Inland Waters Theme Report
Australia State of the Environment Report 2001 (Theme Report)
Prepared by: Jonas Ball, Sinclair Knight Merz Pty Limited, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06750 7
Aquatic ecosystems
This section reports on the following environmental indicators, which are defined in Fairweather and Napier (1998):
| Environmental Indicator | |
|---|---|
| IW 4.3 | River flow regimes |
| IW 4.6 | Alienated floodplains |
| IW 4.11 | River structures |
| IW 4.12 | River discontinuity |
| IW 5.1 | Vegetated streamlength |
| IW 6.1 | AusRivAS survey ratings |
| IW 6.2 | Frogwatch records |
| IW 6.3 | Fish kill records |
| IW 6.4 | Waterbirds |
| IW 6.5 | Habitat loss |
| IW 6.6 | Exotic pest flora and fauna |
| IW 6.7 | Wetland extent |
| IW 6.8 | Pest control |
Ecosystems are communities of different organisms (plants, animals and microbes) that are interdependent on each other and their physical and chemical environment. Some typical inland aquatic ecosystems are riparian, floodplain, wetland, lacustrine (lake) and groundwater systems. The aquatic ecosystems of many of our inland waters are in poor condition or have been reduced in extent due to the cumulative pressures from the development of water resources for human use and activities in the catchments. The protection and maintenance of the health of aquatic ecosystems is important because:
- they support many unique plants, animals and habitats. For example, the wetlands of south-west Australia support flora and fauna species that are found nowhere else in Australia (see the Biodiversity Theme Report). Waterbirds, fish, amphibians, freshwater crayfish and platypus all require functioning and healthy ecosystems. A decrease in the extent and/or health of aquatic ecosystems can reduce the distribution and population of many dependent flora and fauna species, causing a loss of biodiversity.
- the biological, chemical and physical functions of aquatic ecosystems are essential for maintaining 'good' water quality. Poor water quality can cause additional impacts on aquatic ecosystems and reduce the amenity of the water resources for human uses.
Ecosystem health is a concept used to describe the condition and functional ability of an ecosystem. The National Land and Water Resources Audit has defined 'health' as a measure of the overall status and likely changes in the condition of different components of an ecosystem (NLWRA 2000). Because ecosystems are the result of complex interactions between plants, animals and the physical and chemical characteristics of the environment, and they vary in type (e.g. floodplain wetlands and mountain streams) and with climatic conditions, it is difficult to select appropriate and reliable indicators of health and the appropriate scale at which to measure and interpret the results about 'health' accurately (Boulton & Brock 1999). Moreover, ecosystem health can be measured differently depending on the focus and particular goal for system management (i.e. for human uses or the protection of ecological values).
The AusRivAS assessment protocol aims to overcome some of the difficulties in assessing ecosystem health by comparing the macroinvertebrate community at a subject site with the macroinvertebrate community that is found at an undisturbed site (or reference site). Macroinvertebrates are a good indicator of ecosystem health as they are found in all aquatic ecosystems, are important in the overall functioning of ecosystems, are a food source for fish, frogs, waterbirds and platypus and can be relatively easily measured. A national assessment of the health of inland aquatic ecosystems using the AusRivAS protocol has recently been completed and the results of this assessment are presented under River health as measured by AusRivAS. Other important indicators of aquatic ecosystem health are geomorphology, diatoms, benthic community metabolism, riparian vegetation, the condition and distribution of fish, frog, waterbirds, platypus and freshwater crayfish populations.
A roadside remnant with Giant blue waterlily (Nymphaea gigantea, foreground) and Lepironia articulata (midground) in a coastal creek near Grafton, NSW, that has, as yet, not been highly modified. Both species are more common in Queensland, but reach their southern limit in northern NSW.
Source: J Bruhl (The University of New England).
Habitat condition and extent, and any changing trends in these two measures are also key indicators of ecosystem health. In inland aquatic ecosystems, important habitats include wetlands, riparian vegetation, instream vegetation and groundwater fed ecosystems (e.g. mound springs).
In order to develop management responses to protect, maintain and improve the health of inland aquatic ecosystems, realistic goals for management based on an appropriate and achievable level of ecosystem health need to be established. Some inland aquatic ecosystems have been irrevocably altered from the 'natural' state (i.e. prior to European settlement) and attempts to return these ecosystems to a 'natural' state would be difficult and expensive, and would most likely fail. A lower level of ecosystem health would be acceptable for these ecosystems compared with a pristine aquatic ecosystem in a national park, for example. Therefore it is necessary to determine realistic (and desirable) objectives for inland aquatic ecosystem management that are based on an acceptable level of health, both from a human use and an ecological perspective.