CSIRO offers insights into managing toxic blue-green algae

With the winter months drawing to a close, many councils and water authorities around Australia will soon start managing cyanobacteria or blue-green algal blooms in waterways and reservoirs caused by seasonal temperature increases.

As part of a series on algal blooms, Water Source discussed the leading factors contributing to toxic algal growth with leading experts from Australia’s national science agency, CSIRO and what can be done to help manage the issue.

CSIRO Land and Water Senior Principal Research Scientist Dr Grant Douglas said blooms, particularly toxic blue-green algae, can pose significant health risks to communities and the environment.

“Algal blooms are a key threat to global security. The cost of algal blooms and their effect on aquatic systems and human health is estimated to be $10 billion globally per year,” he said.

“Nitrogen and phosphorus are the key foods upon which algae grow. When there’s excess of these nutrients it can lead to the occurrence of large and sustained algal blooms. But it can also drive more toxic species of algae, such as blue-green algae, or cyanobacteria.

“This can pose a very significant problem. The water can be unfit to drink for humans, but also for livestock and wildlife. When the blooms die, during decay and collapse, they consume the oxygen in the water, which can lead to large-scale fish kills.

“There is also the issue of loss of amenity. Once a toxic algal bloom is underway, the waterways affected are usually out of bounds.”

Leading causes of cyanobacteria

Douglas said there are a few elements to consider in terms of the leading causes of algal blooms at a catchment level, including the introduction of excess nutrients to water bodies.

“One approach is managing nutrient inputs into the system. Those nutrient inputs can come from sediment, there could be runoff in the catchment that can transport nutrients into water bodies,” he said.

“This can also be caused by flood events, or land clearing that has led to large scale erosion. Inadvertent sewage inputs can be an issue as well, but also agricultural fertilisers that have not been fully utilised by crops or pasture.”

While these sources of nutrients at a catchment level can contribute to algal blooms, it’s just one part of the equation, Douglas said.

“Warm temperatures in spring and summer are one contributing factor, but also drought and climate change. When there is less rainfall, there is less flow in our waterways, which means less dilution and transport of those nutrients out of the catchment,” he said.

“Lack of flow in a river system can lead to ponding. Those ponds can get very warm. This hot, stagnant water can increase the rate of growth of algal blooms. We’ve seen it in the Murray and Darling Rivers: lots of nutrients, lack of flow, high temperatures and away you go.”

Douglas said it is important to note that algal blooms have always been around, but that human factors have led to increased occurrence and more sustained bloom events.

“They are a naturally occurring element of our waterway systems. But we’ve created conditions that have led to more frequent and sustained blooms,” he said.

Managing factors that lead to algal blooms

In terms of reducing the likelihood of occurrence of cyanobacteria, Douglas said caring for the ecosystem is the first important consideration, which can include ensuring there are sufficient environmental flows as a preventative strategy.

“By releasing sufficient water back into the system, it’s not only flushing nutrients through the system, but it’s also hugely beneficial for the rest of the ecosystem. When you have adequate flows, the water is oxygenated, too,” he said.

“Managing sediment inputs is another strategy. By establishing riparian zones on the banks of our rivers, we can intercept sediments before they reach the waterway. Establishing more targeted fertiliser use that limits offsite transport can help too.

“Prevention is always better than cure. Utilising management strategies before the bloom starts means that, if you do get a bloom, it's going to be less severe, and easier to mitigate.”

Once an algal bloom is underway, Douglas said in-situ mitigation often involves treating the waterbody with oxygenation or aeration techniques, or destratification.

“Oxygenation involves inputting a highly enriched oxygen stream into the waterbody, and aeration is inputting air as it is into the water body. This maintains oxygenated conditions, which often decreases the level of phosphorus coming out of sediments,” he said.

“Destratification, or intentional mixing of the water column, is another option. When there’s a stratified water body, there may be a zone on top with enough oxygen, and a layer below, a low oxygen zone.

“This can lead to enhanced amounts of nutrients coming out of the sediment. By artificially mixing the water column, you're improving the overall oxygen status of the water column, reducing nutrient release.”

Furthermore, Douglas developed a management strategy 25 years ago that involves applying clay, which acts as a sponge and absorbs phosphorus from the water.

“Clay is added to the water column. It absorbs the phosphorus and settles on the bottom, creating a blanket on the bottom of the water column, further intercepting nutrients that are released from the sediments,” Douglas said.

“Another strategy is to use flocculation, dragging algal cells from the surface of the water to the bottom. By physically moving those algal cells to the bottom of the river or lake, it reduces the amount of light they can access for growth.”

While these strategies have been utilised to help manage blooms for quite some time, Douglas said there’s no solution that doesn’t require careful consideration of all the varying factors that contribute to the problem.

“It’s a balancing act. You want to try and cut back as many nutrients from entering the waterbody, and there will be various levels of success with that. But even if you manage nutrients, there’s still often a lot of nutrients in the bottom sediments,” he said.

“That’s where keeping an eye on oxygen conditions comes in. There isn’t a simple solution, it’s a complicated process to manage.”

Using data to manage blue-green algae

The problem is complex and, as Douglas suggested, prevention is an important focus, but water managers may soon have access to a solution known as AquaWatch Australia: a world-first water quality management aid under development with the CSIRO.

CSIRO Centre for Earth Observation Director Alex Held said that while AquaWatch Australia is currently in an inception phase, the water quality monitoring system should be set up within Australia by 2025-26.

“This system will include a dense network of ground-based water quality sensors placed in water bodies across the continent and these will be critical to informing and connecting with water quality prediction models,” he said.

“These high-resolution measurements from the in-situ sensors will be supplemented by Earth observation satellites to create a national overview and deliver critical data on the health of our inland and coastal waters.

“All the data will be integrated into a single platform and customised for water quality managers around the country, in a way that is visual and easy to understand, but also quantitative.

“Water managers will be able to look at concentrations of different things in the water that might trigger blooms, whether that’s low oxygen, high temperatures or nutrient levels.”

While the use of Australian satellites in future will be subject to funding, Held said the mission hopes to begin developing the integration of existing satellite data and work on bringing the data sets together next year.

“It’s a world-first. Our goal is to be able to predict one or two days ahead, so that water managers can act before a bloom actually occurs. It will work as an early warning system, which will be of significant help in terms of prevention,” he said.

Held said the development of the water quality management system has focused on ensuring the data is applicable and sufficient for the needs of the water sector, with the aim of creating a tool that supplements the work already being performed.

“We’ve done a lot of work in the past year with water managers from different parts of the sector in order to identify the current gaps or needs in terms of monitoring requirements. This information has been translated to a technical specification,” he said.

“In-situ sensors will measure at the location, but unless you have lots of them, in a lake or reservoir, for instance, you won’t know the spatial distribution of the algae blooms.

“The satellite imagery will provide a synoptic view of the waterbody so that managers can more easily decide where to extract healthy water. The data analytics system will create a visual representation, both coastal and inland, across the continent.

“AquaWatch is not about replacing current agency activities, we are hoping to supplement their efforts by enriching the data and making that data available to a lot more people.”