Page 168 - Freshwater-Biology-and-Ecology-Handbook

CHAPTER 3 4.1 The properties of the biological communities representing The metrics that we use to calculate the classification
High, Good and Moderate status in rivers according to its
must reflect all aspects of those definitions with sufficient
benthic invertebrate fauna are described in the normative
precision to differentiate the classes.
definitions in Annex V of WFD (see Table 3.6 below).

Table 3.6
Normative definitions for High, Good and Moderate invertebrate status in rivers (from WFD Annex V 1.2.1)

Status Normative definition

The taxonomic composition and abundance correspond totally or nearly totally to
undisturbed conditions.
The ratio of disturbance-sensitive taxa to insensitive taxa shows no signs of alteration
High
from undisturbed levels.
The level of diversity of invertebrate taxa shows no sign of alteration from undisturbed
levels.
There are slight changes in the composition and abundance of invertebrate taxa from
the type-specific communities.
Good The ratio of disturbance-sensitive taxa to insensitive taxa shows slight alteration from
type-specific levels.
The level of diversity of invertebrate taxa shows slight signs of alteration from
type-specific levels.

The composition and abundance of invertebrate taxa differ moderately from the
type-specific communities.
Moderate Major taxonomic groups of the type-specific community are absent.
The ratio of disturbance-sensitive taxa to insensitive taxa, and the level of diversity, are
substantially lower than the type-specific level and significantly lower than for Good status.

These class descriptions provide the anchors for the established systems by modifying them to comply with the
boundary-setting protocol and links to the concept of main concepts demanded by the directive. This is why we
reference and type-specific communities (Chapter 1 continue to use biotic indices that relate to the sensitivity
Section 5.7). of invertebrates to pressure. The strength of large existing
data sets helped smooth the transition to WFD, but at the
The normative definitions do not relate to particular types cost of not allowing for the development of methods to
of pressures, only to the invertebrate communities. The recognise new environmental challenges.
classification metrics could be based simply on the degree
to which the invertebrate community deviates from the In the UK, we use a combination of WHPT ASPT and
reference community in terms of its composition and WHPT NTaxa that together respond to almost all
abundance, using a similarity index. In the author’s view, pressures (see Section 2.2). Invertebrate communities
that approach may be the best. However, when the Water respond to the integrated effect of all pressures, both
Framework Directive was implemented, a more iterative natural and anthropogenic. The result of this is that all biotic
approach was taken and all Member States, including the indices co-vary to an extent and all respond to pressures
UK, were allowed to retain continuity with their existing and other than those that they are designed to reflect.

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