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The combination of physical, chemical, and biological data to be collected as part of NAWQA provides an integrated assessment of water quality within selected environmental settings. Natural and human factors that influence the quality of water will be addressed in the integrated-assessment approach of the NAWQA Program. These factors include ecoregion, geology, hydrology, and stream size, as well as land- and water-use activities. The objectives of NAWQA ecological surveys are to characterize benthic invertebrate (Cuffney and others, 1993), fish (Meador, Cuffney, and Gurtz, 1993), and algal communities, in addition to documenting instream and riparian habitat conditions (Meador, Hupp, and others, 1993).

The algal component of NAWQA ecological surveys is designed primarily to characterize the species distribution and community structure of benthic algae (periphyton) and their relation to water quality. Estimates of algal biomass (for example, ash-free dry mass and chlorophyll content) are optional and may be made in some study units. The collection of phytoplankton samples (or the use of artificial substrates for collecting periphyton samples) may be considered for large, nonwadeable streams and rivers. Stream locations are chosen to represent major natural and human factors that are thought to significantly influence the quality of water. The sampling reach, described by Meador, Hupp, and others (1993), represents the sampling unit for ecological ass essments within NAWQA study units. Relations among biological community structure, water chemistry, and major natural and human factors among NAWQA study units form the basis for a national synthesis of water-quality conditions and trends.

Periphyton samples for NAWQA ecological surveys typically are collected in conjunction with the sampling of benthic invertebrates described by Cuffney and others (1993). Periphyton microhabitats are submerged surfaces in streams and rivers, such as rocks, logs, plants, sand, and silt, that support the attachment and growth of algae. Qualitative periphyton samples are intended to provide a list of species (taxa richness) present in the sampling reach. Samples of algae are collected from each periphyton microhabitat present in the sampling reach and composited into one sample. Quantitative periphyton samples are collected to measure the relative abundance and density (algal cells per square centimeter) of each taxon present in each of two contrasting in stream habitat types in a sampling reach. Quantitative samples are collected using a variety of sampling devices; the appropriate choice of sampling equipment is dictated by the character of the dominant periphyton growth forms and microhabitats in the s ampling reach.

Three sampling reaches are established at a subset of the NAWQA basic fixed sites to assess spatial and short-term temporal variability. For each of these intensive ecological assessments, one reach will be sampled every year for 3 successive years to as sess short-term temporal changes. To evaluate the magnitude of reach-to-reach variability, two additional reaches will be sampled during 1 of the 3 years. Periphyton data will be related to corresponding physical, chemical, and biological data at each basic fixed site to evaluate taxon-specific responses to differences or changes in water and sediment chemistry, to assess the effects of algal communities on water quality, and to integrate physical, chemical, and biological characteristics into regional and national assessments of water quality.

Purpose and Scope

This report describes methods, procedures, and equipment for collecting algal samples at basic fixed sites as part of the U.S. Geological Survey's NAWQA Program. The sampling