Monitoring River Health Initiative
Building a River Health Model
Stream Invertebrate Grade Number Level (SIGNAL)
Uses of the Model
The Monitoring River Health Initiative is a subprogram of the National River Health Program which provides a means of assessing the ecological condition of rivers and streams by using macroinvertebrates.
Aquatic macroinvertebrates (such as insects, snails and worms) are now well recognised as powerful tools for monitoring river health. They can - by their presence or absence - tell us a lot about the condition of our waterways.
River macroinvertebrates are sensitive to changes in habitat and water quality. Some species are known to have particular tolerances to environmental factors such as temperature or levels of dissolved oxygen. Other information can be obtained from the number of species found at a site (diversity), and the number of animals found at a site (abundance).
By sampling aquatic macroinvertebrates from relatively undisturbed rivers, researchers and community groups, such as Waterwatch, can find out the range of species that should be present in undisturbed and unpolluted river habitats.
Riffle Sample - A sample is taken from shallow, fast flowing areas with a stony or rocky substrate. This type of habitat is called a riffle. In order to collect a sample, the stream bed is disturbed by the sampler’s feet and dislodged animals are swept into a net by the current.
Edgewater Sample - A second sample is collected by sweeping the net along the edgewater or margins of the river and in backwaters and pools which have slow currents or no flow. Aquatic plants (macrophytes), which provide additional habitat for aquatic macroinvertebrates, are often found in these edgewater habitats and are included in the sweep sample.
Physical (vegetation and substrate composition) and chemical (water quality) properties are also measured. The aquatic macroinvertebrates are sorted and then taken back to the laboratory for identification.
Essentially, AUSRIVAS predicts the macroinvertebrates that should be present in specific stream habitats under reference (undisturbed) conditions. It does this by comparing a test site with a group of reference sites that are as free as possible of environmental impacts but have similar physical and chemical characteristics to those found at the test site. The AUSRIVAS models in Tasmania are based on samples taken from over 200 reference sites (see map below). In addition, over 400 test sites have been assessed using the AUSRIVAS models.
Each family of macroinvertebrates is assigned a grade according to their tolerance to pollution or disturbance. A grade of 10 represents a high sensitivity to pollution and a grade of 1 represents a high tolerance to pollution.
The “observed” SIGNAL score is the sum of the grades divided by the number of taxa collected and the “expected” score is the sum of the grades divided by the number of taxa expected.
O/E is sensitive to a wide variety of disturbances provided they result in the loss of families of macroinvertebrates from the habitats sampled at a site. Thus, this index should detect the:
Department of Environment and Heritage
National River Health Program
Monitoring River Health
Contact: River Health - Contact 1Tom Krasnicki
Senior Aquatic Ecologist (River Health)
13 St Johns Avenue
New Town TAS 7008
Phone: 03 6233 3195
Fax: 03 6233 6881
Department switchboard: 1300 368 550 (local call cost)
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