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

1.0 INTRODUCTION
The aquatic macroinvertebrates, as discussed
in this section, are animals that are large enough
to be seen by the unaided eye and can be
retained by a U. S. Standard No. 30 sieve (28
meshes per inch, 0.595 mm openings) and live at
least part of their life cycles within or upon
available substrates in a body of water or water
transport system.
Any available substrate may provide suitable
habitat including bottom sediments, submerged
logs, debris, pilings, pipes, conduits, vascular
aquatic plants, filamentous algae, etc.
The major taxonomic groups included in fresh
water are the insects, annelids, molluscs, flatworms,
roundworms, and crustaceans. The
major groups in salt water are the molluscs,
annelids, crustaceans, coelenterates, porifera,
and bryozoans.
Benthic macroinvertebrates can be defined by
location and size but not by position in the
trophic structure since they occupy virtually all
levels. They may be omnivores, carnivores, or
herbivores; and in a well-balanced system, all
three types will likely be present. They include
deposit and detritus feeders, parasites,
scavengers, grazers, and predators.
Species present, distribution, and abundance
of aquatic macroinvertebrates may be subject to
wide seasonal variations. Thus, when conducting
comparative studies, the investigator must be
quite careful to avoid the confounding effects of
these seasonal changes. Seasonal variations are
particularly important in fresh-water habitats
dominated by aquatic insects having several life
stages, not all of which are aquatic.
The macroinvertebrates are important
members of the food web, and their well-being is
reflected in the well-being of the higher forms
such as fish. Many invertebrates, such as the
marine and fresh-water shellfish, are important
commercial and recreational species. Some, such
as mosquitos, black flies, biting midges, and
Asiatic clams, are of considerable public health
significance or are simple pests; and many forms
are important for digesting organic material and
recycling nutrients.
MACROINVERTEBRATES
A community of macroinvertebrates in an
aquatic ecosystem is very sensitive to stress, and
thus its characteristics serve as a useful tool for
detecting environmental perturbations resulting
from introduced contaminants. Because of the
limited mobility of benthic organisms and their
relatively long life span, their characteristics are
a function of conditions during the recent past,
including reactions to infrequently discharged
wastes that would be difficult to detect by
periodic chemical sampling.
Also, because of the phenomenon of
"biological magnification" and relatively longterm
retention of contaminants by benthic
organisms, contaminants such as pesticides,
radioactive materials, and metals, which are only
periodically discharged or which are present at
un detectable levels in the water, may be
detected by chemical analyses of selected components
of the macroinvertebrate fauna.
In pollution-oriented studies of macroinvertebrate
communities, there are basically two
a pproaches-quantitative and qualitative-that
may be utilized singly or in combination.
Because of the basic nature of this decision, the
section of this manual relating to sampling
methods and data evaluation of macroinvertebrates
is arranged on the basis of whether a
quantitative or qualitative approach is used.
Ideally, the design of macroinvertebrate
studies should be based upon study goals or
objectives; however, the ideal must frequently
be tempered by the realities of available
resources, time limitations imposed on the
study, and the characteristics of the habitat to
be studied. To aid in selecting the most
advantageous sampling method, sample sites,
and data evaluation, the reader of this section
should be familiar with the material in the
"Introduction" of this manual, particularly
those portions outlining and discussing requirements
of the various types of field studies in
which an investigator may become involved.
To supplement the material contained in this
manual, a number of basic references should be
available to investigators of the benthic community,
particularly to those engaged in water