Collections of biological communities and characterizations of riparian and instream habitat conditions are made for at least one sampling reach at each Basic and Intensive Fixed Site. For wadeable streams, the acceptable range for sampling reach length usually ranges from 150 to 500 m, but longer reaches may be necessary in nonwadeable streams. Criteria for minimum and maximum reach lengths are used to provide a sampling-reach length sufficient to ensure the collection of representative samples from, for example, the fish community. Fish are identified as to species, length and weight are recorded, and the presence of external anomalies, which include skeletal deformities, eroded fins, lesions, tumors, diseases, and parasites, is noted. In addition, a qualitative sample from all instream habitat types in the reach provides a more complete list of taxonomic groups present at the time of collection.
All samples are composites collected throughout the entire reach.
All algal samples are collected in a semiquantitative manner. Basin descriptors are recorded as part of the Environmental Framework of each site and include such variables as ecoregion, physiographic province, geology, soils, climate, and land use. Habitat characterizations at the reach scale include geomorphic channel units, such as riffle, run, and pool, as well as physical features of the channel, bank, and flood plain and observations of dominant species of woody vegetation and macrophytes. Habitat characteristics that are associated with individual biological samples include substrate particle size, water depth, and velocity. Sampling of biological communities is conducted during similar hydrologic and seasonal conditions for all fixed sites in the Study Unit.