Environmental Engineering Reference
In-Depth Information
Beta-mesosaprobic ( b ) oxidation processes predominate
Oligosaprobic (o)
Complete oxidation
The saprobic system was refined by various workers through the early
twentieth century and was formalised in the Prague Convention of 1966
(Sl´deˇek 1967 ). With further refinements (see Rolauffs et al. 2003 ), the index
still continues to be used in several European countries, in two ways that differ
in calculation method (i.e., the formula of Pantle and Buck ( 1955 ) or the
formula of Zelinka and Marvan ( 1961 )) and in applied species indicative values
(i.e., the list of Sl ´ de ˇ ek ( 1973 ) or the revised list given in the latest German
standard (DIN 38410)). Whilst sensitive to all pollution, the saprobic system
is primarily an assessment of the extent of organic pollution, and as with all
early bioassessment techniques, a method to determine the quality of water
resources for potable supply.
However, many workers wanted a numerical score, rather than one of four
conditions, to enable the extent of pollution (or recovery) to be measured
more precisely. Thus, numerical indices were adopted, such as the Trent
Biotic Index (TBI; Woodiwiss 1964 ),whichgaveasiteascoreof1to10based
on the presence and diversity of a variety of indicator taxa. As the name
suggests the index was developed for assessment of the running waters of
the English Midlands, where rivers were used to both discharge industrial and
urban waste, and as a water source for domestic and industrial use. Although
the impacts of domestic and industrial pollution on these rivers were not
separable, due to combined outfall, the index was essentially based on the
sensitivity of invertebrates to the low oxygen stress associated with organic
pollution. The TBI in turn spawned a number of indices across the globe, each
adapted to their own fauna (e.g., Indice Biotique in France (Tuffery &
Verneaux 1968 ), Chutter's Biotic Index in South Africa (Chutter 1972 ),
Hilsenhoff 's Biotic Index in the USA (Hilsenhoff 1988 )), and into other regions
of the UK where the rivers are of a different character to those of the Midlands
(e.g., Chandler's Score in Scotland (Chandler 1970 )). In 1976 the Water Data
Unit of the UK Department of the Environment convened a working party
to provide a biological classification scheme to report the biological quality
of rivers across the UK. This Biological Monitoring Working Party (BMWP)
produced a scoring system that relied heavily on the perceived tolerance of
organisms to pollution (typically sewage pollution but with no ability to
discriminate between industrial and other sources) as assessed by expert
judgement, where invertebrate families were given a score from 1 to 10
(Biological Monitoring Working Party 1978 ). Initially, the total score for all
taxa present at a site was used as an unofficial raw measure of the extent of
pollution at a site, but it soon became apparent that taxon richness and
sampling effort had an influence on this value (Armitage et al. 1983 ). To rectify
this problem, the total score was replaced by the average score assigned to all
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