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The "Sampling Information" section of the field data sheet contains entries for the total number of containers included in the sample, the type and volume of algal preservative used, and qualitative observations of periphyton abundance and recog nizable algal taxa. Periphyton microhabitats present in the sampling reach are circled; if desired, the relative percentage of each microhabitat is estimated and recorded. Periphyton growth-forms present in the reach (macroalgae, microalgae, and aquat ic mosses) are indicated by circling the sample types collected and recording the sample identification number for each one.

Quantitative Targeted-Habitat Periphyton Samples

Quantitative periphyton samples provide data on the occurrence and abundance of benthic algal taxa in two contrasting instream response habitats: (1) a richest-targeted habitat (RTH), which supports the taxonomically richest assemblage of organisms within a sampling reach, and (2) a depositional-targeted habitat (DTH), where organisms are likely to be exposed to sediment-borne contaminants for extended periods of time. Examples of RTH habitats include a riffle in a shallow, coarse-grained, high-gradient stream (epilithic periphyton microhabitat) or snag habitats in a sandy-bottom, Coastal Plain stream (epidendric periphyton microhabitat). The DTH habitat is typically an organically rich, depositional area such as a pool (epipelic or epipsammic microhabi tats). The selection of an appropriate RTH is based on information derived during the NAWQA retrospective data analysis, input from the study-unit liaison committee, consultation with the USGS regional biologist, and results from reconnaissance sampling.

The objective of quantitative habitat-based sampling of periphyton is to obtain representative algal samples from the predominant periphyton microhabitat in each of two instream habitats (RTH and DTH). These objectives parallel those described for benthic invertebrates (Cuffney and others, 1993). When periphyton sampling is conducted in association with benthic invertebrate sampling (for example, at NAWQA basic fixed sites), representative microhabitats are sampled from the same general location in the sampling reach as the benthic invertebrate samples. The quantitative periphyton samples should be obtained prior to collecting qualitative algae and benthic invertebrate samples unless there are sufficient personnel and space within the sampling reach to ensure that the two sampling activities do not interfere with one another. Sampling should begin at the downstream end of the sampling reach and progress upstream.

Richest-Targeted Habitats

The purpose of collecting quantitative samples of microalgae is to measure algal abundance, species composition, and community structure in the predominant periphyton microhabitat of the RTH selected for sampling benthic invertebrates. Periphyton microhabitats in the RTH generally can be classified as epilithic, epidendric, or epiphytic; however, the RTH in some sampling reaches may be characterized by epipsammic or epipelic microhabitats. In addition to relative abundance information, which is required for NAWQA ecological surveys at basic fixed sites, optional information may include density and biovolume of algal species, chlorophyll a and b, ash-free dry mass, and other properties of the periphyton community. The appropriate pe riphyton sampling methods, as well as the components to be measured, should be chosen in consultation with the regional biologist and dictated by microhabitat conditions of the instream habitats selected in the sampling reach.