Sampling, Biomass Estimation and Counts of Freshwater Algae - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 44

Planktonic algae

A

B C D

Benthic
algae

m SEDIMENT

Figure 2.1 General occurrence of algae in the freshwater environment (not to scale). Freely suspended planktonic
algae present in surface waters (shaded area) are in equilibrium (dynamic interchange) with a range of sediment- or
macrophyte-associated organisms. (A) Epiphytic algae present on macrophytes (m) include filamentous and unicellular
forms. Filamentous algae may detach (

→

) to form planktonic filament masses (metaphyton). (B) Unattached algae on the
substratum include actively photosynthetic organisms (shallow waters) and dormant overwintering cells and colonies.
(C) Algae present within a biofilm. Along with other microorganisms, the algae may be enclosed within a mucilaginous
matrix ( □ ). (d) Extended growths of filamentous algae (with associated microalgae) form a dense mat (periphyton). The
filamentous algae are typically attached to solid surfaces such as rocks and stones ( ■ ).

and substrate mobility. In both cases, human activi-
ties - inflow discharges, recreational activities, water
removal and surrounding agriculture - may also be
important. As a final step, the past aquatic history of
the water body may also be of relevance - including
previous contemporary studies and analysis of the
sediments (see Section 3.2.2).
Ecological interpretation of environmental sam-
ples is only as meaningful as the samples them-
selves, so great care must be taken in planning
how and where the samples are collected. Strate-
gies for phytoplankton collection will also vary
with the dynamics of the aquatic system, which
is clearly different for standing waters (lakes and
wetlands) compared to flowing waters (rivers and
estuaries).

and location of sites across the water body, whether
these are taken at specific points or along a line (trawl
net), frequency of sampling and depth within water
column. Phytoplankton samples should be taken at
the same (or close to) sites that are used for obtaining
physicochemical lake data and may be selected on a
random basis in relation to a grid network or transect
lines (Eaton et al. , 2005) or on the basis of specific
features of the water body - for example near the inlet
or outlet of a reservoir.
Theexactsamplingscheduleemployeddependson
the overall aims and objectives of the project and can
provide information on the occurrence of planktonic
algae at various ecological levels (Fig. 2.3) - includ-
ing general phytoplankton characteristics, diversity
within the water column and small-scale patchiness
of microalgal distribution.

2.1.1 Standing water phytoplankton

General phytoplankton characteristics

Phytoplankton is normally collected at various sites
in the water body. These will normally be located in a
deeppartofthelakeandawayfromtheshore,toavoid
contamination by sediment and littoral organisms,
respectively. The strategy for phytoplankton sam-
pling in standing waters varies in relation to number

In many cases, phytoplankton sampling is carried
out simply to keep a broad ecological record of
phytoplankton populations (total biomass, species
composition, seasonal changes) present. These
parameters can provide useful information on lake