Sampling, Biomass Estimation and Counts of Freshwater Algae - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 88

In the laboratory, samples were allowed to settle
for 24 h. The supernatant was then removed and
sedimented algae were initially examined live.

typically results in the detachment of fragments of
intact periphyton community attached to a base of
organic debris that covered the stone (Fig. 2.23).
Attached algae can also be sampled by taking an
open-ended tube (2 or 4 cm in diameter, about 10
cm long), attaching a small ring of sponge rubber to
one end of the tube and pressing the tube, sponge end
down, firmly onto the surface of the stone or rock
being sampled. Insert a stiff brush down the tube and
brush the surface of the stone to dislodge any algae
living there. Remove the brush and now suck up the
dislodged algae through a pipette and transfer to a
sample bottle. As long as all of the dislodged material
is sucked up then, knowing the area of the stone that
has been brushed, a quantitative estimate of the popu-
lations present can be made. These epilithic commu-
nities are typically stratified, so different degrees of
rubbing or scraping can remove different algal layers.

Algae were then chemically processed (see also
Section 2.5.2) to reveal frustule surface ornamen-
tation. Samples were oxidised in a mixture of
concentrated sulphuric acid, potassium perman-
ganate and oxalic acid, then mounted in Naphrax©.
Diatoms (cleaned frustules) were identified under
oil immersion at ×1000 magnification. To ensure a
statistically valid count for calculating bioindices,
between 200 and 250 frustules were identified for
each sample.

The above protocol is based on taking diatoms
from a single habitat (boulders) within a reach of the
river. This ensures comparability between analyses
and is an efficient means of summarising key aspects
of the benthic algal community for use with European
Water Framework Directive (WFD; European Union,
2000) legislation. The above protocol has led to the
development of European standards for the collection
and analysis of benthic material from rivers (CEN,
2003, 2004). A similar restricted habitat (stones
and macrophytes) protocol has been proposed for
shallow-water sampling in lakes (King et al ., 2006).

Standard protocol for epilithic algae Where
algae are being sampled as bioindicators for environ-
mental monitoring, a standard protocol needs to be
implemented to ensure comparability between dif-
ferent collection sites. This is required, for exam-
ple, where benthic diatoms are being sampled and
bioindices calculated to assess river quality (Sec-
tion 3.4.2). The system used by Kelly et al . (1995),
adapted from Round (1993), is as follows:
Five different boulders were chosen at any one
river sampling site, taken from five different posi-
tions within a 10-m reach. As far as possible, boul-
ders (

Loose sediments Algae present on sand (epipsam-
mic) and mud (epipelic) surfaces can usually be col-
lected by taking a portion of sediment with a scoop
and transferring this to a wide-necked sample bottle.
Algae growing on loose sediments may be dis-
turbed and mixed with the sediment whilst being col-
lected, so it is important to make sure that only the
thin surface layer of sediment is scooped up when
collecting the sample. A sub-sample of the sediment
and algae can either be directly observed under a
microscope or algae within the sample can be con-
centrated. This can be achieved by placing the sample
in a Petri dish and allowing it to settle for 12-24 h
in the light. During this period, many (but not all)
benthic algae are able to migrate through the sedi-
ment towards the light, becoming concentrated in the
surface layer. These surface algae can be collected
by placing a small piece of microscope lens tissue on
the mud surface and left for a few hours in the light.

256 mm) were selected that were free of
filamentous algae. In lowland streams, where this
was typically not possible, diatom material was
removed from parts of the boulder free of such
contaminants.

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Selected boulders were washed briefly in stream
water at the site to remove lightly attached stream
organisms and then diatoms removed to provide a
composite sample.

Diatoms were removed by scraping the upper sur-
face of the boulder with a stiff toothbrush, then col-
lecting the epilithon, suspended in stream water, in
a 250-ml sample bottle.