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1.1 This test method covers determining the density and taxonomic classification of phytoplankton. It is applicable both to relatively sparse or dense phytoplankton concentrations, provided the suspended-sediment concentration is low. The Sedgwick Rafter (S-R) method requires less costly apparatus than does the inverted microscope method but gives less accurate results. The inherent inaccuracy in the Sedgwick-Rafter method is due to the design of the counting chamber and cannot be circumvented by a different choice of optics. For this reason, the S-R method is limited to the use of objective lenses having a working distance of approximately 1.6 mm or more. With 10× oculars the maximum overall magnification is approximately 250×. High concentrations of suspended sediment can obscure the algal cells, and thus cause interference.

1.2 This test method is applicable to both freshwater and marine samples.

1.3 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific precautionary information see Section 8.

4.1 Phytoplankton are basic to the food chain in all aquatic environments. In addition, they have long been considered to be important indicators of water-quality conditions. Phytoplankton data are also frequently used in the planning and design of water-treatment facilities and reservoirs.