Page 99 - Freshwater-Biology-and-Ecology-Handbook

On loose riverbed substrates, leave the air flowing and move
the airlift continuously across the riverbed.

On more compacted substrates, sample in a series of short
bursts in different locations by turning the air supply on
and off and bouncing the airlift to help disturb the riverbed.
Whichever method you use, you must aim to sample the
habitats present in proportion to their cover.
Supplement the airlift sample from the main channel with a
1-minute marginal sweep (Section 7.5).
Figure 2.10
Using an airlift. DOF = direction of flow

Figure 2.11
Using an airlift in the field
7.5 Marginal sweep

A 1-minute marginal sweep using a standard pond
net always accompanies a 3-minute sweep with
a long-handled pond net or a 3-minute airlift from
sites that are too deep to wade.

The marginal sweep is for sampling the shallow margins
including emergent vegetation that is likely to be missed
in the main sample, particularly from airlift samples. It can
be done from the banks, but in large deep rivers where an
airlift is used, it may be more effective to collect the sample
from a boat. Ideally, the margins of both riverbanks should
be sampled. The 1 minute should be divided between the
different marginal habitats according to their cover.
© Judy England

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