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Use of Level IV Ecoregion Reference Stream Data to Develop Regionalized Water Quality Criteria

Gregory M. Denton

Division of Water Pollution Control
Tennessee Department of Environment and Conservation
7th Floor, L & C Annex
410 Church Street
Nashville, TN 37243-1534

In Tennessee, substances or conditions that do not currently have numeric national criteria have impacted a considerable number of streams. Narrative criteria, which are based on a verbal description of water quality, have been historically used to regulate potential pollutants such as nutrients, habitat alteration, siltation, and loss of biological integrity. Accurate water quality assessment on the state level requires the ability to appropriately interpret these narrative water quality criteria.

Additionally, for some conditions such as dissolved oxygen levels and pH, Tennessee has historically incorporated statewide numeric water quality goals based on the national criteria. However, this one-size-fits-all approach clearly has its limitations in a state that contains high gradient, pristine mountain streams in the east and low gradient delta streams in the west.

In order to develop water quality criteria that better reflect Tennessee's naturally diverse aquatic systems and to improve our ability to perform water quality assessments, between 1992 and 2002, the Tennessee Division of Water Pollution Control undertook a comprehensive study of reference conditions. This project was accomplished in several stages: establishment of subecoregion boundaries; identification of reference streams; collection of biological, chemical, and physical data; analysis of data; and development of water quality criteria.

In 2003, the Division proposed a set of criteria revisions that incorporated the concept of reference conditions and recognized natural water quality variability. New regionalized numeric criteria were established for dissolved oxygen and pH. New narrative criteria, along with interpretation methodologies, were also created for nutrients, habitat, and biological integrity.

Keywords: water quality standards, water quality assessment, nutrient criteria, biological integrity, reference streams, jabberwocky.

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