The puzzle of blue-green algae

The current blue green algae bloom affecting hundreds of kilometres of the Murray River system has scientists, including Institute researchers, and water managers searching for answers.

 

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Blue green algae bloom in the Upper Wakool River, March 7. Pic R. Watts

The massive bloom has been caused by excessive growth of chrysosporum ovalisporum, a species of naturally occurring cyanobacteria.

“This is the first time, that we know of, that this particular species has been the dominant species in an algal bloom in the Murray River system,” says Professor Robyn Watts. “As it is a species that responds to high water temperatures, in the light of climate change, is it a sign of things to come? What environmental factors have influenced this bloom?”

To better answer these questions, and understand the environmental factors that have led to and have maintained the bloom, Robyn and the team of Institute scientists are undertaking weekly sampling in addition to the current 5 year project examining ecosystem responses to Commonwealth watering in the Edward-Wakool River System.

“The Commonwealth Environment Water Office (CEWO) has seen the opportunity to learn from this event,” says Robyn. “The information we are getting will increase knowledge about this species of cyanobacteria and inform decisions about water delivery in the future”.

As well as being useful for future water management decisions, the information the team is collecting is also contributing to the day-to-day decisions currently being made by water managers.

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Red Scum from the blue green algae bloom. Upper Wakool River, March 14. Pic R. Watts

The information has been shared with the Murray Regional Algal Coordinating Committee, the Murray Dissolved Oxygen Group (of which Robyn is a member), Murray Irrigation Limited, the Murray Darling Basin Authority and other agencies involved in water delivery.

The bloom was first reported upstream of the Edward-Wakool River System in late January/early February around Lake Hume and Lake Mulwala with Red Alerts issued by the Murray Regional Algal Coordinating Committee in mid-February. The researchers began their weekly monitoring on March 1 and will continue until the bloom subsides. The blue-green algae first appeared in the upper part of the system and within a few weeks it was throughout the whole system.

“We have data loggers that are in the water that continuously record water temperature and dissolved oxygen concentrations and we increased sampling for nutrients and carbon from monthly to weekly sampling at 14 sites in Yallakool and Colligen Creeks, and the Niemur and Wakool River,” explains Robyn. “We will examine the relationships between temperature, nutrients, carbon, chlorophyll and blue-green algae counts. Team member Dr Julia Howitt, an environmental chemist, is analysing the effect of the bloom on the carbon signature of the water.

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Water samples of blue green algae. Pic R.Watts

“This is the first time this kind of study has been done in the Edward-Wakool River system.”

Blue-green algae (cyanobacteria) can produce toxins that affect the liver, nerves and skin.

“There is limited information on this species of cyanobacteria” says Robyn. “It is not known what temperatures this species will start to break up at; what is linked to its onset; its breakdown …they are the kind of questions we are looking for answers to.

“One of the concerns (other than the risks to human and stock health) is what will happen to the river ecosystem when the bloom breaks up. If the bloom were to break up very quickly there is the potential for a rapid reduction in dissolved oxygen which could lead to fish and other organism deaths. The bloom has impacted on the oxygen levels in the system but we haven’t seen any fish kills at this stage.
“The warm weather we had earlier in the year facilitated its growth. The water temperature at some sites in the Edward-Wakool system was very high, between 28 and 30 °C, in early March.”

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PhD Student Xioying (Sha Sha) Lui in the mid-Wakool River testing water quality. Pic R. Watts

Robyn and her team are producing weekly updates for CEWO and Robyn made a presentation to the Wakool River Association on March 14.

“The Edward-Wakool River System is a fantastic natural laboratory where we can answer a range of questions about ecosystem responses to flows,” says Robyn.

“The system has multiple rivers running parallel to each other but have the same source water (from Stevens Weir on the Edward River) but different discharges, so we are able to get a better understanding of how flow and other parameters influence the development and break-up of the bloom. It makes for very interesting science.”

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