Three taxonomic groups--fish, invertebrates, and algae--are sampled because they respond differently to various environmental stresses. Fish are valuable biological indicators of long-term water-resource conditions because they are long lived (years to decades) and have considerable economic value and public interest. Benthic invertebrates (aquatic insects, mollusks, crustaceans, worms) have life cycles (from months to a few years) that are intermediate between fish and algae, have close association with streambed sediments, and can be used for characterizing changes in water quality over small spatial areas. Algae respond quickly (within days to weeks) to changes in their environment and serve as valuable biological indicators of rapid changes in water-resource conditions.
Representative samples of the fish community are collected from the stream reach by using a combination of sampling methods to determine species presence and abundance (Meador, Cuffney, and Gurtz, 1993); the two primary sampling methods used are electrofishing and seining. 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.
Three types of benthic invertebrate samples are collected in each sampling reach (Cuffney and others, 1993b). Semiquantitative samples provide information on the abundance of taxa present in two targeted habitats--one that is expected to support the highest number of taxa within the reach (for example, riffles or woody snags) and a depositional habitat (for example, pool). 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.
The algal community is sampled from each of the habitats targeted for benthic invertebrates and a multihabitat composite sample is also prepared (Porter and others, 1993). All algal samples are collected in a semiquantitative manner.
Habitat characterizations of channel, bank, and flood-plain features follow a spatial hierarchy that incorporates basin, stream segment, stream reach, and sample descriptors (Meador, Hupp, and others, 1993). 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. Stream-segment data are obtained from geographic information system databases and topographic maps and include information on stream meandering, gradient, elevation, and water-management features. 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.
Fixed-Site Reach Assessments are done at least once at each Basic and Intensive Fixed Site during the 3 years of the intensive data-collection phase. Sampling of biological communities is conducted during similar hydrologic and seasonal conditions for all fixed sites in the Study Unit. Scheduling of sample collection takes into consideration several factors, which include hydrology, life histories of aquatic species, accessibility of sites, and timing of major human activities.
Sites for Intensive Ecological Assessments (typically three to four sites) are chosen to represent a range of water-quality conditions, stream sizes, and habitat conditions within each Study Unit. Reach-to-reach variability is estimated at these sites by sampling multiple (minimum of three) reaches that are located so that each represents similar water-quality conditions to the fixed site. Year-to-year variability is described by sampling one of the three reaches during each year of the 3-year intensive data-collection phase. Sampling and sample-processing strategies for each reach are identical to those for the Fixed-Site Reach Assessments.
Ecological Synoptic Studies usually focus on the relation of selected Environmental Setting characteristics to selected biological community characteristics. For example, the distribution of fish species may be assessed for small and moderate-sized streams within urban, agricultural, and undeveloped settings. The design is coordinated wherever possible with that of Water-Column Synoptic Studies in the same Study Unit and among Study Units to address questions of regional or national interest. Priorities for Ecological Synoptic Studies are evaluated based on the potential to address relations among physical, chemical, and biological characteristics; the areal extent of a water-quality problem or biological issue; and the degree to which the design contributes to regional understanding and current National Synthesis topics. Results of the Retrospective Analysis, information on land-use patterns and local priority issues, and ecological information obtained from field reconnaissance of sites are used to determine the design.
Most Study Units complete one to two Ecological Synoptic Studies during the second and third years of the 3-year intensive data-collection phase. Although, the strategy for site selection, sampling, and analysis is issue specific and usually include a subset of the biological components sampled at the fixed sites, nationally consistent methods are used so results can be compared among Study Units.
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