Page 228 - Freshwater-Biology-and-Ecology-Handbook

CHAPTER 5 3.1.8 – 3.19 3.1.8 AWIC (Acid Water

Indicator Community)
indices

AWIC is a diagnostic index sensitive to acidification in British
rivers. It responds to base-flow and storm-flow pH and acid
neutralising capacity (ANC). WFD AWICsp is a particular form
of AWIC that is used for status classification and is described
in Chapter 3 Section 6.

AWIC – Acid Water Indicator
Community index

This index is used to assess the impacts of acidification
and is the basis for the UK’s status classification for
streams subject to acidification from acid deposition.

The first version of this index was the family-level AWICfam:
Davy-Bowker et al. (2005), (83) Ormerod et al. (2006). (84) For
species-level data with abundance data, use WFD AWICsp
– see Chapter 3 Section 6 (McFarland 2010) (85) and
WFD-UKTAG (2014) (86) – which is also used for determining
acidification status class. WFD AWICsp was preceded
by AWICsp (Murphy 2009, (87) Murphy et al. 2013, (88) and
McFarland 2010 (85) ) which is based on presence-only
data and you can use it if you do not have abundance data.
However, it must not be used for status classification.
AWIC responds to acidification from both acid deposition
and acid mine drainage, and it can be impossible to
differentiate them.

The species-level AWICsp index values were derived
empirically from a multivariate ordination based on a data
set of 197 sites to quantify variation in macroinvertebrate
assemblages, and to identify which environmental
variables best described the ordination. Taxa were ranked
along an acid–base gradient, having first considered the
merits of factoring out confounding variation from natural
environmental factors.

Index values for each species (integer values from 1–9)
were based on the percentage distance along this
canonical correspondence analysis (CCA) axis.

The resulting AWICsp was tested using an independent
data set. This was similar to the approach used to derive
the CoFSI index of fine sediment (Section 3.1.14) and the
MetTol index (Section 3.1.17). WFD AWICsp (Chapter 3
Section 6) was derived from this index.

228 | Freshwater Biology and Ecology Handbook
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