United States
Environmental Protection
Agency
Office of Water
4304
EPA-822-F-01-010
December 2001
FACT SHEET
4^ EPA ECOREGIONAL NUTRIENT CRITERIA
Summary
The U.S. Environmental Protection Agency (EPA) is publishing nine new nutrient water quality
criteria documents for lakes and reservoirs, and rivers and streams within specific geographic
regions (ecoregions) of the United States. These recommended section 304(a) water quality
criteria for nutrients were developed with the aim of reducing and preventing eutrophication on a
national scale. Each document presents recommended criteria for causal parameters (total
phosphorus and total nitrogen) and response variables (chlorophyll a and some form of water
clarity, i.e., turbidity or Secchi depth). This information is intended as a starting point for states,
authorized tribes and others to develop more refined nutrient criteria, as appropriate, using EPA
waterbody-specific technical guidance manuals and other scientifically defensible approaches.
EPA will work with states and authorized tribes as they adopt water quality criteria for nutrients into
their water quality standards.
Background
EPA is publishing nine new ecoregional
nutrient criteria documents to support the
development of state and tribal nutrient
criteria for two waterbody types - lakes and
reservoirs, and rivers and streams. These
nine documents cover four nutrient
ecoregions for lakes and reservoirs and five
nutrient ecoregions for rivers and streams.
They collectively present approximately
160 individual water quality criteria for
nutrients. (There are a total of fourteen
nutrient ecoregions.) EPA issued
seventeen ecoregional nutrient criteria in
January 2000. EPA's nutrient website
(www.epa.gov/ost/standards/nutrient.html)
presents the geographic coverage
and the recommended nutrient water
quality criteria for each nutrient ecoregion.
Why is EPA publishing Ecoregional
Nutrient Criteria?
The national goals of the Clean Water Act
are to achieve, wherever attainable, water
quality which provides for the protection
and propagation offish, shellfish, and
wildlife and recreation in and on the water.
As part of state and tribal water quality
standards, the Clean Water Act requires
states and authorized tribes to specify
designated uses for their waters in
consideration of the these goals, and to adopt
water quality criteria that protect those
designated uses. To help states and tribes,
EPA develops and publishes national criteria
guidance and information. This information
presents the latest scientific knowledge on the
effects of pollutants on biological community
diversity, productivity, and stability, including
information on the factors affecting rates of
eutrophication (excess amounts of nutrients
that stimulate undesirable plant growth) for
receiving waters.
Overview of the Problem
Eutrophication of United States surface waters
is a long standing problem. As much as half of
the Nation's waters surveyed by states and
tribes do not adequately support aquatic life
because of excess nutrients. Nitrogen and
phosphorus are the primary causes of
eutrophication and resulting algal blooms.
Chronic symptoms of overenrichment include
low dissolved oxygen, fish kills, cloudy murky
water, and depletion of desirable flora and
fauna. Nutrient levels that lead to these
problems vary from one region of the country to
another due to geographical variations in
geology, climate and soil types. In order to be
most effective, therefore, state and tribal water
quality criteria need to take into account
ecoregional variations.
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What are ecoregional nutrient criteria
and how should they be used?
Nutrient criteria are numerical values for
both causative (phosphorus and nitrogen)
and response (chlorophyll a and turbidity)
variables associated with the prevention
and assessment of eutrophic conditions.
EPA's recommended ecoregional nutrient
criteria represent conditions of surface
waters that have minimal impacts caused
by human activities. Therefore, when a
state or tribe applies these criteria, the
waters are protected from the harmful
consequences of nutrient overenrichment.
These recommended water quality criteria
are suggested baselines which states and
tribes should refine to help identify problem
areas, serve as a basis for state and tribal
water quality criteria for nutrients, and
evaluate relative success in reducing
eutrophication.
What are the activities
related to these criteria documents?
EPA published a Notice of Availability in the
Federal Register to solicit scientific views
on the criteria documents. EPA will review
and consider new information submitted by
the public on significant scientific issues
and site-specific data. EPA will also forward
pertinent data submitted by the public to
the appropriate Region to help develop
more refined local criteria.
The criteria have been through external
peer review, and a summary of these
comments are available on the Nutrient
website
(www.epa.gov/ost/standards/nutrient.html)
EPA intends to complete publication of
ecoregional nutrient criteria documents for
lakes and reservoirs, rivers and streams,
and wetlands within the remaining
ecoregions, as well as estuarine and
coastal waters in the near future.
or subregion-specific conditions. EPA expects
these more precise numerical levels to be
developed on a smaller geographic scale than
the ecoregional values presented in the nutrient
water quality criteria documents. States and
tribes may also develop criteria using other
scientifically defensible methods and
appropriate water quality data or simply adopt
EPA's recommended water quality criteria in
their water quality standards. EPA expects
states and tribes to prepare a plan for adopting
nutrient criteria and to adopt new or revised
nutrient criteria into their water quality
standards.
Will these criteria be revised in the future?
After we review the submitted significant
scientific information, EPA may publish either
revised criteria or a notice informing the public
that it does not intend to revise the documents
presently. EPA will, however, update the
criteria as new scientific information becomes
available.
How do I obtain a copy of the documents?
You can get copies of the complete set of nine
ecoregional criteria documents, or a specific
ecoregional criteria document from EPA's
National Service Center for Environmental
Publications (NSCEP), 11029 Kenwood Road,
Cincinnati, OH 45242; (513) 489-8190 or toll
free (800) 490-9198. You can also get copies
by contacting the Water Resource Center at
(202) 260-7786. Alternatively, consult EPA's
nutrient website at
www.epa.gov/ost/standards/nutrient.html for
downloads. EPA's waterbody-specific technical
guidance manuals, which present the Agency's
recommended nutrient criteria derivation
methodology, are also available at this website.
What are EPA's expectations for these
criteria?
EPA expects that states and tribes will use
these nine ecoregional nutrient criteria
documents as starting points to identify
more precise numeric levels for nutrient
parameters needed to protect aquatic life,
recreational, or other uses on site-specific
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