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

BIOLOGICAL METHODS
Equitability "e," as calculated, may range
from a to I except in the unusual situation
where the distribution in the sample is more
equitable than the distribution resulting from
the MacArthur model. Such an eventuality will
result in values of e greater than l, and this
occasionally occurs in samples containing only a
few specimens with several taxa represented.
The estimate of d and e improves with increased
sample size, and samples containing less than
100 specimens should be evaluated with caution,
if at all.
When Wilhm (59) evaluated values calculated
from data that numerous authors had collected
from a variety of polluted and unpolluted
waters, he found that in unpolluted waters d was
generally between 3 and 4, whereas in polluted
water, d was generally less than 1. However,
collected data from southeastern U. S. waters by
EPA biologists has shown that where degradation
is at slight to moderate levels, d lacks the
sensitivity to demonstrate differences. Equitability
e, on the contrary, has been found to be
very sensitive to even slight levels of degradation.
Equitability levels below 0.5 have not been
encountered in southeastern streams known to
be unaffected by oxygen-demanding wastes, and
in such streams, e generally ranges between 0.6
and 0.8. Even slight levels of degradation have
been found to reduce equitability below 0.5 and
generally to a range of 0.0 to 0.3.
Agency biologists are encouraged to calculate
both mean diversity d and equitability e for
samples collected in the course of macroinvertebrate
studies. (If the mean and range of values
found by different sampling methods and under
varying levels and types of pollution are
reported to the Biological Methods Branch,
these data will be included in tabular form in
future revisions of this Section.)
5.2 Qualitative Data
As previously defined, qualitative data result
from samples collected in such a manner that no
estimate of numerical abundance or biomass can
be calculated. The output consists of a list of
taxa collected in the various habitats of the
environment being studied. The numerous
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schemes advanced for the analysis of qualitative
data may be grouped in two categories:
5.2.1 Indicator-organism scheme
For t his technique, individual taxa are
classified on the basis of their tolerance or
intolerance to various levels of putrescible
wastes (4, 5, 30, 42, 48). Taxa are classified
according to their presence or absence in different
environments as determined by Held
studies. Beck (6) reduced data based on the
presence or absence of indicator organisms to a
simple numerical form for ease in presentation.
5.2.2 Reference station methods
Comparative or control station methods
compare the qualitative characteristics of the
fauna in clean water habitats with those of
fauna in habitats subject to stress. Patrick (46)
compared stations on the basis of richness of
species and Wurtz (61) used indicator organisms
in comparing stations.
If adequate background data are available to
an experienced investigator, both of these techniques
can prove quite useful-particularly for
the purpose of demonstrating the effects of
gross to moderate organic contamination on the
macroinvertebrate community. To detect more
subtle changes in the macroinvertebrate community,
collect quantitative data on numbers or
biomass of organisms. Data on the presence of
tolerant and intolerant taxa and richness of
species may be effectively summarized for evaluation
and presentation by means of line graphs,
bar graphs, pie diagrams, histograms, or pictoral
diagrams (27).
The calssification by various authors of representative
macroinvertebrates according to their
tolerance of organic wastes is presented in Table
7. In most cases, the taxonomic nomenclature
used in the table is that of the original authors.
The pollutional classifications of the authors
were arbitrarily placed in three categories ­
tolerant, facultative, and intolerant - defined as
follows:
• Tolerant: Organisms frequently associated
with gross organic contamination and are
generally capable of thriving under
anaerobic conditions.