CEN/TR 16151:2011

SLOVENSKI STANDARD
01-junij-2011
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Water quality - Guidance standard on the design of Multimetric Indices
Wasserbeschaffenheit - Anleitung zur Planung und Erstellung Multimetrischer Indices
Qualité de l'eau - Norme de recommandations relatives à la conception des indices
multimétriques
Ta slovenski standard je istoveten z: CEN/TR 16151:2011
ICS:
13.060.45 Preiskava vode na splošno Examination of water in
general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

TECHNICAL REPORT
CEN/TR 16151
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
April 2011
ICS 13.060.45
English Version
Water quality - Guidance on the design of Multimetric Indices
Qualité de l'eau - Lignes directrices pour la conception des Wasserbeschaffenheit - Anleitung zur Planung und
indices multimétriques Erstellung Multimetrischer Indices

This Technical Report was approved by CEN on 27 December 2010. It has been drawn up by the Technical Committee CEN/TC 230.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2011 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 16151:2011: E
worldwide for CEN national Members.

Contents Page
Foreword .3
Introduction .4
1 Scope .5
2 Terms and definitions .5
3 Principle .6
4 Procedure .7
4.1 General .7
4.2 Selection of Candidate Metrics .8
4.3 Exclusion of redundant metrics .8
4.4 Definition of Upper and Lower Anchors .8
4.5 Transformation into a 0 to 1 score .9
4.6 Selection of core metrics .9
4.7 Combination of Core Metrics to a Multimetric Index indicating a single stressor or
indicating general degradation (general multimetric approach) .9
4.8 Combination of Core Metrics to a Multimetric Index separating the impact of different
stressors . 10
Annex A (informative) Examples for metrics used to assess individual Biological Quality
Elements, assigned to metric types. 11
Bibliography . 12

