Page 191 - Freshwater-Biology-and-Ecology-Handbook

3.1 Artificial substrates

The ‘artificial substrates’ methods are useful in deep and downstream sites should be as similar as possible. SAufU
fast flowing sites where there is no access for conventional are best deployed by mounting them on two bricks, to help
sampling, or where a more quantitative analysis is anchor them and prevent them from silting-up when on sand
needed. Two types of sampling device are recommended or clay river beds. Ideally, they should be tethered to the
for collecting invertebrate samples for environmental bank (perhaps from a tree) using black rope (which is less
assessment. visible than lighter colours) so that they can be retrieved,
but care should be taken to avoid areas where boats or
The first is the Standard Aufwuchs Units (SAufU) (Figure people may go. They should be left in situ for 3–4 weeks,
4.5), and the second is stone-filled mesh bags, using so they need to be hidden well. It is recommended that
cleaned stones from nearby on the same river. Both work more devices than needed are deployed in order to allow
well. SAufU are better standardised; stone bags provide for loss, damage or disturbance. Indices such as WHPT
samples that are more representative of the benthic fauna ASPT and Ntaxa may be used but not RIVPACS, as results
at the site. from artificial substrates methods are unsuitable for status
classification.
Artificial substrate methods sample a different invertebrate
community (the fouling community) to that sampled Prichard samplers are similar to stone bags, but they
directly by RIVPACS methods. Therefore it is necessary are much larger, filled with bed material from the site and
to sample both upstream and downstream of RIVPACS embedded in it, but open at the surface until the sample is
(and if possible, before and after) using the same artificial retrieved. (60) They have been designed as alternatives to
substrates method to observe an impact. Upstream and traps for sampling crayfish.

Figure 4.5
SAufU artificial substrate

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