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USGS Data Series 423
National Water-Quality Assessment Program
Biological data were collected from the stream reaches established for characterizing instream habitat. Standard NAWQA sampling protocols were used to collect algae (Porter and others, 1993, for BOS, BIR, and SLC; Moulton and others, 2002, for RAL, ATL, MGB, DEN, DFW, POR); benthic macroinvertebrates (Cuffney and others, 1993, for BOS, BIR, and SLC; Moulton and others, 2002, for RAL, ATL, MGB, DEN, DFW, POR); and fish communities (Moulton and others, 2002). Quantitative samples for the algal and invertebrate communities were composed of five subsamples from riffles with cobble and gravel substrates or woody snags. This sample was called the richest targeted habitat (RTH) sample because, in these streams, riffles were presumed to contain the richest assemblage of algae and macroinvertebrates. In the Atlanta and Dallas-Fort Worth studies, RTH samples were collected from woody debris and snags by cutting pieces of branches and scraping the surfaces into a collection container. The total area of snag samples was determined by considering each branch as a simple cylinder, calculating the area of each cylinder, and summing the areas.
Richest targeted habitat algal subsamples were collected by scraping the upper surface of cobbles collected from five riffle areas (three to five cobbles from each area) in conjunction with the collection of macroinvertebrate RTH samples. Foil templates were made of the surface areas of rocks from which the algal samples were collected, and these templates later were digitized to determine the areas sampled. For algae, an additional quantitative sample was collected from a composite of five samples from depositional targeted habitats (DTH) in areas of the stream that had little or no streamflow. These areas provide a unique habitat for algal communities that can include motile or sensitive species not found in the main streamflow areas. Depositional targeted habitat samples were collected by inverting a 47-millimeter (mm)-diameter plastic petri dish, gently pressing it into the sediment surface, sliding a spatula under the petri dish to trap the sediment, and removing the petri dish full of sediment.
Richest targeted habitat macroinvertebrate subsamples consisted of Slack samples (each were 0.25 square meters [m2]; a 500-micron mesh net was used in RAL, ATL, MGB, DEN, DFW, and POR; a 425-micron mesh was used in BOS, BIR, and SLC) from five separate riffle areas in the sampling reach and combined to form a single composite sample of 1.25-m2 area. In addition, a qualitative multi-habitat (QMH) sample was collected, which consisted of macroinvertebrates collected from as many habitats in the stream reach as were accessible. The QMH sample was collected by using a dip net (500-micron mesh in RAL, ATL, MGB, DEN, DFW, and POR; 210-micron mesh in BOS, BIR, and SLC) supplemented with hand picking of substrates. Sampling effort (measured as time) was apportioned as equally as possible among accessible habitats in the sampling reach.
Fish communities at each site were sampled at low-flow conditions by using published protocols (Meador and others, 1993, for BOS, BIR, and SLC; Moulton and others, 2002, for RAL, ATL, MGB, DEN, DFW, POR). Two electrofishing passes were completed in each stream reach, except in SLC, where a single pass was used. Fish were identified to species and counted. Species identifications were made or verified by regional taxonomic specialists. Voucher specimens and specimens that could not be definitely identified in the field were preserved in 10-percent formalin and kept for processing and identification.