Standard Operating Procedure for Phytoplankton Analysis ...

Sampling and Analytical Procedures
for GLNPO’s WQS
6.6.3.3 Gently homogenize the pellet and pipette about 0.5 mL of the concentrated sample on the center
of a coverslip and let dry. A larger or smaller aliquot may be used depending on the diatom
densities. Observe under a compound microscope to be sure that there is an adequate density of
frustules to allow counting. If there is not a sufficient density for counting, increase frustule
density by adding more sample.
6.6.3.4 Add a drop of Hyrax mounting medium to the center of a clean pre-labeled slide (75 x 25 mm).
If the Hyrax mounting medium is too viscous, add a few drops (1 to 2 mL) of toluene and/or
xylene to dilute the medium.
6.6.3.5 Mount the coverslip, diatom side down, on the slide and place on hotplate.
6.6.3.6 Allow solvent to evaporate until bubbles are no longer formed under the coverslip. Remove from
hotplate.
6.6.3.7 Press coverslip gently with pencil eraser or tweezers to extrude excess Hyrax immediately after
removing from heat, as the medium sets up very quickly.
6.6.3.8 Allow slide to cool and remove excess Hyrax before examining. It will scrape away easily with a
razor blade if all of the solvent is removed: if it is sticky, return to the hotplate to remove any
remaining solvent.
6.6.3.9 Clean, label, and store the slide properly. The label should include the sample number, year, and
station.
6.6.4 Diatom Enumeration and Identification
6.6.4.1 Diatoms should be identified and enumerated at 1250x. Identification should be down to the
lowest taxonomic rank possible.
6.6.4.2 Count at least 500 frustules (2 frustules = 1 diatom cell) per sample.
6.6.4.3 At least 10 specimens of each species are measured (wall to wall) for cell volume calculations.
When fewer than 10 specimens are present, those present are measured as they occur.
Measurements should be recorded as cell measurements, not frustule measurements. For
example, when measuring the depth (i.e., length) of Aulacoseira, be sure to either measure two
frustules together, or double the measurement of a single frustule. In some species, e.g. most
Stephanodiscus and Cyclotella, depth measurements are problematic in that cells are seldom
oriented in girdle view, and even when they are, total cell depth is not easily estimable from the
depth of a single frustule due to overlap of the girdles. Care must therefore be taken in making
these measurements.
6.6.5 General Analysis Guidelines
6.6.5.1 Unknown species should be referred to as Genus spp. Taxa for which in-house descriptions exist,
but descriptions have not been published, should be given the appropriate number (e.g.,
Stephanodiscus #10). It is crucial that these designations correspond only to previously
established taxa. Numbered taxa appearing on the species list, but for which no descriptions have
been found, are never to be used. If an analyst encounters a species that is not on the species list,
it must be confirmed by an outside expert and approved by the Work Assignment Manager
(WAM) before it is added to the species list. In the case of >soft= algae, the organism should be
Page 6 LG401, Revision 05, February 2010