A study of the impact of discharges from Gisborne RWP in Victoria on the health of Jacksons Creek
K Hassell, C Kellar, K Townsend, M Arora, K Berg, A May, V Pettigrove
Publication Date (Web): 13 May 2016

Current treated wastewater discharge licenses are quite prescriptive and focus on compliance of trigger values for certain water quality parameters (e.g. nutrients and suspended solids) in the receiving waterway to ensure the beneficial uses of the stream are protected. However, the impact of these discharges will vary between streams depending on their condition and other factors (pollutants and physical condition). We believe that better environmental outcomes could be achieved if the impact of licensed discharges and their regulation are considered in an integrated catchment management framework.

This study was funded by Smartwater, Western Water and The University of Melbourne, through the Carlton Connect Initiative, to assess the impact of discharges from the Gisborne Recycled Water Plant (RWP) in Victoria on aquatic ecosystems in Jacksons Creek, from the top of the catchment in Bullengarook to upstream of the Sunbury township.  

Sources of pollutants in the Upper Jacksons Creek Catchment.
Multiple stressors were found to be contributing to biotic stress.

An integrated catchment approach, incorporating an extensive literature review of the catchment, as well as multiple laboratory and field tests, were used to identify areas within the Upper Jacksons Creek Catchment that were polluted, and to determine likely causes of biotic stress in the species tested. A weight-of-evidence approach was then used to identify the main stressors and their sources within the catchment and impacts on stream values, and we were then able to explore what specific impact discharges from the RWP were having on the health of Jacksons Creek. Considerable urban growth is projected for the catchment and, therefore, a hydrological model was developed to help test future scenarios for the catchment and the RWP.

Nutrients were high throughout the entire catchment and regularly exceeded ANZECC trigger values both upstream and downstream of the RWP. Hydrological modelling indicated that total nutrient loads are likely to decrease in Jacksons Creek with future urbanisation, as a result of changing land use. Several heavy metals, pesticides and petroleum hydrocarbons were detected in sediments and/or water collected from different sites within the Jacksons Creek catchment, with the highest levels detected at Gisborne township. 

Toxicity and biological impairment were observed in taxa collected from, or exposed to, sediments and water from several sites throughout the catchment including Gisborne township, below the RWP and below the confluence of Riddells Creek. In contrast to nutrient loads, future urbanisation is expected to increase metal and pesticide pollution, and associated with that, toxicity and biological impairment are also likely to increase in Jacksons Creek downstream of the urban growth areas (Gisborne and Riddells Creek townships). While several pollutants were detected in the RWP discharge and some toxicity and biological impairment was observed, the RWP discharge also provided beneficial flow to Jacksons Creek.

This study has provided a catchment context of how the RWP impacts Jacksons Creek. While the RWP discharges contribute nutrients and other pollutants to the waterway, the key issues impacting Jacksons Creek are the lack of environmental flows during droughts, heavy metal and pesticide pollution from Gisborne and Riddells Creek townships, and the degraded riparian habitats along most reaches. Nutrients were elevated throughout the catchment and reducing nutrient concentrations from the RWP would have no substantial benefit to downstream aquatic ecosystems. Maintaining flows, addressing urban pollution and improving riparian habitat will improve the ecological health of Jacksons Creek.

Note: This paper was presented at Ozwater’16, 10–12 May in Melbourne.

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