Monitoring of refuges made by environmental water

‘Blackwater’ is a term used when high levels of organic material and tannins discolour the water making it appear black.

The blackwater can become hypoxic (low concentration of oxygen) when the material is broken down by microorganisms, reducing the concentration of oxygen in the water.

Concentrations less than 2mg/L can cause fish and other animals to die.

“River reaches from Barmah downstream to the lower Murray have recently experienced really low dissolved oxygen levels,” says Prof Watts, who leads the Edward Kolety-Wakool Flow-MER (Monitoring, Evaluation and Research) program funded by the Commonwealth Environmental Water Office.

In an effort to save some of the fish in the Edward Kolety-Wakool River system, CEWO, in collaboration with the NSW DPE Environment and Heritage Group, Murray Irrigation Limited, and the Edward/Kolety-Wakool Environmental Water Reference Group, have been delivering small amounts of environmental water through MIL irrigation escapes.

It is being delivered to the Wakool, Edward Kolety and Niemur rivers and Thule, Murrain-Yarrein and Cockrans-Jimaringal creeks to provide small areas (or patches) for native fish and other aquatic species so they can take refuge from the declining water quality.

“Environmental water delivered from the escapes commenced in October 2022, before the flood peaks came through,” Prof Watts said.

“CEWO wanted to start early to create the refuges and attract fish into them before the oxygen levels in the water in the rivers crashed.

“Managers have learned from previous experience in the 2016 floods, that you need to start delivering water early to create successful refuges.

“The irrigation canal network has higher levels of dissolved oxygen than river sites because the water in the canal is diverted out of the Murray River at Yarrawonga, upstream of where the major carbon inputs occur.”

Because the blackwater is so widespread, environmental water cannot be used to dilute the blackwater across the whole river system.

“There is simply not enough good quality water to improve water quality everywhere in the system. So instead, the environmental water is being used to create small ‘refuges’ of better quality water.

“Fish elsewhere in the system will continue to be impacted from the hypoxic blackwater, but animals that can access the refuges will be in better condition to survive and help recover the populations after the flood event.”

As a way of being able to provide rapid feedback to water managers and emergency response committees, and to increase knowledge about the effectiveness of creating refuges using environmental water, scientists from CSU and La Trobe University - in collaboration with local citizen scientists - are monitoring water quality and fish responses to refuge flows from the Edward River Escape and Niemur Escape.

“There are a lot of benefits having local people involved in the project,” Prof Watts said.

“Local people can share their knowledge about the river system, and it is also cost-effective to employ local people to be involved in the project because they live locally so can do the monitoring regularly.

“It is also an opportunity for local people to help protect the river ecosystem during this hypoxic blackwater event.”

One of the locals involved in this project is Anthony Jones from Deniliquin, who is assisting with water quality measurements; a job he enjoys.

“There’s a lot worse jobs than being in a boat on the river all day,” he said.

“I think it is good that locals can be involved in this kind of thing.

“It gives you a better idea and understanding of what is actually happening in the rivers whether it is to do with crays, the fish or the plant life.

“But we can also share that knowledge with other community members and groups.

“It is good to know that you are out there, whether you are doing a lot or a little, it’s at least helping towards making a bit of a difference and seeing that the environmental water is helping some fish survive.”

The project team is analysing different types of data to help answer four key questions about the outcomes of delivery of environmental water from the escapes:

• How far downstream of the escape is the refuge created under different flows? CSU scientists and local citizen scientists in collaboration with the Edward-Wakool Angling Association are taking spot measurements of water quality along the river near the Edward Escape.

• What is the effect of environmental water delivery from irrigation escapes on the water quality in the river system? Additional water samples are being collected from the river upstream and downstream of escapes and analysed by CSU scientist Dr Sha sha Liu to document the levels of carbon and nutrients in the water.

• Are fish using the refuges created by the delivery of water from the irrigation escapes? Boat mounted sonar scans are being undertaken by scientists from La Trobe University and CSU to detect the presence and location of fish in the Edward Kolety River in the vicinity of escapes. LaTrobe research officer Sam Lewis said the good news is that preliminary surveys have indicated a positive response by native fish associated with environmental releases from the escape.

• How effective is satellite data for measuring water quality responses to environmental watering compared to field observations? High resolution satellite imagery is also being used to examine water quality in the Edward Kolety river upstream and downstream of the escape.

“All of these things - the imagery, the ground collection data, the fish data, around these escapes - all fit together and will give us a really good information not only for rapid feedback for managers right now but to learn for and to monitor subsequent events,” Prof Watts said.

The escape flows and monitoring will comclude this month.

The latest information on Commonwealth environmental water delivery from MIL escapes can be found at www.dcceew.gov.au/water/cewo/catchment/mid-murray/water-use.