Overview

The Biological Assessment Branch is charged with evaluating the water quality of rivers and streams using the biological communities that live there. These biological communities can reflect both long and short term environmental conditions given the variety of life cycles these organisms exhibit (from less than one to several years in duration).

Biocriteria have been developed using the diversity, abundance, and pollution sensitivity of the organisms that inhabit lotic (flowing) waterbodies in NC. One of five bioclassifications are typically assigned to each water body sampled: Excellent, Good, Good-Fair, Fair and Poor. These bioclassifications, which have been developed for major ecoregions, are used to assess the various impacts of both point source discharges and nonpoint source runoff. The resulting information is used to document both spatial and temporal changes in water quality, and to complement water chemistry analyses, ambient toxicity data, and habitat evaluations. In addition to assessing the effects of water pollution, biological information is also used to define High Quality or Outstanding Resource Waters, support enforcement of stream standards, and measure improvements associated with management actions. The results of biological investigations have been an integral part in North Carolina's basinwide monitoring program.

Benthic Macroinvertebrates

Benthic macroinvertebrates are composed of aquatic insects but also include: crustaceans such as crayfish; molluscs like mussels, clams and snails; and aquatic worms. Many of these organisms are associated with the bottom substrates of rivers and streams or the submerged sides of stream channels. Many of the aquatic insects collected in freshwater habitats in North Carolina reside for long periods (from several months to three years) in their larval stage before emerging as an adult for a relatively short aerial or terrestrial existence. WSS biologists focus is on the aquatic stage of these organisms. Waters with Excellent or Good water quality will contain diverse, stable and pollution-sensitive communities of aquatic macroinvertebrates.

Fish Communities

Fish occupy the upper levels of aquatic food webs and are both directly and indirectly affected by chemical and physical changes that occur in rivers and streams. The Biological Assessment Branch employs an additional standard method for assessing the biological integrity of wadeable streams across the state by examining the structure and health of fish communities that inhabit them. Consistent with benthic macroinvertebrates, flowing waters with Excellent or Good water quality and habitats will contain robust, stable and pollution-sensitive fish communities.

Fish Tissue Contaminants

Since fish spend their entire lives in water, they are exposed to chemicals that occur in their aquatic environments and incorporate them into their body tissues primarily through dietary uptake. Contamination of aquatic resources, including freshwater, estuarine, and marine fish and shellfish species have been documented for heavy metals, pesticides, and other complex organic compounds in NC. Statewide fish tissue monitoring data is used by the NC Department of Health and Human Services for calculating potential risks associated with the consumption of local fish species and issuing fish consumption advisories when necessary.

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