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Tiered aquatic life use (TALU) framework

West Branch Little Knife River, Badger Run, Judicial Ditch 7

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Minnesota is revising its water quality standards (Minn. Rule Chapter 7050) to incorporate a tiered aquatic life use (TALU) framework for rivers and streams. The TALU framework represents a significant revision to the water quality standards of the state's aquatic life use classification. The framework builds upon existing water quality standards with a goal of improving how water resources are monitored and managed. Additionally, these changes advance the ability to identify “stressors” and develop effective mechanisms to improve and maintain the condition of waters in the state of Minnesota. The initial rulemaking to adopt  TALU will affect Class 2 (Aquatic Life) standards.

The adoption of a Minnesota TALU framework achieves several goals:

  • Biological standards: Incorporated into water quality standards, they provide a more direct method to measure and protect biological health and identify water quality problems that chemical measurements alone might miss.
  • High quality water resources: TALU provides a mechanism to identify and protect high quality water resources.
  • Modified water resources: TALU provides a mechanism to classify and assess modified water resources. These include channelized streams and ditches.
  • Stressor identification: Improve our ability to accurately identify the wide diversity of stressors that impact Minnesota's water resources.

Achieving these goals through the TALU framework will enhance the protection and maintenance of the biological, chemical and physical integrity of water resources in the state.


Why does Minnesota need a tiered aquatic life use framework?

The Clean Water Act (CWA) requires states to assign beneficial uses to waterbodies and to develop water quality criteria to protect those uses. Most surface waters in Minnesota are protected for aquatic life and recreation.Traditionally, aquatic life has been protected through the application of water chemistry based standards. However, the use of only chemical and physical water quality standards to protect aquatic life may provide an incomplete assessment. Measuring one, two or even a handful of chemical and physical parameters as a surrogate for protection of aquatic life can miss impairments.The TALU framework relies on a combination of biological, physical, and chemical monitoring to measure the attainment of aquatic life goals directly. The TALU framework also produces a systematic process with a monitoring and assessment program that collects the right kinds of data which can be used at the same scale that management is being applied. As a result, monitoring and assessment work in parallel with water quality standards to develop effective standards that result in the protection of designated uses.

What is the TALU framework being considered?

The TALU framework will move Minnesota's aquatic life standards from a “one-size-fits-all” approach to one that protects appropriately classified waters based on their biological potential. This means that high quality or Exceptional Use waters will be given additional protection to ensure that the condition of these habitats are maintained. The majority of streams and rivers will continue to be protected as General Use or good quality waters. Some waters that are impacted by legacy or historical impacts (for example ditches) could be eligible for a lower goal if it is demonstrated that the biology cannot attain at least the General Use. Class 2 waters meeting Exceptional Use biological goals can be redesignated as an Exceptional Use because the biology has demonstrated that the use is attainable. Similarly waters meeting the General Use goal would be designated General Use. However, if the General Use goals are not met, then additional analyses would need to be performed to determine the attainable use. Specifically, a Use Attainability Analysis (UAA) would need to be performed to determine if the habitat is limiting the biology and what is the cause of the poor habitat. Biological communities that are limited by habitat that are a result of legal activities (for example ditch maintenance) could then be redesignated Modified Use.

TALU Use Framework

Biological goals for TALU are based on a scientific model called the biological condition gradient (BCG) and reference waters. The BCG model describes how biological communities change with increasing levels of stress. The BCG is based on the concept that waterbodies receiving higher levels of stress have biological communities with lower condition compared to waterbodies receiving lower levels of stress (see Figure 1 below). The BCG provides a common framework to interpret changes in biological condition regardless of geography or water resource type. It permits a more accurate determination and classification of Minnesota's aquatic resources which improves the ability to make well-informed decisions on aquatic life designations. The BCG is supported by reference condition sites. These reference condition sites are from waters that are minimally or least disturbed and therefore serve as a benchmark for assessment. Goals or biological criteria developed using both the BCG and reference sites largely agree and serve to strengthen these goals.

