Sampling, Biomass Estimation and Counts of Freshwater Algae - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 67

Volume counting chambers: the
Sedgwick-Rafter slide and Lund
nanoplankton counting chamber

sample is fully mixed by gentle inversion and agi-
tation.

2. Remove a sample of fully mixed algal suspen-
sion using a wide-aperture pipette. With the cov-
erslip placed across the Sedgwick-Rafter slide
(Fig. 2.13b), fill the chamber with sample. Rotate
the coverslip back to completely cover the cham-
ber, taking care to excluding air bubbles.

Sedgwick-Rafter slide This contains a shallow
central chamber that has a capacity of 1 ml, an
engraved grid of 1000 squares (Fig. 2.13a) and is cov-
ered by a thick coverslip. The volume of the chamber
should be checked either by taking accurate measure-
ments of its dimensions or by accurately weighing the
slide (including cover slip) dry and then reweighing
it filled with distilled water.
Species counts can be made as follows:

3. Allow the algal cells to settle to the bottom of the
chamber and examine with the 20× objective of
an inverted-objective or conventional microscope.

4. Before making any counts, scan the whole cham-
ber to identify major species present in the sam-
ple plus any other species of interest. If any

1. After removal from the storage container (e.g.
refrigerator), allow the iodine sample to equili-
brate to room temperature, and make sure that the

(a) Sedgwick-Rafter counting
slide

(b) Filling the chamber with
algal suspension.

Pipette

(c) Counting within single square

A B

Included-

Not included-

C

D

(d) Counting over successive squares

1 2

Figure 2.13 The Sedgwick-Rafter
slide:designofcountingchamberand
protocol for making counts.

3