Page 60 - Freshwater-Biology-and-Ecology-Handbook

CHAPTER 1 5.3 5.3 Ecological Status

Ecological status is an expression of the quality of the structure and

functioning of surface water ecosystems as indicated by the condition
of a number of ‘quality elements’.

The biological quality elements drive ecological status The WFD provides descriptive ‘normative definitions’ for
assessment. The other quality elements are supporting high, good and moderate status of all the ecological quality
factors. They are environmental parameters that, in the elements. Figure 1.16 provides these important definitions,
right amounts, are essential to biological communities. and specific text from the WFD is included here.
Their class boundaries are set at values that ensure
good or better biological status.

Element High Status Good Status Moderate Status

General There are no, or only very minor, anthropogenic The values of the The values of the biological
alterations to the values of the physico-chemical biological quality quality elements for the
and hydromorphological quality elements for the elements for the surface water body type
surface water body type from those normally surface water body deviate moderately from those
associated with that type under undisturbed type show low levels normally associated with the
conditions. of distortion resulting surface water body type under
from human activity, undisturbed conditions. The
The values of the biological quality elements for but deviate only slightly values show moderate signs of
the surface water body reflect those normally from those normally distortion resulting from human
associated with that type under undisturbed associated with the activity and are significantly
conditions, and show no, or only very minor, surface water body more disturbed than under
evidence of distortion. type under undisturbed conditions of good status.
conditions.
These are the type-specific conditions and
communities.

Figure 1.16
Normative definitions of ecological status classifications
(from the WFD). See also the bullet points below.

• Waters achieving a status below moderate shall be
classified as poor or bad.
• Waters showing evidence of major alterations to the
values of the biological quality elements for the surface
water body type and in which the relevant biological
communities deviate substantially from those normally
associated with the surface water body type under
undisturbed conditions, shall be classified as poor.
• Waters showing evidence of severe alterations to the
values of the biological quality elements for the surface
water body type and in which large portions of the
relevant biological communities normally associated
with the surface water body type under undisturbed
conditions are absent, shall be classified as bad.

As mentioned previously, there are five classes of ecological
status: high, good, moderate, poor and bad. The Directive
requires that the overall ecological status of a water body
be determined by the results for the biological or physico-
chemical quality element that has the worst status class
Mafly larave like this Ecdyonurus, are often (ie the quality element worst affected by human activity).
associated with high status water bodies.
This is called the ‘one out – all out’ principle.

60 | Freshwater Biology and Ecology Handbook
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