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What Is This Indicator, and Why Is It Important?
This indicator reports on “biological integrity”
in streams in urban and suburban areas. Biological integrity
is a measure of the degree to which the suite of fish and
bottom-dwelling (or benthic) animals (including insects, worms,
mollusks, and crustaceans) resembles what one might find in
a relatively undisturbed stream in the same region. Tests
assess the number of different species, number and condition
of individuals, and food chain interactions. High scores indicate
close resemblance to “reference” or undisturbed
conditions, and low scores indicate significant deviation
from them. (See also Status
of Freshwater Animal Communities)
Undisturbed streams in a particular region have a relatively
predictable set of fish and bottom-dwelling animals, in predictable
proportions. The composition and condition of these biological
communities may be altered, often as a result of development
in the stream’s watershed. Sources of degradation include
contaminated runoff from streets, driveways, lawns, golf courses,
and the like, increased stream temperature caused by runoff
that is warmed as it flows over paved surfaces, and channelizing
or other modifications of the streambed. Some streams are
so modified that, for example, both the number of species
and the number of individuals are very low when compared to
undisturbed areas, and many of those that remain are diseased
or otherwise damaged. Ecosystems that are “healthy,”
or show high integrity, are more likely to withstand natural
and man-made stresses.
Why Can't This Indicator Be Reported at This Time?
The tests of biological integrity now in use must
be tailored to ensure that each stream is compared with an
appropriate reference from within the same region, but outside
of the urban/suburban area. Only a handful of states regularly
conduct quantitative tests of condition of fish or bottom-dwelling
animal communities, and these are not specific to urban streams.
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