Page 56 - Freshwater-Biology-and-Ecology-Handbook

CHAPTER 1 5.1 5.1 Introduction of water classification and management. It ensures

In order to assess and report the quality of surface waters it
is essential to develop a method of comparing water bodies
that all the quality elements needed to provide for a
balanced ecosystem are in place within a given class.
in a consistent and transparent way that is easy for anyone
However, it causes difficulty because as more elements
to understand. This is known as classification. Knowledge
of compliance against classifications drives the river basin
misclassification for purely statistical reasons caused by
planning process and is used to target investment to meet
errors being additive. This tends to give a pessimistic view
the agreed objectives. are considered, the greater the risk of a downgraded
of quality. Also, improvements in individual elements may
The classification process results in each surface water be masked by failures of other elements. For example, the
body being assigned a status class. The WFD uses a five- biological quality may have improved due to pollution control
class system for each surface water type. These status actions, but one or more chemical elements may have failed,
classes are termed: high, good, moderate, poor, and bad. leading to an overall failure of good status. This is shown
Each class represents a different degree of degradation schematically in Figure 1.13.
from human interference.
Chemical status is based on the concentrations of priority
Surface water quality is expressed as Chemical Status substances. There are European standards for all priority
and Ecological Status. substances. Chemical status can be good or bad.

The Directive uses the term ‘quality elements’ to refer to Ecological status is based on:
the different indicators of ecological quality that comprise • biological quality elements
its ecological status classification scheme, and different • chemical and physico-chemical quality elements that
chemicals that comprise its chemical classification scheme. support the biological elements
Each quality element contributes to status according to • pollutants being discharged in significant quantities,
the ‘one out, all out’ principle, in which overall status is which are referred to as ‘specific pollutants’
deemed to be that of the individual element indicating the • hydromorphological quality elements comprising
worst class. ‘One out, all out’ is an important principle hydrological and morphological elements.

Ecological Status Surface Water
Status
Biological quality elements Invasive
Species
H H H H H H
G G G G G G H
M M M M M M G
P P P P P P
B B B B B B
Worst class Worst class
Physico-chemical elements
H
H H H H H H
G High
G G G G G G Worst class M
M M M M M M Good
P
Hydromorphological quality B Moderate
elements Worst class Poor
H H H H H H Bad
G G G G G G Worst class
Specific pollutants with UK EQS
G H/G
G G G G G G
F F F F F F Worst class F M

Chemical Status
Priority Substances and Other
Pollutants with EU EQS Good H/G
G G G G G G Worst Failing to achieve good M
F F F F F F class

Figure 1.13
Schematic representation of how results for different quality elements are combined to classify ecological
status, chemical status and overall surface water status under the WFD, based on ‘one out, all out’. Note that
only the biological quality elements define poor and bad status. (After a diagram produced by Peter Pollard)
56 | Freshwater Biology and Ecology Handbook
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