Water Quality Criteria and Standards
The water quality standards program, as envisioned in section 303(c)
of the Clean Water Act (CWA), is a joint effort between the states
and USEPA. The states have primary responsibility for setting, reviewing,
revising, and enforcing water quality standards. USEPA develops
regulations, policies, and guidance to help states implement the
program and oversees states' activities to ensure that state-adopted
standards are consistent with the requirements of the CWA and that
water quality standards regulations (40 CFR Part 131) are met; USEPA
has authority to review and approve or disapprove state standards
and, where necessary, to promulgate federal water quality standards.
A water quality standard defines the water quality goals of a waterbody,
or a portion thereof, by designating the use or uses to be made
of the water, setting criteria necessary to protect those uses,
and preventing degradation of water quality through antidegradation
provisions. States adopt water quality standards to protect public
health or welfare, enhance the quality of water, and protect biological
integrity.
Environmental stressors can be chemical, physical or biological
in nature, and likewise can impact the chemical, physical, and biological
characteristics of an aquatic ecosystem. For example, the impact
of a chemical stressor might be observed in impaired functioning
or loss of a sensitive species and a change in community structure.
The impact of a biological stressor, such as an introduced species,
can result in a change in community structure through competition,
predation, etc. Ultimately, the number or intensity of all stressors
within an ecosystem will be evidenced by a change in the condition
and function of the biotic community. The interactions among chemical,
physical, and biological stressors and their compounding impacts
emphasize the need to directly detect and assess actual water quality
impairments of the biota.
Sections 303 and 304 of the CWA require states to protect biological
integrity as part of their water quality standards. This can be
accomplished, in part, through the development and use of biological
criteria. As part of a state or tribal water quality standards program,
biological criteria can provide scientifically sound and detailed
descriptions of the designated aquatic life use for a specific waterbody
or segment. They fulfill an important assessment function in water
quality-based programs by establishing the biological benchmarks
for (1) directly measuring the condition of the aquatic biota, (2)
determining water quality goals and setting priorities, and (3)
evaluating the effectiveness of implemented controls and management
actions.
The challenge of evaluating effects from ecological stressors will
best be met when the condition of the biota within an ecosystem
can be assessed directly. Biological criteria for aquatic life will
help meet this need by allowing direct assessment of the condition
of the biota that live either part or all of their lives in aquatic
systems. These criteria (narrative or numeric) describe the expected
biological condition of an aquatic community. They can be used as
benchmarks to identify biological impairments and to help define
ecosystem goals and endpoints. Biological criteria supplement traditional
measurements (for example, as backup for hard-to-detect chemical
problems) and will be particularly useful in assessing impairment
due to non-point source pollution and non-chemical (e.g., physical
and biological) stressors.
Thus, biological criteria fulfill a function missing from USEPA's
traditionally chemical-oriented approach to pollution control and
abatement (USEPA. 1996. Biological Criteria: Technical Guidance
for Streams and Small Rivers, EPA 822-B-96-001. U.S. Environmental
Protection Agency, Office of Water, Washington, D.C.).
Biological criteria can also be used to refine the aquatic life
use classifications for a state. Each state develops its own designated
use classification system based on the generic uses cited in the
CWA, including protection and propagation of fish, shellfish, and
wildlife. States frequently develop subcategories to refine and
clarify designated use classes when several surface waters with
distinct characteristics fit within the same use class or when waters
do not fit well into any category; for example, cold-water versus
warm-water habitat. As data are collected from biosurveys to develop
a biological criteria program, analysis may reveal unique and consistent
differences between aquatic communities that inhabit different waters
with the same designated use. Therefore, measurable biological attributes
can be used to refine aquatic life use or to separate one class
into two or more subclasses.
How to Adopt Biological Criteria into Water
Quality Standards
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