Page 90 - Freshwater-Biology-and-Ecology-Handbook

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CHAPTER 2 5 SITE SELECTION

The following criteria must be considered when selecting monitoring sites:

Representative sites Suitability for the RIVPACS model

It is important that monitoring sites are representative of If data from the site is to be analysed by RIVPACS, for
the intended monitoring target. Sites for assessing and example if it is to be classified, it must be aligned with the
managing the quality of a whole reach or water body must parameters of the original model. The average value of
be well away from the influence of local disturbances, environmental predictor variables such as width and depth
particularly bridges, fords and other structures, and outside must be representative of the site as a whole.
the mixing zones of discharges or tributaries, because the
influence of these local pressures may mask the signal from RIVPACS is suitable only for permanently flowing
the rest of the water body. However, where the site is one streams that flow above ground and downwards to the
of a random set of sites for assessing quality over a wider sea. Standardised sampling methods for temporary and
scale, such as the Environment Agency’s River Surveillance intermittent streams are still under development, particularly
Network, it is important not to exclude such sites because for the terrestrial phases. Methods for sampling from the dry
that would bias the evaluation. The River Surveillance regions of intermittent streams, very small streams, springs,
Network sites are not used individually but together to and underground streams are given in Chapter 4. The
assess overall quality at a much wider scale. They must RIVPACS sampling methods described here can be used for
therefore cover all impacts, whether local or wide-scale. canals, ditches, drainage dykes and tidal streams but they
The network is designed to be representative of the whole are unsuitable for analysis by RIVPACS and therefore their
river network, hence its truly random site selection. WFD invertebrate status cannot be classified.

Isolated habitats

Physically isolated habitats should be avoided because
they support fewer taxa than extensive areas of the same
habitat. Their reduced diversity is likely to be misinterpreted
as an impact of environmental disturbance. For example,
an isolated shallow gravelly riffle would be unsuitable, even
though it is easier to sample and supports more taxa. If the
river is mostly deep and wide with a silt bed, the sampling
site should also be deep and wide with a silty bed. This can
be another reason for avoiding some bridges because the
stream bed near them may comprise rubble from previous
structures, and because bridges are often built where rivers
are particularly narrow or shallow. Our assessment methods,
including RIVPACS, are not able to distinguish isolated from
extensive habitats and isolated habitats are not included in
the RIVPACS reference database.

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