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The Importance of Biocriteria in North Carolina's Basinwide Management Strategy

Program Overview

The North Carolina Division of Water Quality (DWQ) has been using bioassessment techniques to evaluate water quality for more than 15 years. The basin-wide management program includes all 17 of the state's major river basins, which are assessed on a 5-year cycle. Macroinvertebrate samples are used to calculate EPT (Ephemeroptera-Plecoptera-Trichoptera) taxa richness and a biotic index; the waterbody is then classified on a scale from Poor to Excellent. Fish community assessments use an Index of Biotic Integrity (NCIBI), which is based on twelve fish metrics and classifies the waterbody using the same scale as that used for the benthos. North Carolina's narrative biocriteria, established to protect aquatic life and assess water quality impairment, have proven especially valuable in supporting decisions to implement management strategies to address impairment. Bioassessments provide water quality status and trend information for 305(b) reporting; are the preferred source of information in assessing use support, and are used extensively in 303(d) listings. They are used in permitting, enforcement, and litigation support; in habitat modification situations (404 permits); in evaluating waste sites such as landfills; and in setting priorities for wetlands restoration.

Biocriteria as a Tool in Watershed Management

Water quality planning and management are conducted in North Carolina on a river basin by river basin basis. Activities such as permitting, monitoring, modeling, non-point source assessments, and planning are coordinated and integrated by basin. This coordination results in improved efficiency and effectiveness, achieves better consistency and equitability, and increases public awareness of the state's water quality programs. The components of a basinwide water quality assessment include monitoring of benthic macroinvertebrates and fish populations, fish tissue analyses, lake assessment (including phytoplankton monitoring), special chemical/physical water quality investigations, and monitoring of aquatic toxicity, sediment oxygen demand, and ambient water quality.

north carolina basinsUnique factors of the particular river basins must be considered in the proper application of biocriteria. This need was particularly evident during the second planning cycle for the Lumber River Basin. The 1994 Lumber River Basinwide Water Quality Management Plan was only the second basin plan to be developed, and the concept and methodology for basinwide planning was still new. During the intervening five-year period, many improvements in the methodology and technology for assessing water quality impairment have been made, and the 1999 Lumber River Basinwide Water Quality Plan reflects these changes. The Lumber River Basin is unique in that 90% of its waters are swamp waters, having naturally low productivity and pH and dissolved oxygen stresses that are not found in more typical flowing water systems. Recent work on swamp streams suggests that different biocriteria should be used for slow flowing, swamp-like systems. Four years of study indicated that benthos data collected during the normal summer sampling period were unable to distinguish differences in impact; thus, only the data collected during the winter high flow periods are used for water quality classification. A procedure that could be used in deep (non-wadeable) coastal streams to sample fish communities using boats is also under development.

The DWQ has developed draft swamp stream rating criteria based on a habitat score and on benthic macroinvertebrate community data collected in winter. Reference site data collected with these new techniques further evaluated and refined the criterin and illustrated that the swamps in the northern and southern parts of the state must be evaluated differently. Swamp data are not valid for use support.

Biological data is also a valuable tool for classifying Outstanding Resource Waters (ORW) and High Quality Waters (HQW). In order to be classified as ORW or HQW, the stream must receive a biological rating of "Excellent." For example, the French Broad River Basin in the western mountains of the state has generally high water quality. Much of the basin is within the Pisgah National Forest or Pisgah Game Lands, and assessments conducted during the period from 1983 to 1992 at 152 sites demonstrated that more than half of the sampling sites were rated as Excellent or Good. The most recent water quality management plan for the basin identified 12 stream segments that would qualify for upgraded classification, based on biosurvey data that resulted in Excellent ratings. State standards allow waters designated as ORW or HQW to be protected through such means as advanced treatment requirements, restriction of new discharges, land use regulations, and storm water controls.

Lesson Learned

Biocriteria are a useful tool for managing water quality on a watershed basis, as the resident biota are reflective of the unique characteristics of the watershed. Protection of special classes of high quality waters in North Carolina would not be possible without bioassessment data.

Additional Information

Trish MacPherson ( at NCDWQ at 919-733-6946.


North Carolina Department of Environment, Health, and Natural Resources, Division of Environmental Management, Water Quality Section, 1995. French Broad River Basinwide Water Quality Management Plan.

North Carolina Department of Environment, Health, and Natural Resources, Division of Environmental Management, Water Quality Section, 1994. Basinwide Assessment Report Support Document: French Broad River Basin.

North Carolina Department of Environment, and Natural Resources, Division of Water Quality, Water Quality Section, 1999. Lumber River Basinwide Water Quality Plan.

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