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the first sign of an adverse reaction (for example, hives or difficulty in breathing). Field personnel who are sensitive or allergic to bee or wasp stings should inform their project chief and avoid situations where they might be stung.

Field teams should always be composed of at least two people; no one should sample alone. All individuals in the field sampling team should be trained in basic first aid and cardiopulmonary resuscitation techniques. Each field team should be equipped wi th a suitable first-aid kit and, when possible, a cellular telephone for emergencies. A list of medical facilities closest to each sampling site should be developed and carried in each field vehicle.


Benthic invertebrate communities are characterized in the U.S. Geological Survey's National Water-Quality Assessment Program as part of an integrated physical, chemical, and biological assessment of the Nation's water quality. This multidisciplinary approach provides multiple lines of evidence for evaluating water-quality status and trends, and for refining understanding of the factors that control water quality. This is accomplished by integrated, multiyear sampling at sites chosen to represent combina tions of natural and anthropogenic factors that are important in influencing water quality locally, regionally, and nationally.

Benthic invertebrate communities are an important part of biological water-quality assessment because these organisms live in, on, or near streambed sediments where hydrophobic chemicals tend to concentrate. These organisms integrate exposures over a period of approximately a year (depending upon the length of the life cycle) and, because they are relatively sessile, characterize effects over a relatively small spatial area. They also respond to a wide variety of natural and human-engendered influences, including sedimentation, hydrologic changes, thermal pollution, xenobiotics, habitat modification, and eutrophication. These characteristics make them well suited for use in (1) assessing site-specific water-quality conditions, (2) comparing spatial pat terns of water quality,
(3) integrating effects over an annual cycle, and (4) relating biological effects to physical and chemical measures of water quality.

The basis for invertebrate community characterization is the sampling reach, which is usually a length of river containing multiple examples of the dominant geomorphic features that characterize the stream segment. Each sampling reach is characterized us ing a combination of qualitative and semi-quantitative methods. A three-level hierarchy of geomorphic and channel characteristics is used to define a matrix of 51 instream habitat types. The habitat matrix supplies information used to determine where qu alitative and semi-quantitative samples are collected in the sampling reach and what types of samplers and collection methods are used.

Qualitative benthic invertebrate samples are collected from as many of the instream habitat types as are present and accessible within the sampling reach. These qualitative