Page 43 - Freshwater-Biology-and-Ecology-Handbook

When considering the causes of biological failure of a water body
(Figure 1.6, Box 1), we generally take four things into account:

Our professional The existing pressures The tools and Existing biological data
knowledge of the in the water body and methods that we (including external
response of biology wider catchment, use to diagnose the data), its trends and its
to pressures taking local knowledge causes of biological statistical associations
into account pressure with pressures

These enable us to identify failures to meet objectives and
to infer the causes of failures (Fig 1.6, Box 2). When we do
this, we also assess whether the level of evidence linking the
pressure with the biological failure is sufficient to support
action (Fig 1.6, Box 3) as set out in the guidance on ‘Levels of
evidence for completing investigations and selecting measures’.
Where there is sufficient evidence, the next steps, eg an
investigation to determine the source of the pressure and/or
implementing measures, can proceed. The pressure might be
high phosphate from agriculture and the proposed action may
be revised guidance on fertiliser application. However, if the
level of evidence does not support action, ie there is insufficient
evidence linking the pressure to the biological impact to justify
action, then we conclude that we can’t infer the cause of the
failure with sufficient confidence (Fig 1.6, Box 6).
If we can’t infer the likely cause of failure based on the initial
assessment (Fig 1.6, Box 2), then we need to judge if the current
data is adequate for the application of the diagnostic tools or to
apply professional judgement (Fig 1.6, Box 4). Where the data is
inadequate, we then gather more or different data (Fig 1.6, Box
5). If the data is sufficient to apply the tools but we can’t infer
what causes the failure (Fig 1.6, Box 6) our next step depends on
the level of certainty associated with the cause of failure.

Where we are uncertain about what causes the failure, we
need to explore the situation by gathering and assessing more
extensive data (Fig 1.6, Box 7). This might include increasing the
number of biological elements sampled at the water body, and/
or it may include collecting more data on pressures.

Where we have a good idea of what causes the failure
(Fig 1.6, Box 8), we would normally intensify monitoring, focusing
on the biological elements most likely to be affected by the
pressure in question (Fig 1.6, Box 9). For example, where the
suspected pressure is flow, invertebrate analysis might be taken
to species (rather than family) level to improve the strength of
evidence linking the pressure to the failure. Occasionally, we
might undertake an experimental application of a measure to
reduce the pressure to demonstrate if this improves the biology
(ie ‘Adaptive Management’) (Fig 1.6, Box 10).

Our knowledge of biological responses to pressures and our
diagnostic toolkit will improve further as we repeat this process
over time and at multiple water bodies.

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