Page 88 - Freshwater-Biology-and-Ecology-Handbook

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CHAPTER 2 4 WHEN TO SAMPLE

Three seasons are recognised by RIVPACS, which
can predict the invertebrate fauna and value of biotic
indices in any of these seasons. Samples should be
collected in one or more of these seasons.

Table 2.2
Seasons recognised by RIVPACS
Season Months

Spring March – May

Summer June – August

Autumn September – November

Because flows in the UK are greater in winter, rivers are
less amenable to invertebrate sampling then, and it can be
dangerous if flows are high. Invertebrates are less easy to
catch in high flows because they bury deeper into the riverbed.
Fortunately, higher flows offer greater dilution to pollutants.
For these reasons, scheduled river invertebrate monitoring is
not undertaken in winter.
RIVPACS cannot predict the invertebrate communities
found in winter because they are not represented in the
data from which RIVPACS is derived. If winter samples must
be compared to RIVPACS predictions for operational or
investigative reasons, those collected in December and
January should be treated as autumn samples, and those
collected in February as if they were from spring. Comparisons
of samples from winter with RIVPACS predictions will include
unquantified errors so must be treated with caution.

Samples used for the official WFD river invertebrate status
classification must be collected from both spring and the
following autumn. Other combinations, including single
seasons, can only be used to estimate the classification (for
example, to evaluate impacts of pollution or drought), but
must not be used for official reporting or the assessment of
compliance against statutory environmental objectives. This is
not only to ensure comparability between classifications (and
objectives) but also to ensure adequate precision.

88 | Freshwater Biology and Ecology Handbook
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