Science of Water : Concepts and Applications

220 The Science of Water: Concepts and Applications
sensitive to pollution while others are more tolerant. However, like toxicity testing, biomonitoring
does not tell you why animals are present or absent. As mentioned, benthic macroinvertebrates are
excellent indicators for several reasons:
1. Biological communities refl ect overall ecological integrity (i.e., chemical, physical, and
biological integrity). Therefore, biosurvey results directly assess the status of a water body
relative to the primary goal of the Clean Water Act (CWA).
2. Biological communities integrate the effects of different stressors and thus provide a broad
measure of their aggregate impact.
3. Because they are ubiquitous, communities integrate the stressors over time and provide an
ecological measure of fl uctuating environmental conditions.
4. Routine monitoring of biological communities can be relatively inexpensive because they
are easy to collect and identify.
5. The status of biological comminutes is of direct interest to the public as a measure of a
particular environment.
6. Where criteria for specifi c ambient impacts do not exist (e.g., nonpoint-sources that degrade
habitats), biological communities may be the only practical means of evaluation.
7. They can be used to assess nonchemical impacts to the aquatic habitat, such as by thermal
pollution, excessive sediment loading (siltation), or eutrophication.
Benthic macroinvertebrates act as continuous monitors of the water they live in. Unlike chemical
monitoring, which provides information about water quality at the time of measurement (a snapshot),
biological monitoring can provide information about past and episodic pollution (a videotape).
This concept is analogous to miners who took canaries into deep mines with them to test for air
quality. If the canary died, the miners knew the air was bad and they had to leave the mine. Biomonitoring
a water body ecosystem uses the same theoretical approach. Aquatic macroinvertebrates are
subject to pollutants in the water body. Consequently, the health of the organisms refl ects the quality
of the water they live in. If the pollution levels reach a critical concentration, certain organisms
will migrate away, fail to reproduce, or die, eventually leading to the disappearance of those species
at the polluted site. Normally, these organisms will return if conditions improve in the system
(Bly and Smith, 1994).
Biomonitoring (and the related term, bioassessment) surveys are conducted before and after
an anticipated impact to determine the effect of the activity on the water body habitat. Moreover,
surveys are performed periodically to monitor water body habitats and watch for unanticipated
impacts. Finally, biomonitoring surveys are designed to reference conditions or to set biocriteria
(serve as monitoring thresholds to signal future impacts, regulatory actions, etc.) for determining
that an impact has occurred (Camann, 1996).
Biological monitoring cannot replace chemical monitoring, toxicity testing, and other standard
environmental measurements. Each of these tools provides the analyst with specifi c information
available only through its respective methodology.
√ Note: The primary justifi cation for bioassessment and monitoring is that degradation of water
body habitats affects the biota using those habitats, and, therefore, the living organisms themselves
provide the most direct means of assessing real environmental impacts.
BIOTIC INDEX (STREAMS)
Certain common aquatic organisms, by indicating the extent of oxygenation of a stream, may be
regarded as indicators of the intensity of pollution from organic waste. The responses of aquatic
organisms in water bodies to large quantities of organic wastes are well documented. They occur
in a predictable cyclical manner. For example, upstream from the discharge point, a stream can