Land and Water Link

Issue No. 11, December 2001

A collaborative study of the Gippsland Lakes conducted by CSIRO has enhanced our understanding of the changes affecting this unique aquatic ecosystem. According to aquatic scientist Dr Ian Webster from CSIRO Land and Water, 'The findings have demonstrated that continuing efforts to improve catchment management and reduce nutrients are critical to the long-term health of the Lakes'.

Located around 200km east of Melbourne, the Lakes comprise a vast network of coastal lagoons fed by a catchment area that stretches over large parts of central and east Gippsland, incorporating six major contributing rivers.

In the wake of European settlement in the 1840s, the Lakes' catchment areas have been modified by the clearing of lowland and foothill forests, draining of wetlands, and diversion of water from the rivers for urban, agricultural and industrial use. These changes have increased the delivery of nutrients and sediments to the Lakes and have altered the regime of freshwater inflow.

Catchment modifications, together with the creation of a permanently open Entrance to Bass Strait in 1889, have resulted in an aquatic environment that is substantially altered from its condition two centuries ago.

These changes appear to have caused degradation of the water quality throughout the Lakes. Recurring blooms of toxic blue-green algae (called Nodularia) have prompted widespread concern. The Lakes are also prone to extended periods of reduction in the oxygen content of the water on the bottom of the lakes (bottom water hypoxia). This condition occurs when bacteria consume detritus from algal blooms.

Not only have these water quality problems caused economic loss and threatened tourism opportunities, they have also had effects on the health of the ecosystem. Fish kills have occurred within the Lakes from time to time and impacts on bird life and other estuarine inhabitants are likely.

For environmental managers wanting to take action to improve water quality, the challenge has been to understand the workings of this complex ecosystem. Responding to this challenge, the Gippsland Coastal Board commissioned an environmental study to investigate the interactions between the mingling fresh and marine waters of the Lakes, and of the nutrients, sediments and organic matter that make up the Lakes environment.

This joint CSIRO and University of Melbourne project was funded by the Victorian Department of Natural Resources and Environment and a range of other stakeholders in the region, including private companies. The array of scientific expertise contributing to the study includes inputs from CSIRO Land and Water, CSIRO Marine Research, Monash University and Victoria's Marine and Freshwater Resources Institute.

In trying to understand the processes at play in the Lakes, Dr Webster's team employed state-of-the-art modelling technology to simulate influences affecting water quality and algal growth. Two different models of the Lakes systems were constructed: a hydrodynamic model to simulate the flow and exchange of marine water and freshwater; and a biogeochemical model to simulate nutrient cycling, water quality, and algal growth.

Dr Webster explains 'We looked at the likely impacts of hypothetical changes to river discharge, nutrient loads and exchanges between the Lakes and the sea. We then simulated the response to these scenarios using previously gathered data on river flows, nutrient loads, and weather.

'It should be understood that the models are an aid to understanding system behaviour, so that we can assess the effects of different options for ameliorating problems' adds Dr Webster.

The Gippsland Lakes Environmental Report, released by the Gippsland Coastal Board in November 2001, has confirmed that problems such as algal blooms are primarily related to changes in the amount and timing of nutrient additions to the Lakes.

'One of the important outcomes of the project', says Dr Webster, 'is that for the first time we can estimate the scope of the nutrient reduction required if we are to manage water quality and algal blooms. Also, we are able to assess the relative benefits of altering river discharge and the construction of a second entrance for improving the water quality of the Lakes.'

The study has important implications for managing the Lakes. It means that continuing to improve catchment management activities on land is the key to better managing nutrient inputs to this unique estuarine environment.

For further information:

Refer to the report available via the Gippsland Coastal Board website Or contact

Dr Ian Webster
Ph: (02) 6246 5581
Ian.Webster@csiro.au