Page 2338 - Week 08 - Thursday, 5 August 2021
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The ACT government has just wrapped up a $94 million co-investment with the Australian government to improve water quality in the region—the ACT Healthy Waterways project. Nineteen water quality assets—rain gardens, wetlands, ponds and channel restorations—were constructed. These were designed as green infrastructure. Over 460,000 water plant seedlings were planted in 17 of the water quality assets, and these grew to cover a combined treatment area of almost nine hectares. In addition the riparian zone of the Molonglo River upstream of Lake Burley Griffin was restored to arrest channel erosion. The area around these projects was landscaped and over 160,000 herbs, shrubs and trees were planted from a plant list of local native species.
Together these 20 investments are now reducing the yearly load of pollutants in our waterways by an estimated average of 1,900 tonnes. Around 20 per cent of the pollution that was destined for Lake Tuggeranong is now being intercepted by the seven water quality assets built there. Feedback from residents about the water quality assets is very positive, with many locals appreciating the amenity and opportunities for exercise that these afford. Birdwatchers have enjoyed visits to the assets and drawn attention to some rare migratory visitors to the wetlands.
The estimated benefits of these water quality assets are based on water quality models. Healthy Waterways monitored water quality across Canberra and the performance of several existing assets to improve the accuracy of the models. Research was conducted by the University of Canberra to understand the links between pollution in stormwater and Lake Tuggeranong sediments and the occurrence of algal blooms in the lake. What we learned from this work is that more water quality improvements are needed. Stormwater coming from Canberra suburbs is more polluted than is desirable.
Research by the University of Canberra suggests that it is possible to suppress an algal bloom in the lakes via the use of Phoslock, which is a clay product developed by the CSIRO which binds phosphorus in water with sediments and reduces unwanted algal growth. Unfortunately, it was also determined that four to five times the amount of phosphorus required to sustain a bloom was still entering the lake from its catchment and this would very quickly negate the benefits of any such suppressant. Until we can manage this, there is no point in spending resources locking up the phosphorus in the lake sediments, as the algae will be amply fed by phosphorus pollution entering from the catchment.
The work also shows that it will be a major challenge for water quality assets to filter out all of this pollution before it reaches our urban lakes, where it can cause problems like blue-green algal blooms. Water quality assets are an essential tool to improve water quality, but there are challenges with relying on these alone to solve the problem. To stop these algal blooms, we also need to reduce catchment pollution at its source.
Every lake and pond is different, but these findings are relevant outside the Tuggeranong catchment, which is the catchment most intensively studied. We know, for example, that Lake Burley Griffin is on the cusp of either good or poor water quality. Last summer it tipped towards poor water quality, after improvements made over the last decade. We know we need to do more to prevent pollution from entering
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