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The Rapids at Great Falls
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Traditional stream surveys focus mainly on water chemistry with
little consideration for other ecosystem components. However, the
best way to assess stream health is to consider the quality of the
physical habitat (the places where organisms live), and of the biological
communities that occupy the habitat, as well as water quality. Biomonitoring
is the study of biological communities to evaluate changes in the
environment. Benthic macroinvertebrates are ideal for use in stream
biomonitoring for several reasons:
- They are ubiquitous.
- They are relatively sedentary and long-lived.
- Some species are sensitive to pollution and some are tolerant.
- They are easy to collect and identify.
Biological monitoring can provide information about past and/or
episodic pollution or other environmental stressors. Benthic macroinvertebrates
act as continuous monitors of the water in which they live.
Research on streams in the nontidal portion of the Potomac basin
is hampered by biomonitoring data that exist in varied forms and
cannot easily be compared. The objective of ICPRB’s Basinwide
Assessments program is to improve understanding of the health of
the Potomac watershed by combining benthic macroinvertebrate, habitat,
and water chemistry data collected by the Basin’s member jurisdictions
(Maryland, Pennsylvania, Virginia, West Virginia, and the District
of Columbia). Combining data from diverse sources has historically
been a challenge for scientific investigations, since different
water quality management programs often do not require the same
level or type of effort in sample collection, organism identification,
and data analysis.
Although their monitoring data cannot be directly compared, Potomac
Basin states apply a similar approach to assessing stream health.
This approach requires a stream classification framework to partition
natural variability into groups where ecological expectations are
similar. Groups are usually broad regions defined by geographic
similarities. Measures of stream community health, called metrics,
are combined into a single numeric score called an index. Indices
involve comparisons of reference sites (those that represent the
best attainable conditions in a region) to sites suspected to be
impacted by pollution or other environmental stressors to evaluate
the percent similarity (or difference) in condition.
Since few Potomac streams remain pristine, different jurisdictions
apply different criteria to select reference sites, and apply different
metrics and indices to make comparisons and assess stream health.
To resolve some of these differences, ICPRB is adapting the assessment
framework, using a relational database to store and help analyze
stream data. The modified framework will ultimately provide us with
an overall picture of conditions throughout the Potomac’s nontidal
watershed, as well as establish benchmarks for future assessments. |
