Standard Test Method for
Analysis of Phytoplankton in Surface Water by the
Sedgwick-Rafter Method1

This standard is issued under the fixed designation D 4148; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.

1. Scope

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 SedgwickRafter 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 103 oculars the maximum overall magnification is
approximately 2503. 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.

2. Referenced Documents

2.1 ASTM Standards: 2
D 1129 Terminology Relating to Water
D 1193 Specification for Reagent Water
D 3370 Practices for Sampling Water
D 4149 Classification for Sampling Phytoplankton in Surface Waters

2.2 Various taxonomic keys are required for identification
of the algae. No single key is suitable for all species likely to
be encountered. (See Greeson 1977; Weber 1973.)

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