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Counting units are individual cells,
filaments or colonies depending on the organization of the algae. A
minimum of 400 - 500 units (usually at multiple magnifications) from
randomly selected transects are counted for each sample; counting at
multiple magnifications allows us to correctly enumerate taxa present
that may vary by several orders of magnitude in size. In cases where a
sample has extremely few algal units and high particulate matter (thus
yielding less than 400 units), as many transects as possible will be
covered in order to have more than 70% of the chamber counted; the
entire chamber is counted when possible.
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Identification of diatoms to species
level involves boiling/digesting sub-samples in hydrogen peroxide in
order to clean the frustules, followed by mounting on glass slides
using Naphrax and identification at 1000X magnification under oil
immersion. The diatoms identified on the mounted slides are matched
with what are obtained in the fresh samples; where it is not possible
to separate two or more species in the fresh samples, separation is
done by proportion.