Ecosystem guidelines for the conservation of aquatic ecosystems of the Georges River catchment: a method applicable to the Sydney basin

For waterway managers the conservation of freshwater streams in Australia is commonly underpinned by comparing water quality data with default ANZECC water quality guidelines. However distinctive conditions found within many streams of the Sydney basin render a number of the default guidelines not suitable and prone to misinterpretation. In this study we draw on a three year monitoring program and follow the framework recommended by the ANZECC guideline to develop a catchment specific approach for the conservation of aquatic ecosystems for the Georges River catchment. In addition to the ‘common’ set of water quality guidelines we include values for a selection of ionic parameters and guideline values for aquatic macroinvertebrate communities, riparian vegetation condition and catchment imperviousness. The study revealed three distinct patterns of ecosystem disturbance and water quality characteristics that corresponded to the level of development across the catchment from reference forested areas through to highly urbanised centres. When compared to non-urban reference sites streams with greater than 5% impervious surfaces showed emergent signs of ecosystem degradation while those with >19% imperviousness had highly degraded water quality, macroinvertebrate communities and riparian vegetation. Based on the results of this study, we recommend two sets of regionally relevant ecosystem and water quality guidelines, one for the conservation of streams with high ecological value that would apply to waterways with minimally disturbed catchments and the other to apply to urban streams and stream restoration projects. Although the focus of this paper is the Georges River catchment, the approach developed in this study can be easily applied to other urban catchments within the Sydney Basin.