Page 176 - Freshwater-Biology-and-Ecology-Handbook

CHAPTER 3 5 – 6 5

INTERPRETING THE RESULTS OF

WFD RIVER INVERTEBRATE STATUS

CLASSIFICATION

This section provides some reminders for anyone data can simply mean that you are at the far north, south,
interpreting the UK’s WFD river invertebrate status east or west of the country, beyond the range of RIVPACS
classification beyond face value, giving a few tips to check reference sites, so they are generally not a concern.
before engaging in expensive remediation work, plus some Warnings that other limits have been exceeded indicates that
extra diagnostic clues to pressures. those environmental parameters are beyond the conditions
covered by the RIVPACS model. Exceeding the failure limits
The classification can be imprecise. Always check is more serious because it means that your environmental
the relative probabilities of belonging to each general input data exceeds the values found anywhere in the UK, so it
degradation status class as well as the probability of the always indicates an error.
face value class. That will also show you the likelihood
of being better or worse than the face value class or the Comparing the classifications from WHPT ASPT and
environmental quality objective. You should not implement WHPT NTaxa provides some basic diagnostic information.
an expensive restoration programme on the basis of a face If WHPT ASPT class is Good or High but WHPT NTaxa
value class or likelihood of failure to meet the objective class class is poorer, there may be toxic pollution or habitat
that has comparatively low probability. degradation. If WHPT ASPT class is not Good, there may
be organic pollution (still the most common environmental
Always check the RIVPACS suitability code. That tells you pressure) but it could also be caused by any of the pressures
how well the site fits the RIVPACS model (according to its that WHPT ASPT responds to, including any that affect the
environmental predictor data) and therefore how reliable oxygen concentration or the ability of animals to breathe,
the classification is, regardless of the probabilities of class. such as fine silt. More information about the diagnostic ability
Never implement a restoration programme solely on the of classifications from the individual indices is provided in
basis of a river invertebrate classification with low suitability. Section 2.2. When WHPT NTaxa is very small, the precision
Always check the environmental input data for errors if you of WHPT ASPT and many other biotic indices will also be
get a poor suitability code. low. The diagnosis provided by the different classifications
is indicative and you must undertake a more detailed
Check the error messages produced by RICT2. Exceeding investigation to identify pressures more reliably before
a warning threshold can indicate an error in your implementing measures to restore quality.
environmental input data. Warnings caused by location

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