Georges River Studies Helps River Conservation

Ecosystem Guidelines for the Conservation of Aquatic Ecosystems of the Georges River Catchment: A Method Applicable to the Sydney Basin Click here for pdf of study

Abstract:
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 suitableand 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

Is Catchment Imperviousness a Keystone Factor Degrading Urban Waterways? A Case Study from a Partly Urbanised Catchment (Georges River, South-Eastern Australia

Abstract

The extent of catchment impervious surface is recognised to be an important factor associated with the condition of urban freshwater streams. We tested the hypothesis that the degree of catchment imperviousness predicted the relative ecological condition of freshwater reaches within the network of streams and rivers in the partly urbanised Georges River catchment in temperate south-eastern Australia. The 2-year study involved two spring and two autumn assessments of water quality (chemical and physical) and ecological condition, using benthic macroinvertebrates, riparian vegetation and calculation of catchment imperviousness. The study revealed that highly urbanised streams had strongly degraded water quality and macroinvertebrate communities, compared to clean non-urban reference streams. We found three clear groups of sites with varying degrees of ecological condition, being categorised according to the level of catchment effective imperviousness (low <5.0 %, moderate = 5.0–18.0 % and high >18.0 %). Water pollution also varied according to these categories. A combination of two water chemistry attributes (total nitrogen and calcium), along with catchment imperviousness and riparian vegetation condition, were identified as being the factors most strongly associated with variation of macroinvertebrate communities. Based on our results, we recommend that protection of the ecological condition of streams should focus on not only water quality but also include catchment imperviousness and riparian vegetation condition.

The influence of concrete on the geochemical qualities of urban streams

Abstract

The geochemical signature of freshwater streams can be used to determine the extent and nature of modification to stream water geochemistry due to urban development. This approach used the Gibbs (1970) diagram as a model for evaluation of changes to ionic composition linked to urban development. In this multi-year study, the geochemistry of 21 waterways in the Georges River catchment, Sydney, were monitored and compared with the level of urban development as measured by sub-catchment imperviousness and directly connected imperviousness. The results reflect a strong relationship between the intensity of sub-catchment urban development and stream geochemistry. All major geochemical attributes increased with escalating levels of urban development. The largest increase was for bicarbonate, which increased 18 times from a mean of 6.4 mg L–1 at non-urban streams to a mean of 118 mg L–1 at urban streams. Similarly, mean concentrations of calcium increased by 14 times (from 2 to 27.9 mg L–1). Mean salinity was enriched in the most urban streams, compared with non-urban streams, by more than 6 times. We attribute this, in part, to the influence of urban geology, notably concrete stormwater infrastructure. Changes in stream geochemistry due to urban development are an important element of the urban stream syndrome.

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