Techniques for the Quantification Density of Microplankton Populations
273
this group attains 2-3 orders, and their density in the natural populations
3-4 orders of values. Therefore, the selection of proper methods for phytoplankton quantification first of all depends upon the kind of population met
by the researcher. The use of a universal method everywhere (as is still
common practice) can be a source of grave errors, measured not by percentagt:: but as many dt::grees of underestimation, and may result in missing important taxonomic groups. Therefore, first of all, the researcher should be able
to control the approximate density and composition of phytoplankton before
deriving the sampling program and the technique of sample processing. For
this, I recommend viable microscope examination of a nonconcentrated water
sample in a simple glass chamber 1-1.2 mm deep. The chamber for this purpose
could be made of a plastic frame with this thickness (see Fig. 6.3) glued to the
surface of a microscope slide. The chamber is filled with intact freshly taken
natural water. Being covered with a large cover slide, its content is observed
at a magnification of 200-300 in the darkened or phase contrast field. These
observations give a presentation of the rough biomass and taxonomic composition. This provides the possibility to select a combination of methods to
be optimally applied; in my opinion, an adequate evaluation of both the above
parameters can only be achieved in most cases using the combination of complementary techniques.
1. The Utremohl sedimentation method
This is the most common method for the concentration and subsequent
quantification of phytoplankton and for estimation of its size and taxonomic
composition. As fixers, the users of this method apply Utremohl or Lugol
iodine solutions or formalin at 0.5% of its final concentration. The method is
accepted by a majority of hydro biologists as a universal one. It was used, as a
rule, disregarding the density or composition of native phytoplankton populations, which is quite wrong. The sedimentation technique may give reliable
information about the density of some groups of microalgae, when applied
under the following conditions: (1) samples, collected in the field, must be distributed into the sedimentation vessels within 2-3 h, being fixed only there, and
not before. In a sample preserved for over a week with any of the above listed
fixatives, the researcher can observe some remains of large algae, but not their
real popUlation; (2) the method can be used only in combination with some
other technique, which is needed to account for those phytoplankton groups
which in any case are missing with the sedimentation technique, such as the
picoalgae, the small «3-5-llm) nanoflagellates, and the larger cyanobacteria,
which most often float rather than settle in the sedimentation vessels; (3) the
sedimentation method may be used for the quantification of only diatoms,
dinoflagellates, and other micro- and nanoalgae >10 11m size (except cyanobacteria). As a complementary technique for the sedimentation method, the
epifluorescence method can be used to account for the losses of the above
listed groups of algae, which often dominate the phytoplankton population not
only by their numerical abundance, but also by their biomass.
273
this group attains 2-3 orders, and their density in the natural populations
3-4 orders of values. Therefore, the selection of proper methods for phytoplankton quantification first of all depends upon the kind of population met
by the researcher. The use of a universal method everywhere (as is still
common practice) can be a source of grave errors, measured not by percentagt:: but as many dt::grees of underestimation, and may result in missing important taxonomic groups. Therefore, first of all, the researcher should be able
to control the approximate density and composition of phytoplankton before
deriving the sampling program and the technique of sample processing. For
this, I recommend viable microscope examination of a nonconcentrated water
sample in a simple glass chamber 1-1.2 mm deep. The chamber for this purpose
could be made of a plastic frame with this thickness (see Fig. 6.3) glued to the
surface of a microscope slide. The chamber is filled with intact freshly taken
natural water. Being covered with a large cover slide, its content is observed
at a magnification of 200-300 in the darkened or phase contrast field. These
observations give a presentation of the rough biomass and taxonomic composition. This provides the possibility to select a combination of methods to
be optimally applied; in my opinion, an adequate evaluation of both the above
parameters can only be achieved in most cases using the combination of complementary techniques.
1. The Utremohl sedimentation method
This is the most common method for the concentration and subsequent
quantification of phytoplankton and for estimation of its size and taxonomic
composition. As fixers, the users of this method apply Utremohl or Lugol
iodine solutions or formalin at 0.5% of its final concentration. The method is
accepted by a majority of hydro biologists as a universal one. It was used, as a
rule, disregarding the density or composition of native phytoplankton populations, which is quite wrong. The sedimentation technique may give reliable
information about the density of some groups of microalgae, when applied
under the following conditions: (1) samples, collected in the field, must be distributed into the sedimentation vessels within 2-3 h, being fixed only there, and
not before. In a sample preserved for over a week with any of the above listed
fixatives, the researcher can observe some remains of large algae, but not their
real popUlation; (2) the method can be used only in combination with some
other technique, which is needed to account for those phytoplankton groups
which in any case are missing with the sedimentation technique, such as the
picoalgae, the small «3-5-llm) nanoflagellates, and the larger cyanobacteria,
which most often float rather than settle in the sedimentation vessels; (3) the
sedimentation method may be used for the quantification of only diatoms,
dinoflagellates, and other micro- and nanoalgae >10 11m size (except cyanobacteria). As a complementary technique for the sedimentation method, the
epifluorescence method can be used to account for the losses of the above
listed groups of algae, which often dominate the phytoplankton population not
only by their numerical abundance, but also by their biomass.