Environmental Engineering Reference
In-Depth Information
Knowledge transfer, new indices and uncertainty
Due to its comprehensive nature, covering a wide range of water body types and
biological quality elements, the WFD has precipitated an unprecedented develo-
pment of new bioassessment tools across the EU. This process of development
has benefited greatly from the knowledge gained through existing tools such as
RIVPACS. Correspondingly, existing tools have been enhanced further to deal
with the issues raised by the WFD. Following the move towards the sustainable
use of water resources, many new indices are being developed for pressures
other than sewage pollution, including, for the first time, indices to assess
pollutants from primarily industrial sources. Examples include pH, heavy
metals, thermal pollution and pesticides, the consequences of industrial and
intensive agricultural processes. Rather than relying on expert judgement, as
had been done previously (e.g., BMWP), new objective statistical techniques,
such as artificial intelligence (e.g., Walley & O'Conner
2001
) and partial ordina-
tion (e.g., Davy-Bowker et al.
2005
) are being used to establish the response of
taxa to specific stressors. By removing the influence of variables that character-
ise river type, it is possible to indicate the response of the taxa to the gradient of
stress that is of interest; the rank order of sensitivity and the tolerance of taxa
can be used to identify the taxa most likely to be impacted first, and the point of
of this objective statistical approach is the Acid Water Indicator Community
(Davy-Bowker et al.
2005
), thus enabling the effects of low pH to be assessed. This
index is a considerable improvement on previous attempts (Rutt et al.
1990
).
Tests indicate that AWIC has general applicability and compares favourably
with direct pH measurement, where annual samples at fortnightly monthly
intervals are typically required to estimate mean pH with comparable precision
to a single AWIC sample (Ormerod et al.
2006
). As with all measures of condition,
the precision of the measure used has great implications in terms of confidence
in the assessment, and the cost involved in achieving that level of confidence.
Irrespective of the measure used, in comparing a test site to reference condi-
tion an environmental quality ratio (EQR) is derived from observed/expected
scores, which ranges from 0 to 1. For reporting, this range is divided into five
quality classes, namely high, good, moderate, poor and bad, and member states
must report the proportion of water bodies in each of these classes, together
with the confidence of the assessments. Any assessment is intended to repre-
sent the status of the water body as a whole over a period of time, but is
obtained by sampling/surveying one or more biological quality elements at
one or more spatial locations within the water body at one or more points
in time during the period for which the assessment is intended to apply. The
results of all bioassessment techniques are influenced by variation in the
observed fauna, which affects the certainty of the estimate of quality.
