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CHAPTER 3 2.3 – 2.5 2.3 Comparison of BMWP

and WHPT

WHPT ASPT is on the same scale as WHPT BMWP. The only
difference, apart from improved accuracy and precision, is the greater
sensitivity of WHPT ASPT to mild enrichment that affects abundances
but not species composition. WHPT NTaxa responds to the same
environmental pressures as BMWP NTaxa but it is not on the same
scale because it is based on a greater number of taxa (106 taxa in
WHPT and only 82 in BMWP). WHPT includes more families of Diptera,
and the constituents of composite families in BMWP are treated as
distinct families in WHPT.

2.4 Calculating WHPT indices

For status classification, WHPT must be calculated at RIVPACS
Taxon Level 2 (ie including families not included in BMWP), with
BMWP composite taxa separated into individual families and using
abundance-related index values. This is erroneously termed ‘WHPT
abundance-weighted with distinct families’ in RIVPACS (River
Invertebrate Prediction and Classification System) and RICT (River
Invertebrate Classification Tool): WHPT does not use abundance
weighting but gives independently defined index values for different
abundances of each taxon (Section 2.2). If you do not have abundance
data, or only have data for BMWP taxa including composite families,
you can still estimate WHPT, but not for status classification.
Figure 3.4
Environment Agency guide to WHPT

A guide to WHPT (Figure 3.4) and an Excel spreadsheet for calculating it (Figure 3.5) can be downloaded from the RIVPACS/
RICT methods web page https://www.fba.org.uk/rivpacs-and-rict/rict-rivpacs-user-guides
Beware that WHPT was known as ‘revised BMWP’ in early reports such as Davy-Bowker et al. (2008) on RIVPACS
development, (34) but was changed to WHPT to avoid confusion with earlier revisions of BMWP described in Walley & Hawkes
(1996 and 1997). (42) (43)

Figure 3.5
Screenshot of part of the Excel calculator tool for WHPT indices

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