Foreword
This document (CEN/TR 16151:2011) has been prepared by Technical Committee CEN/TC 230 “Water
analysis”, the secretariat of which is held by DIN.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
Introduction
Multimetric Indices are among the commonly used tools for classification of the quality of fresh water and
brackish water ecosystems (rivers, lakes, transitional waters, wetlands). A Multimetric Index combines several
individual metrics, the results of which are finally combined into a Multimetric result. Thus Multimetric Indices
integrate several attributes of a community (“metrics”) to describe and assess condition. Different categories
of metrics (e.g. taxa richness, share of sensitive and tolerant species, trophic structure) reflecting different
environmental conditions are combined into one Multimetric Index.
Multimetric Indices can be applied to different aquatic ecosystems (rivers, lakes, transitional waters, wetlands)
and to different Biological Quality Elements (fish, benthic invertebrates, macrophytes, phytoplankton,
phytobenthos). They are flexible in terms of the composition of metrics, since different metrics are suited for
the assessment of different ecosystems or different stressors.
In recent years, a wide variety of Multimetric Indices has been developed and is now being applied,
particularly for the purpose of implementing the Water Framework Directive. It can be expected that many
existing Multimetric Indices will be adapted and many new ones will be developed within the next years. To
enhance comparability between Multimetric assessment systems the procedure of developing and applying a
Multimetric Index is described.
1 Scope
This document describes methods for developing and applying Multimetric Indices used for assessing rivers,
lakes, transitional waters or wetlands. It is suitable for use with data on fish, benthic invertebrates,
macrophytes, phytoplankton, and phytobenthos.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
Anchors (Upper and Lower Anchors)
values of a metric, which are empirically set and defined as “1” (Upper anchor) and “0” (Lower anchor),
respectively, for transferring a metric’s result into a 0 to 1 score
NOTE The Upper Anchor relates to the reference value (i.e. the metric’s value under reference conditions). The
Upper Anchor can be calculated from the median or mean of reference samples or by other appropriate statistical
methods as described in 4.3.
The Lower Anchor is related to the lower limit of the metric’s value under the worst ecological quality conditions.
2.2
fresh water or brackish water type (river type, lake type, transitional water type)
division into an ecologically meaningful entity of sites with limited biotic and abiotic variation and a
recognisable discontinuity with other types
NOTE Fresh water or brackish water types serve as “units“, to which an assessment system can be applied.
2.3
metric
measurable part or process of a biological system empirically shown to change in value along a gradient of
human influence [2]
NOTE It reflects specific and predictable responses of the community to human activities, either to a single factor or
to the cumulative effects of all events and activities within a watershed.
2.4
metric type
metrics addressing comparable aspects of a community, regardless of the stressor to which the metrics are
responding
NOTE The following metric types can be distinguished (see Annex A):
− composition / abundance metrics: all metrics giving the share of a taxon or taxonomic group in relation to the total
number of individuals counted; all metrics giving the abundance of a taxon or taxonomic group; metrics
comparing reference and observed taxa (e.g. similarity indices);
− richness / diversity metrics: all metrics giving the number of taxa within a certain taxon (including the total number
of taxa), all diversity indices;
− sensitivity / tolerance metrics: all metrics giving the ratio of taxa sensitive and insensitive to stress in general or to
a certain stress-type, either using presence/absence or abundance information;
− functional metrics: all metrics addressing the characteristics of taxa other than their taxonomic definition
(biological or ecological traits, ecological guilds): feeding types, habitat preferences, ecosystem type preferences,
current preferences, life-history parameters, body-size parameters; they can be based on taxa abundance or
richness.
2.5
Multimetric Index
combination of the results of three or more metrics
2.6
stressor
category of direct or indirect human impact to a fresh water, which potentially influences the composition and /
or abundance of stream biota
NOTE The following stressors can be distinguished:
− organic pollution: organic matter input induced by human activities;
− eutrophication: nutrient input induced by human activities;
− acid stress: permanently or temporarily decreased pH value due to human activities;
− temperature stress;
− toxic stress: effects of toxic contaminants released by human activities;
− degradation in stream morphology: bed and bank alteration, habitat degradation, riparian land use, straightening,
migration barriers, siltation;
− hydrological stress: alteration of flow regime, e.g. residual flow, pulse releases;
− general degradation: simultaneous and inseparable impacts of more than one stressor.
2.7
stressor gradient
set of sites of a fresh water ecosystem type with a varying intensity of a stressor
3 Principle
Two ways of calculating Multimetric Indices can be distinguished: the “general approach” and the “stressor-
specific approach”.
In the “general approach”, various metrics are calculated from a taxa list. The metric results are individually
compared to the respective metric values under reference conditions. From this comparison, a score for each
metric is determined. These scores are finally combined into a Multimetric Index (Figure 1).
The “stressor-specific” approach sorts a suite of metrics according to their ability to detect a certain stressor.
Thus, the scores of the metrics addressing a single stressor are first combined into a value reflecting the
intensity of this stressor. The assessment results for all stressors are finally combined into the Multimetric
Index (Figure 2).
Both ways of calculating Multimetric Indices may have advantages in certain situations: The “general
approach”, carefully applied, provides an overview of a water body’s status and is, thus, mainly suited if the
specific effects of individual stressors on the targeted organism group are not known in detail. It can, for
example, be applied for the general ecological quality assessment and for intercalibration purposes. The
“stressor specific approach” can only be applied if precise information on the effects of different stressors (e.g.
acidification, organic pollution) on the targeted organism group are known and it is most suited for
investigative monitoring purposes, tailored towards the identification of alteration causes.
The results of a Multimetric Index can be viewed at different levels: at the upper level there is the Ecological
Quality Class, at the second level (in case of the stressor specific approach) are the results of the stressor
specific modules (quality classes “organic pollution” and “stream morphology degradation” in Figure 2) and at
the third level the results of the individual metrics are produced.
Figure 1 — The “general approach” of multimetric assessment

Figure 2 — “Stressor-specific approach” of multimetric assessment
4 Procedure
4.1 General
The procedure of developing a Multimetric Index is composed of the following steps:
 Selection of Candidate Metrics;
 Exclusion of Redundant Metrics;
 Definition of Upper and Lower Anchors;
 Transformation of Core Metrics into a 0 to 1 score;
 Selection of Core Metrics;
 Combination of Core Metrics to a Multimetric Index.
4.2 Selection of Candidate Metrics
Select only those metrics showing a quantitative dose-response change across a stressor gradient that is
reliable, interpretable and not dispersed or obscured by natural variation. Selecting Candidate Metrics consists
of the following steps:
a) Compilation of a data set of the freshwater type the Multimetric Index will apply to. This dataset shall
include data on the Biological Quality Element that the Multimetric Index will use, for different sites
covering the widest range of alteration.
b) If the required information is available, metrics of all metric types should be calculated (composition /
abundance metrics, richness / diversity metrics; sensitivity / tolerance metrics; functional metrics).
c) Definition of a stressor gradient within the dataset by:
1) using abiotic data on the individual sites, describing the impact of a single stressor (e.g. data on
BOD or on oxygen content for a Multimetric Index addressing organic pollution;
2) using abiotic data on the individual sites, describing the impact of general degradation (e.g. data on
catchment land use; hydromorphological modification and water pollution combined);
3) defining a gradient within an ordination space of the taxonomic composition of th
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