Page 53 - Freshwater-Biology-and-Ecology-Handbook

The main goal of a monitoring programme is Aim to avoid sites that are:
not to assess local features of a stream but to • close to artificial influences, such as dams, bridges,
gain understanding of the ecological quality of fords, weirs, piers, moorings, reinforced or artificial
a whole water body or a complete catchment. banks, and livestock watering areas. If this is not
Sampling sites should be representative of possible, the site must represent the water body
as a whole. Record any artificial influences on the
the reach being monitored and therefore field data form and take them into account in data
representative of its biota. analysis
• immediately downstream of confluences or
discharges where waters are not fully mixed
In general, monitoring sites should usually be at the lower (see Figure 1.11)
end of water bodies so that they can detect impacts from • close to the influence of in-stream lakes and
activities further upstream. However, a disadvantage reservoirs
of monitoring at the downstream end of reaches is that • on stretches subject to dredging or regular
smaller, upstream types will be under-represented, weed removal
especially head waters that are particularly sensitive to
pressure and very important as sources of recolonisation. • in isolated habitats, such as in riffles when they are
uncommon in the reach; isolation causes biological
communities to be intrinsically less diverse)
Biological samples usually require different sites to those
used for chemical monitoring. Chemical monitoring sites • on braided or divided channels – if the site cannot
tend to be on bridges for convenience and ease of access. be located elsewhere, such as on a fully braided
However, they should be avoided for biological sampling river, sample within the largest natural channel
as they will influence the sample because of shading, • predominantly on bedrock, as it is difficult to
because of rubble and other debris below the bridge, and sample the invertebrate fauna.
because bridges are often located where the river channel
is narrowest and therefore not typical of the water body as
a whole. The physical characteristics of the sampling site
should be as natural as possible so that the samples are
representative of the water body, and the biota reflects the
pressures in the water body as a whole rather than those in
the immediate vicinity of the monitoring site.

Mixing zone

Figure 1.11
Always ensure that you sample downstream from the mixing
zone, where pollutants and receiving water are well mixed. It is
rare for the mixing zone to be visible, as it is in this photograph.

The ‘sampling area’ from which the sample is collected should be within a larger ‘survey area’ with similar characteristics.
The sampling area is the spot where the biological sample is taken and should be representative in order for the stream
reach to be assessed. The sampling area must reflect the habitat composition of the survey area. The size of the sampling
area depends on the stream width and the quality element being sampled. The survey area might cover a section of several
hundred metres of stream length up to a complete catchment area of a small stream for which the sampling site should be
representative. This ensures that the sampling area is not an isolated habitat, enables a new sampling area to be used if part
of the site is damaged, and minimises the effect of inaccurate relocation of the site by a different surveyor.

It is also useful to have biological monitoring sites close to sites for monitoring other elements including chemistry and
hydromorphology so that they can be analysed together.

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