Environmental Engineering Reference
In-Depth Information
aquatic ecosystems have been developed in different countries and described in literature
(Novotny 2003, Uys et.al. 1996, Hellawell 1986). In the region the South African Scoring
System (SASS) has found an application. It provides a rapid assessment of bentic macro
invertebrates using a scoring system for African families to calculate an index of
pollution, based on the number of family representatives (taxonomic groups), which are
classified depending on their tolerance to pollution. It is a rapid assessment method.
According to SASS4 the invertebrates are collected from all the principal river biotopes
at a particular site. They are taken back to a laboratory/office, removed from the debris of
the sample and identified down to family level. The samples are counted and recorded in
their respective taxonomic groups. Each taxonomic group has a grade or ranking which is
relative to its sensitivity to pollution. Families with a ranking of 1 are very pollution-
tolerant while those with a rank of 15 are very sensitive. These grades/ ranks are summed
to give the Sample Score, which is divided by the number of families of invertebrates
identified, to give the Average Score Per Taxon (ASPT). This gives the indices of water
quality when taken in conjunction with other factors such as the Sample Score. The
ASPT values usually range between 2 and 8. In general, the higher the ASPT value, the
better the water quality. The amount by which this average sensitivity deviates from the
number obtained from pristine reference sites forms the basis for a quantitative
assessment of the ecological impairment of the area. The analysis to a family level does
not require anything more than good taxonomic keys and some assistance from an
experienced person in the field.
As with any system of assessment and evaluation, biomonitoring methods and
techniques have advantages and disadvantages that need to be taken into consideration in
order to decide on the suitability of the method chosen. A brief listing is presented below:
• Advantages
Selected methods, as biotic indices, are simple to perform.
No special equipment or facilities are needed.
Biological communities may be affected by human interference in ways that are not
detected inchemical tests such as the removal of riparian vegetation, dredging and
canalization (Chessman 1995).
Both point source and non-point source problem areas may be identified.
Collecting equipment is simple, inexpensive and lightweight making it easy to
transport thus testing the maximum number of sites with the minimum amount of
effort and expense.
Rapid-assessment predictive models are simple and based on sound ecological
principles, which maybe presented in a way, which can be interpreted by non-
specialists, such as water board managers and the public. It gives a quantitative
measure of ecological impairment.
It is easy to tailor this type of model to any country and it produces results, which
are in themselveslegally defensible and can lead to enforceable management
options.
• Disadvantages
Their use is localized to the specific bio-geographical region and the comparison
between differentregions is risky;
