Maintaining water quality

Protecting water quality is fundamental to both river health and human health. It sustains riverine ecological processes that support native animals and plants and health of the wetlands. Maintaining water quality is also vital for farming, industries, human consumption and recreation as well as for our cultural and spiritual needs.

Basin governments and the MDBA have a long history of working together to manage water quality and salinity issues. This includes managing flows to reduce salinity levels and operating salt interception schemes that divert saline groundwater away from the river.

The Basin Plan builds on this work by setting targets and objectives to protect water quality for people and livestock, as well as for the Basin's rivers, wetlands and floodplains. The Basin Plan also requires water managers to consider water quality targets when making decisions about environmental watering and running the river.

Salinity management

Salinity management is one of the most significant challenges facing the Murray–Darling Basin and water users. While salt occurs naturally in the Basin's landscape, activities such as irrigation development and land clearing can cause it to concentrate in certain parts of the landscape. If it is not managed properly salt can reduce crop yields and impact on the Basin's waterways and aquatic life. High salinity levels were observed in the lower Murray during the 1960s, 1970s and through until the mid-1990s. High salinity levels meant that water was considered to be of marginal quality for farming and for drinking at Morgan in South Australia. In response governments developed long-term strategies, which included adopting a target of keeping salinity below 800 EC for 95% of the time at Morgan.

To continue to manage salinity in the Basin for the next 15 years, a new strategy, Basin Salinity Management 2030, was developed and approved by the Ministerial Council in November 2015. The strategy builds on earlier strategies and complements the objectives of the Basin Plan by supporting the obligations related to salinity targets for flow management. As shown in Figure 8, strategic actions by governments on salinity have contributed to greatly improved outcomes over time.

The Basin Plan includes a salt export objective to ensure that salt is flushed at a sufficient rate into the Southern Ocean from the River Murray system, indicatively estimated at two million tonnes per year. Due to low inflows into the River Murray system over the last three years (July 2013 – June 2016), it has not been possible to export that much salt over the barrages.

Figure 8: River Murray salinity at Morgan and impact of management strategies

A range of factors can influence how much salt is exported each year. Extended droughts and periods of below average inflows into the River Murray System may not be adequate to flush two million tonnes of salt while maintaining salt concentration in the river at acceptable levels, however the salt export would have been less without the increased flows resulting from the Basin Plan.

During periods of low flows the prevention of salt entering the river is more important than exporting salt out to the ocean. In 2015–16, the operation of salt interception schemes helped protect the river from salinity by preventing about 525,000 tonnes of salt reaching the river and riverine landscapes.

During 2015–16, salinity levels of the River Murray upstream of Murray Bridge have been low and the long-term Basin salinity target at Morgan was achieved for the seventh year in a row. Maintaining the low river salinities has delivered economic benefits for landholders, communities and industries as well as improving the Basin environment.

The Basin Plan includes monitoring salinity levels daily at five reporting sites. Results for July 2011–June 2016, see Table 1, show that the salinity target values were achieved at four of the five sites — Murray Bridge, Morgan, Lock 6 and Milang. Over the reporting period, the salinity at the Burtundy site was above the target for 32% of days. This was due to low flows in the lower Darling River, downstream of Menindee Lakes, for the third year in a row, resulting in a peak salinity of 1,764 EC in May 2016. The lack of water available from Menindee Lakes made it difficult to manage salinity in the lower Darling River.

* EC > 800 μS/cm is marginal for drinking, EC > 1,600 μS/cm is brackish, EC > 4,800 μS/cm is saline

Blue green algal bloom and blackwater events

Tapas Biswas (MDBA) and Chris Davey (MDFRC) monitoring Darling river water quality at Burtundy, New South Wales

Between February and June 2016, blue-green algae bloomed along the River Murray. The bloom was caused by a species that had not previously been recorded in the River Murray. It first appeared in Lake Hume and then spread over 1,700 km to Lock 9 near the South Australian border. The reason for the bloom is not fully understood but higher than average temperatures are thought to have contributed.

Algal blooms often are best managed at a local level but with large scale blooms, such as during 2016, cooperative arrangements were triggered via the Murray Regional Algal Coordinating Committee.

Very little can be done to control an algal bloom once it is established extensively. Flushing the river by increasing water flows can sometimes help disperse a bloom — if the water is available. During this bloom, the River Murray was run as high as practicable with the hope of breaking up the bloom but unfortunately this strategy did not work. With the arrival of colder temperatures in June the bloom began to decline and was gone by July.

It is not possible to completely eliminate the risk of algal blooms — they are a natural event, made worse by inappropriate land management, and will happen from time to time even in a well-managed system. However, a coordinated, long-term approach to managing water quality provides the best opportunity to minimise adverse events.

The change to much wetter conditions in spring 2016 and associated floods, also brought challenges such as the emergence of blackwater. The flood waters mobilised large amounts of organic matter, such as leaves and wood, from the forest floor and floodplain. The decaying organic matter resulted in low dissolved oxygen levels in the water and blackwater.

In most cases it is not possible to dilute the blackwater. However, MDBA works closely with state agencies and environmental water holders to monitor events and identify opportunities as they arise. Opportunities include looking at whether better quality water can be delivered to affected areas to create local refuges with increased oxygen levels.

For more information about salinity and water quality management in the Basin visit www.mdba.gov.au