Sampling, Biomass Estimation and Counts of Freshwater Algae - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 46

Littoral zone

(a) GENERAL LAKE
ECOLOGY
Multiple sites

A B

Sampling site

C

Central deep
region

Aerial view of lake

Figure 2.3 Strategies for sam-
pling lake phytoplankton. Different
strategies provide information on:
(a) General lake ecology - sam-
ples from different pelagic sampling
sites (A, B, C) and littoral zone.
(b) Diversity within the water col-
umn - depth samples, sedimenting
algaeandintegratedsamples.Vertical
zonation - Epi (epilimnion), M (met-
alimnion) and Hypo (hypolimnion).
(c) Microecology of phytoplankton,
looking at small scale distribution,
patchiness and associations. Analysis
of microsamples and high-resolution
in situ monitoring of phytoplankton
biomass.

Lake surface algae

Epi

Integrated
depth sample

M

Sediment trap

(c) MICRO-ECOLOGY
Small-scale distribution
of algae. Diversity
within local populations.

Hypo

Discrete depth
samples

Sediment

(b) DIVERSITY W ITHIN
WATER COLUMN

samples), to monthly (general seasonal progression)
and higher frequencies (monitoring rapidly occurring
lake changes). An intensive sampling programme,
involving collection once or twice a week (Tittel
et al ., 1998), is necessary to capture detailed popula-
tion dynamics and to quantify short-term fluctuations
in phytoplankton abundance and biomass.

entering an overwintering phase (see Section 2.7.1).
Other algae, particularly colonial blue-greens and
dinoflagellates, periodically enter the hypolimnion
as part of their diurnal cycle, taking up inorganic
nutrients at a time of year (in many lakes) when
the epilimnion has been largely stripped of soluble
nitrates and phosphates. Collection of algal samples
at specific points in the water column (Fig. 2.3b)
can provide dynamic information on all of these
processes and may involve special collecting devices
such as depth samplers (Fig. 2.5) and sedimentation
chambers.

Diversity within the water column

Vertical separation of algal biomass into actively
growing photosynthetic populations (high light:
epilimnion) and non-photosynthetic cells (low light:
hypolimnion) represents one of the broad ecological
sub-divisions within the pelagic ecosystem. Cells
within the hypolimnion may be sinking in the water
column by passive sedimentation - including cells
undergoing senescence (see Section 2.6.2) and cells

Small-scale characteristics and associations
of phytoplankton

Localised distribution and associations of phyto-
plankton cells/colonies within the water column