States and Tribes - Water Quality Criteria and Standards
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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.