River Health in the New South Wales Lower North Coast, Hunter and Central Coast Catchments
A report of AusRivAS assessments 1994 - 1999
Grant Hose and Eren Turak
Environment Protection Agency, 2004
ISBN 0 642 55099 9 ISSN 1447-1280
2. Assessing river health - more than just a water sample
Historically, water quality, as determined by physical-chemical parameters, has been used as a general surrogate for the reporting of ecological condition of aquatic ecosystems. In more recent years it has been increasingly recognised that water quality and ecological health do not necessarily go hand in hand, and achieving "clean water" is not enough for protecting aquatic ecosystems (Karr 1995).
Biological indicators provide a tool that can be used in combination with physico-chemical water quality assessments to give a more holistic indication of river health. The basic issue however is defining a healthy river. A simple definition is a healthy river is one which has a community of organisms where the species composition, diversity and functional organisation is comparable to that found in the natural habitats of the region (Schofield and Davies 1996).
In the AusRivAS assessment program, this is referred to as the 'reference condition ' and is represented by a collection of 'reference sites '. The results from the macroinvertebrate assessments undertaken at these reference sites are used to create a representative data set that forms the bases for the AusRivAS predictive models.
For the most effective monitoring and reporting of ecosystem health, all components (both physical and biological) of the river ecosystem would be used to determine river health. In reality, however, ecosystems are so complex that such an all-encompassing assessment is not possible. It is necessary, therefore to use an indicator or a set of indicators, which provide much information about the condition of the ecosystem while being inexpensive and practical to use.
Macroinvertebrate assemblages are a common choice for assessing the general health of rivers because they are abundant and widespread, easy to collect and identify, and contain a large number of species that display a wide range of sensitivities to pollutants. Because of their relative immobility, macroinvertebrate communities reflect the condition at the actual site of collection and, because of their relatively long life span, they can reflect the effects of intermittent pollution. For these reasons, assessments using macroinvertebrates often provide the greatest amount of relevant information on the condition of rivers for a given amount of monitoring effort and resources.