Environmental Engineering Reference
In-Depth Information
taxa recorded (ASPT) which, together with the number of scoring families
(Ntaxa), was adopted as the standard measures of quality.
Whilst most biomonitoring techniques were developed based on the
response of invertebrates, other biological groups were incorporated into some
systems. In the USA, Patrick et al. (
1954
) developed a methodology based on
the structure of diatom assemblages, and European workers developed ideas
from the saprobic system using algae (Kelly
1998
). The Quality Rating System
(also known as the 'Q-Value' system), which has been in use in the Republic of
Ireland since 1970 (Flanagan & Toner
1972
), uses a combination of benthic
algae, macrophytes and invertebrates. As well as having different sensitivities
to toxins (particularly herbicides, but also acidity, heavy metals and other
pollutants), phototrophs respond readily to nutrient pollution (Kelly
1998
;
Holmes et al.
1999
) and, thus, are better capable of detecting nutrient impacts
than invertebrates where any effect is indirect via the effects on phototrophs.
At the other end of the food web, fish are particularly sensitive to organic and
inorganic materials that bioaccumulate (e.g., mercury, dioxins, radionucleo-
tides), and growth anomalies (deformities, eroded fins, lesions and tumours)
can be used to detect specific toxins, as well as indices based on community
integrity (e.g., Index of Biotic Integrity (Fausch et al.
1990
;Scardiet al.
2006
)).
RIVPACS and the reference condition approach
Despite continued improvements in quantifying the response of invertebrates
and other biological quality elements to pollution, none of the above systems
confronted the fundamental problem that physical and chemical characteristics
of rivers vary naturally. Different rivers contain different fauna and flora and the
likelihood of capture of a taxon at an unpolluted site is largely dependent upon
the natural environmental character of that site. As many of the characteristics
of the taxa tolerant of pollution are associated with low oxygen stress, sluggish
rivers have a fauna that produces a low score even where sites are unpolluted.
As a consequence, the practical application of early approaches often relied
heavily on expert judgement to provide an assessment of the deviation from
the expected community and, thus, the extent of pollution. By adopting the
'reference condition' approach, the River InVertebrate Prediction And Classifica-
tion System (RIVPACS) represented a major step forward in the bioassessment
of rivers (Wright et al.
1984
). In this system, it was assumed that in order to judge
the impact of pollution on the fauna of a site, that site should be compared with
the fauna of similar sites that are not subject to any apparent environmental
stress. These sites are called reference sites. In this way, site quality is measured
as a ratio, the observed/expected score, where the observed score is that of the
test site and the expected score is that predicted by RIVPACS based on the fauna at
similar reference sites. In RIVPACS the test site is matched to the reference sites
by the pollution insensitive physical, chemical and geographical characteristics
of the site.