Figure 1. Biological condition gradient

Biological Condition Gradient


What are the major goals/outcomes of the TALU framework

Biological standards. Water quality standards in Minnesota are currently based on chemical and physical criteria such as dissolved oxygen and pH. These criteria do not directly measure the health or condition of biological communities which include fishes, insects, mussels, aquatic plants and algae. Although chemical and physical measures can tell us a lot about water quality, these criteria are essentially surrogates for a direct measure of the biological community. This can be problematic due to the large number and diversity of the stressors that impact biological communities which include chemicals, reduced oxygen, sedimentation, increased temperature, and habitat degradation (see figure 2 below). As a result, the monitoring of chemical and physical parameters for all potential stressors can become too cumbersome to be practical. Rather than measuring the wide variety of stressors, biological communities can be monitored as they are a direct measure of the response of the biota to a wide range of physical and chemical stressors. In other words, their condition is a reflection of all the impacts of multiple stressors over time. Chemical standards have been, and will remain, an important aspect of our protection measures. However, the addition of biological monitoring and biological standards will complement them and will result in refinement of chemical criteria.


Figure 2. Five major factors that determine the integrity of aquatic resources

Diagram of the The Five Major Factors that Determine the Integrity of Aquatic Resources

High quality water resources. Another limitation of Minnesota's current water quality framework is that high quality resources are often under protected. At present there is a framework to protect the degradation of high quality waters called antidegradation, but there are still elements of Minnesota's antidegradation provisions in rule that can allow considerable degradation of these waters without violating the CWA. TALU establishes a higher tier of use to protect these high quality waters. Once a water body has been established as meeting the requirements of a high quality water resource, the resource needs to be protected to maintain that status. The concept of protecting the “existing” use of a waterbody is one of the most important tenets of the CWA.

Modified or limited water resources. There are water resources in this state that will not in the near future meet the CWA interim goals due to legacy impacts. These legacy impacts are those impacts that preceded the CWA. This includes streams under drainage maintenance or other irreversible hydromodification that preclude attainment of goals. For example, channelized streams and ditches would be included in this category. TALU provides a mechanism to monitor and set realistic expectations for waters that are unlikely to meet goals due to legacy impacts. The expectations fully protect the existing uses of each waterbody and recognize their historical and current site specific context. This element of TALU allows for the establishment of realistic expectations for waterbodies that have multiple and well established uses.

Stressor Identification: When biological communities are determined to not be attaining General Use goals, the MPCA will need to have the tools and knowledge to determine in a timely manner if a lower use is appropriate and if the water body does not attain the designated use, what stressors are resulting in nonattainment. TALU incorporates the concept of pollution into assessments of condition and provides an opportunity to address the key stressors that are the most determinant of biological condition. In doing so, TALU allows assessment and water quality management efforts to focus on the correct problems.

Some other goals/benefits of TALU adoption include:

  • Monitoring of incremental improvements in water quality. This allows entities working to improve water quality to document and show progress toward a goal.
  • TALU helps guide development and modification of water quality standards to produce improved standards.
  • TALU merges the design and practice of monitoring and assessment with the development and implementation of water quality standards.


The MPCA is beginning the process of amending the state water quality standards to incorporate TALU. At a minimum this rulemaking will make changes to Minnesota Rules ch. 7050 and may also affect some aspects of Minnesota Rules chs. 7052 and 7053. Information about the rulemaking will be provided in the files below as the rulemaking process continues.

Background documents/technical support documents

Rulemaking documents

Schedule/public participation opportunities

Stage of rulemaking



Request for Comments

Request for Comments published August 25, 2014.Close of Comment period, 4:30 on October 17, 2014

Drafting of rule language/SONAR

In process

Pre-proposal public engagement period


Public Comment Period/Notice Of Hearing


Post-Comment Period/Administrative Law Judge Review


Adoption of Rules


U.S. EPA Review and Approval


MPCA contact information

Questions about TALU/ water standards:

Will Bouchard

Questions about the status of the rulemaking, public meetings/hearings or how to submit comments:

Carol Nankivel

Last modified on August 25, 2015 09:49

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