Sampling, Biomass Estimation and Counts of Freshwater Algae - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 45

Horizontal positions within water body

Vertical position within water body

PROTOCOL
FOR
COLLECTION

Frequency of sampling

Time within seasonal cycle

Net (horizontal or vertical haul)

Volume sampler

MODE OF
COLLECTION

Integrated sampling

Sediment trap

Filtration (biomass determination)

Centrifugation

CONCENTRATION
OF SAMPLE

Flow cytometry (size/pigmentation
analysis and sorting)

Fixation and sedimentation
(cell counts)

Size separation
- Coulter counter

TOTAL ALGAL
BIOMASS:
Turbidity
Fresh/dry weight
Chlorophyll- a
concentration

SPECIES
COUNTS

Microscopic
identification & counts
- counting chamber

Lake populations

DATA
ANALYSIS

Conversion to
biovolumes

Figure 2.2 Sampling and assess-
ment of lake phytoplankton popul-
ations.

Calculation of biotic
indices

trophic status (see Section 3.2.3), algal productivity
and the development of major algal blooms within
the water body.
Broad ecological monitoring normally involves
taking samples from at least three separate points
across the lake (Fig. 2.3a) on any particular date.
Collection at more than one site is necessary because
of uneven horizontal distribution (patchiness), which
can be a source of sampling error. Samples can either
be combined together to make a composite sam-
ple or be analysed separately - allowing statistical
evaluation of biomass and species composition
(means ± SD) across the water body.

Sampling is normally carried out within the epil-
imnion or to just below the thermocline, corre-
sponding approximately to the main depth of light
penetration - the photic zone. This can be defined
(Sigee, 2004) as the vertical distance between the
lake surface and the light compensation point (depth
at which photosynthesis balances respiration). The
photic zone can be roughly estimated as twice
the Secchi disk reading (see Section 2.3.1) and is
the major zone of phytoplankton population and pro-
ductivity within the water column.
Frequency of sampling varies from once or twice
yearly (general checks on lake status - summer