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