An evaluation of SASS (South African scoring system) as a tool for the rapid bioassessment of water quality

The South African Scoring System (SASS) is a rapid bioassessment technique based on one component of riverine biotas, the benthic macroinvertebrates. Each taxon is assigned a tolerance/sensitivity score, which are summed to provide a Total Score. The Average Score per Taxon (ASPT) is calculated by dividing this Total Score by the number of taxa. This study was undertaken to evaluate the SASS technique as a tool for the assessment of water quality. Three study-sites, which differed in water quality, in the south-western Cape were selected for a detailed investigation into sample variability and replication of two methods of biological assessment, namely quantitative box-sampling and SASS. The ability of each method to differentiate between these sites was determined. The more general application of SASS in the south-western Cape was examined at forty nine sites and potential problems associated with SASS, namely biotope availability, temporal variability and longitudinal changes were investigated. A minimum of twelve and four quantitative samples is needed to ensure collection of 95% or 75% of benthic macroinvertebrate taxa respectively. Sampling within a single biotope component, such as a "riffle" or "run" would reduce the number of samples needed. A minimum of four and two SASS samples is needed to ensure collection of 95% or 75% of the taxa respectively. This technique is however designed such that only one sample is taken per site. The Total Score that one sample would produce as a percentage of the Total Score from 20 samples, were 28% , 59% and 45% for Sites 1, 2 and 3 respectively. Total Score increases with increasing sampling effort, whilst ASPT is relatively unaffected by sampling effort. ASPT should therefore be used in interpretation of scores. Variability, as determined by both quantitative sampling and rapid bioassessment, was greatest at the least impacted site. Such sites should be more intensively sampled, either by increasing the number of box- samples taken, or by increasing the time period for SASS sampling.

Grantor dc:publisher.institution

Department of Biological Sciences

Year dc:date.issued

1995

Author dc:creator

• Dallas, Helen Fiona

Advisor dc:contributor.advisor

• Day, Jenny

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/11427/21180

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/21180