Bioassessment and Biocriteria Program Status for North Carolina: Streams and Wadeable Rivers
State Program Contact
Water Quality Standards
The link to North Carolina's WQS that are in effect for Clean Water Act purposes is provided. These are the WQS approved by EPA.
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Designated Aquatic Life Uses
ALU is based on a 5-tiered system of bioclassifications for perennially flowing waters: Excellent, Good, Good-Fair, Fair, and Poor. A water body receiving a bioclassification of Fair or Poor does not meet its designated Aquatic Life Use and is placed on the 303d list. All other bioclassifications result in a “Supporting” ALU. Additionally, in NC we also use Excellent bioclassifications in support of the supplementary (and more protective) Surface Water Classifications of Outstanding Resource Waters (ORW) and High Quality Waters (HQW). More information on that process can be found in the North Carolina DENR - Division of Water Quality "Redbook" (PDF) (15A NCAC 02B .0224 and 15A NCAC 02B .0225) (99 pp, 2 MB)
Classifications located at 15A NCAC 02B .0301 (PDF)(99 pp, 2 MB)
__X__ Narrative, with quantitative implementation procedures or translators
_____ No criteria
Narrative Biocriteria located at 15A NCAC 02B .0211 Fresh Surface Water Quality Standards for Class C Waters (PDF) (99 pp, 2 MB)
Class C: freshwaters protected for secondary recreation, fishing, aquatic life including propagation and survival, and wildlife. All freshwaters shall be classified to protect these uses at a minimum.
Class SC: saltwaters protected for secondary recreation, fishing, aquatic life including propagation and survival, and wildlife. All saltwaters shall be classified to protect these uses at a minimum.
Outstanding Resource Waters (ORW): unique and special waters of exceptional state or national recreational or ecological significance which require special protection to maintain existing uses. (5) High Quality Waters (HQW): waters which are rated as excellent based on biological and physical/chemical characteristics through Division monitoring or special studies, native and special native trout waters (and their tributaries) designated by the Wildlife Resources Commission, primary nursery areas (PNA) designated by the Marine Fisheries Commission and other functional nursery areas designated by the Marine Fisheries Commission, all water supply watersheds which are either classified as WS-I or WS-II or those for which a formal petition for reclassification as WS-I or WS-II has been received from the appropriate local government and accepted by the Division of Water Quality and all Class SA waters.
Antidegradation Policy located at 15A NCAC 02B .0201 (PDF) (99 pp, 2 MB)
What biological assemblages are used in the bioassessment program?
Benthic macroinvertebrates and fish
Are bioassessments used to support 303(d) listings?
Yes. Listing methodology: 2020 303(d) Listing and Delisting Methodology (PDF)(14 pp, 404 K) (Page 7)
How are assemblages used to make impairment decisions?
The same assessment categories are used for both Fish and Benthos (ranging from Excellent to Poor for permanently flowing waters, and Natural to Severe for seasonally flowing swamp waters), but they are used independently. In other words, if at the same location benthos rate Good and fish rate Good-Fair, both are given equal weights. There is no averaging or differential weightings.
Other uses of biocriteria or bioassessment within the water quality program:
Antidegradation, 305(b) surface water condition assessments, TMDL development and assessment, non-point source assessments, BMP evaluation, and restoration goals
Technical Support Information and Documents:
The process used to choose reference sites begins with evaluation of existing benthos and fish community sample sites. For those sites in potentially least-impacted areas, land use in the watershed is determined using: %Forest/Water/Wetland; %Agriculture/Cropland; %Grass/Shrub; %Suburban; %Urban/Barren. Attempts are made to obtain reference sites from a range of watershed areas in each ecoregion. Sites with any of the following characteristics are NOT considered for reference conditions: low “natural” landscape area, the presence of NPDES dischargers upstream (small or medium watersheds), or the presence of a potential local source of impact.
Development of biocriteria involves the collection and interpretation of biological data –e.g. benthic macroinvertebrates and fish communities. During this process entities typically use biological metrics (usually aggregated into a multimetric index) and/or multivariate analysis to assess whether a waterbody is meeting its designated aquatic life use(s). The reference materials included below include standard operation procedures used in data collection, compilation, technical approaches used to develop biocriteria as well as its implementation procedures.
Technical reference material:
Benthos: Standard Operating Procedures for Collection and Analysis of Benthic Macroinvertebrates (PDF)(78 pp, 3 MB)
Fish: Standard Operating Procedure Biological Monitoring-Stream Fish Community Assessment Program (PDF)(52 pp, 4 MB)
Stressor identification/causal analysis approach:
For a given biological sample, North Carolina’s bioassessment analysis and approach process involves the evaluation of the 1) water quality bioclassification for that sample, 2) an evaluation of the individual metrics used to derive that bioclassification, 3) a detailed, taxa-by-taxa analysis of the sample’s community structure, 4) evaluation of the abundance of the taxa present in the community, 5) an evaluation of the effect of season on community structure, 6) current and historic landuse patterns in the watershed, 7) current and historic water chemistry patterns, 8) current and historic hydrological alterations (or lack thereof), 9) the influence of ecoregion on community structure, and 10) the effect of habitat. For each biological sample, these factors are examined holistically to provide a definitive interpretation of the bioassessment as it relates to water quality.