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Quantitative periphyton samples are collected to measure algal community structure and, optionally, chlorophyll content and ash-free dry mass within two contrasting instream habitat types: a taxonomically "richest" habitat (richest-targeted hab itat or RTH) and a depositional-targeted habitat (DTH). These samples, along with the corresponding chemical and physical data, are used to (1) characterize the community within the sampling reach, (2) compare reaches among environmental settings, (3) compare changes in communities over time, and (4) couple physical and chemical water-quality characteristics with biological characteristics. Specific locations of the RTH and DTH habitats within a stream reach are consistent with those selected for invertebrate sampling (Cuffney and others, 1993).

Periphyton Microhabitats

Periphyton microhabitats are relatively small areas of submerged surfaces in streams and rivers that support the attachment of algae or are otherwise associated with the accumulation of algal biomass. Periphyton may be collected by scraping, brushing, siphoning, or by other methods appropriate to each microhabitat.

Epilithic - periphyton attached to rocks, bedrock, or other hard surfaces. Remove rocks from water and scrape (or hand pick) algal material into a sample container using a pocket knife or brush. Bedrock may be sampled using a PVC pipe sampler or the periphyton sampling device described in the section, "Quantitative Targeted-Habitat Periphyton Samples." It is desirable to collect epilithic samples that represent all combinations of microalgal texture and pigmentation present on rocks wit hin the sampling reach in erosional and depositional areas.

Epidendric - periphyton attached to submerged tree limbs and roots, or on other wood surfaces. Collection methods are similar to those described for epilithic microhabitat.

Epiphytic - periphyton attached to submerged aquatic plants or macroalgae. Scrape or brush algal biomass attached to roots, stems, and leaves of aquatic vascular plants into a sample container. Squeeze the liquid contents of filamentous algal mats and aquatic vascular plants into the same container.

Epipelic - periphyton associated with fine streambed sediments. Motile algal taxa, such as diatoms, euglenophytes, and blue-green algae, occur in the top 5-10 mm of the surface sediment. Filamentous algae also can be loosely associated with, but not necessarily attached to, the streambed in depositional areas of the sampling reach. Collect epipelic algae with a disposable pasteur pipette and bulb or with a larger suction device, such as a poultry baster. The epipelon also may be collected with a spoon or scoop in wadeable streams or from the upper surface of sediment samples collected with an Ekman or Ponar dredge in nonwadeable streams and rivers. Periphyton collections should be attempted only when there is visible pigmentation, such as brow nish-gold or dark green, associated with the streambed. An attempt should be made to exclude excessive amounts of inorganic silt from the periphyton sample.

Epipsammic - periphyton associated with coarse streambed sediments, such as sand. Collection methods are similar to those described for epipelic microhabitat. Only the top 510 mm layer of sand should be collected.