Communities caring for catchments
Module 3 - biological parameters
Waterwatch Australia Steering Committee
Australian Government Department of the Environment and Heritage, 2004
ISBN 0 6425 4856 0
This section provides a brief overview of using, calculating and interpreting your SIGNAL 2 scores. This section has been sourced from SIGNAL 2 Manual, Bruce Chessman (2003). For the complete manual list of SIGNAL scores visit www.deh.gov.au/water/rivers/nrhp/signal/index.html
The original version of SIGNAL required all macro-invertebrates to be identified to the taxonomic (classification) level of family. This is the level most agency biologists routinely used. Although species-level identification provides more information, especially on conservation values, it is a specialised and laborious task. Community groups, such as those in the national Waterwatch program, often cannot take identification to family level due to lack of access to the necessary equipment or resources. Typically, these groups identify to the taxonomic levels of order, class and phylum, depending on the type of macro-invertebrate.
SIGNAL 2 has versions to suit both family and order-classphylum identification.
Templates for result sheets for both levels of SIGNAL 2 can be found in Appendix 1 of this module.
Once you have identified all the specimens, to either the family or the order–class–phylum level, you can calculate the SIGNAL 2 score.
Each type of macro-invertebrate has a ‘grade number’ between 1 and 10. A low grade number means the macro-invertebrate is tolerant of a range of environmental conditions, including common forms of water pollution. A high number means the macro-invertebrate is sensitive to most forms of pollution. The higher the number, the greater the average sensitivity.
Generally, you should not mix grades for the family and order–class–phylum levels of identification in the same calculation. However, in family-level studies, a few groups that are more difficult to take to family level are often left at order–class–phylum level, for example, mites (Acarina) and segmented worms (Oligochaeta). In these cases, you can use the order–class–phylum grades in the family-level calculation. However, you must do this consistently if valid comparisons are to be made between SIGNAL 2 scores for different samples.
You can calculate SIGNAL 2 scores with or without abundance weighting. If no weighting is used, the SIGNAL score is the average of the grade numbers for those macro-invertebrate types collected.
If you want to use abundance weighting, you should derive a weight factor for each type of macro-invertebrate.
Various weighting schemes exist. Speak to your local Waterwatch coordinator on advice about how to do this or if this already exists for your State/Territory or region.
These calculations proceed by the following steps.
Table 6 provides a broad guide for interpreting the health of the site according to the SIGNAL 2 score of the site.
| SIGNAL 2 Score | Habitat quality |
|---|---|
| Greater than 6 | Healthy habitat |
| Between 5 and 6 | Mild pollution |
| Between 4 and 5 | Moderate pollution |
| Less than 4 | Severe pollution |
(Source: Gooderum J and Tsyrlin E, 2002)
For a more accurate interpretation of your results you should use the bi-plot and quadrant diagram method detailed in the SIGNAL 2 Manual. The quadrant diagram allows for variances in geographic regions to be factored into your interpretation. Your local Waterwatch coordinator can assist you in setting up the quadrant diagram and interpreting your results.
It is always important to remember that SIGNAL 2 scores and biplots are a simple, rapid assessment and not a comprehensive assessment of a stream or even of its macroinvertebrates. The biplot provides an indication of things that may be affecting the macroinvertebrates at the site, such as water and habitat quality.
Linking SIGNAL 2 assessments to other types of information will increase the weight of evidence and lead to more confident conclusions. Such information might include water quality test results, physical habitat assessments and assessments of other life forms, such as vegetation. Waterwatch manuals provide methods and guidance on how to undertake these types of assessments.
It is also important to understand what may be influencing the stream: the land use in its catchment, the human activities that may be affecting it, and the infrastructure present, such as dams, drains and wastewater discharge points. It is difficult to interpret results from a single site in isolation.
Animals that live in and around waterbodies occupy niches in or on vegetation, banks, rocks, submerged logs and the stream bottom. These are all examples of different habitats. The condition of various habitats is a good indication of the quality or health of the freshwater environment.