling
For conducting quantitative studies, where a
measure of precision must be obtained, some
type of randomization procedure must be
employed in selecting sampling sites. This selection
may be carried out on the whole of the area
under study (simple random sampling), or the
randomization procedure may be conducted
independently on selected strata (stratified
random sampling). Because the characteristics of
2
macroinvertebrate communities are so closely
related to physical factors such as substrate
type, current velocity, depth, and salinity, a
design using simple random sampling is seldom
meaningful. Therefore, the investigator should
stratify the habitat on the basis of known
physical habitat differences and collect samples
by the random grid technique within each
habitat type.
As alluded to above, and regardless of the
method of sample site selection, the biologist
must consider and account for those natural
environmental variations that may affect the
distribution of organisms. Among the more
important natural environmental variables in
fresh-water habitats are substrate type, current
velocity, and depth. In estuaries, the salinity
gradient is an additional variable that must be
accounted for.
2.3 Measurement of Abiotic Factors
2.3.1 Substrate
Substrate is one of the most important factors
controlling the characteristics of the community
of aquatic macroinvertebrates found at a given
location in a body of water (49). Over a period
of time, the natural substrates may be greatly
altered by the discharge of particulate mineral or
organic matter, and the location and expanse of
various substrate types (silt, sand, gravel, etc.)
may change because of normal variations in
hydrolic factors such as current velocity and
stream flow. The biologist, therefore, must be
cognizant of changes in the nature and
properties of the substrate which may provide
clues on the quality and quantity of pollutants
and consider factors which affect the normal
distribution of the benthic fauna.
Where the pollutant has a direct effect on the
characteristics of the substrate, the effects of
changes in water quality may be inseparable
from the effects of changes in the substrate. In
cases where substrate deterioration has occurred,
faunal effects may be so obvious that extensive
sampling may not be required, and special attention
should be given to the physical and/or
chemical characterization of the deposits.
In conducting synoptic surveys or other types
of qualitative studies and taking into account