Lake Tuggeranong research trial

Research officer recording data in a boat on a lake

The Institute for Applied Ecology at the University of Canberra is conducting research in Lake Tuggeranong to identify in-lake treatments that could improve water quality and reduce the number of closures caused by blue-green algae.

Tuggeranong’s urban water filter

Lake Tuggeranong was created in 1987 as an attractive focal point for the new satellite town, a place for recreation, play, exercise and conservation. But it also has another critical role—to filter and clean the water flowing from Tuggeranong’s suburbs into the Murrumbidgee River.

Urban run-off is generally high in litter, organic matter, harmful nutrients and other pollutants and, after 30 years, the lake is literally overloaded. As a result, it is frequently closed to recreational use because of toxic blue-green algae outbreaks.

It is an ongoing challenge to manage Lake Tuggeranong so it can fulfil the recreational needs of the community while also protecting water quality downstream in the Murrumbidgee River. At the moment, the lake doesn’t appear to be performing either role effectively. Something has to be done.

What we know (and what we don’t)

Lake Tuggeranong is often closed for primary contact, generally because of algal blooms. In the 10 years to 2017, the lake was closed for an average of 93 days each year.

There are some gaps in our understanding of how and why blue-green algae forms in lakes. Key factors that can influence an outbreak include high nutrient levels (both phosphorus and nitrogen, but phosphorus is likely to be the most important of these), longer days and warm temperatures (which explains why lake closures generally occur in summer months), and stratification (warmer water on the top, colder water on the bottom).

Lake Tuggeranong appears to provide ideal conditions for algal blooms. Of all the factors listed above, nutrient load offers the best opportunity to change those conditions. Understanding where the nutrients come from and how they behave in the lake is the first step in determining what interventions will work best to improve water quality and reduce the frequency and severity of algal blooms.

The research project

The research is divided into two phases.

Phase 1 – Complete

Automated equipment was installed in the lake and in the streams that flow into the lake. This equipment  collected water samples to measure pollutant loads, oxygen and water temperature. Researchers also collected weekly manual samples of the water in the lake.

All these samples were analysed at the University of Canberra by the research team at the Institute for Applied Ecology.

The Lake Tuggeranong research revealed that the lake suffers from both:

  • high loading of pollutants from the catchment during both base flow and stormflow conditions; and
  • high ‘internal loading’ (nutrient cycling between lake sediments and the water column).

Lake waters are saturated with phosphorus and conditions conducive to algal blooms are present all year round. When the lake is stratified during warm, still conditions, release of nutrients from the sediment layer in the bottom of the lake are exacerbating the problem, elevating nutrient levels in the lake and making nutrients released from the sediments available to blue green algae.

These results informed the management options trialled in Phase 2.

Phase 2 – In progress

Phase 2 has involved a suite of in-lake trials of three algal management options, and further research on light as a factor in algal growth. These were conducted as set of experimental ‘bag in lake’ mesocosms.  The mesocosm trials consisted of:

  • a chemical treatment (Phoslock) that was hypothesized to bind phosphorous from the water column and limits the internal release of nutrients;
  • an addition of micro-nutrients (Diatomix) hypothesized to shift the phytoplankton community composition from cyanobacteria to diatom dominated;
  • an addition of hydrogen peroxide (H2O2) that was hypothesised to kill blue green algae; and
  • experimental shading to tease apart whether light or temperature are limiting growth of algal blooms in Lake Tuggeranong.

Research is ongoing and will continue into 2019/20.