Page 169 - Freshwater-Biology-and-Ecology-Handbook

The UK government has set the class boundaries (Table Understanding how these indices work is important for
3.7) in statutory directions in The Water Framework Directive interpreting the WFD river invertebrate status classification.
(Standards and Classification) Directions (England and Wales) Similarly, an understanding of how the classification metrics
2015 (download from https://www.legislation.gov.uk/ of all the biological quality elements relate to each other
uksi/2015/1623/resources), and the Scottish Government enables a much better interpretation of overall biological
in The Scotland River Basin District (Standards) Directions status. WHPT ASPT and WHPT NTaxa are described in
2014 and for the Solway and Tweed, which have separate more detail in Section 2.2.
legislation as cross-border river basins, in The Solway Tweed
River Basin District (Standards) (Scotland) Directions 2014, Technical guidance for calculating these classifications is
both of which can be downloaded from https://www.gov. described in documents on UK TAG’s website http://www.
scot/publications/water-environment-legislation/ wfduk.org/ (follow the link ‘Biological Standard Methods’,
‘Rivers – Invertebrates (General Degradation)’, then select
The official definitions of each of these classifications ‘River Invertebrates WHPT UKTAG Method Statement
are in UK TAG’s (UK Technical Advisory Group) method Dec2014.pdf’ (see Figure 3.19 below).
statements, which can be downloaded from the UK TAG
website: http://www.wfduk.org/resources/category/
biological-standard-methods-201

Each river invertebrate classification metric is classified
separately, and the overall river invertebrate class is
determined by the ‘one out, all out’ principle (Chapter 1,
Section 5.1 Introduction).

Table 3.7
The UK’s official river invertebrate class boundaries
(from government directions)

WHPT ASPT WHPT NTaxa
Class boundary
(EQR) (EQR)
High/Good 0.97 0.80

Good/Moderate 0.86 0.68
Moderate/Poor 0.72 0.56

Poor/Bad 0.59 0.47
Figure 3.19
Front cover UK TAG River Assessment Methods
– Benthic Invertebrate Fauna, which describes
the UK’s WFD status classification (50)

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