Charles Sturt University (CSU) research is informing strategies to reduce native fish deaths following recent flooding in southern NSW.
The researchers from CSU's Institute for Land Water and Society (ILWS) are working with the Commonwealth Environmental Water Office, other water management agencies and the community.
CSU aquatic ecologist, Professor Robyn Watts said, "Blackwater is a natural process that occurs when a large amount of carbon and nutrients are brought into the river with the floodwater. When there is a high level of biological activity, dissolved oxygen can to fall to very low levels, referred to as a hypoxic event, which can result in fish and crustacean deaths.
"Recent flooding has caused a hypoxic event in the Edward and Wakool rivers and our research is being used to inform decision making about how to mitigate the impacts."
Professor Watts leads a team of researchers who are monitoring the ecosystem responses to environmental water in this river system.
The monitoring is being funded under the Commonwealth Environmental Water Office's Long Term Intervention Monitoring project in the Edward-Wakool River system.
Team member, Dr Julia Howitt from CSU's School of Agricultural and Wine Sciences, said within the irrigation canal network in this region there are sites called escapes, where water from irrigation canals can be released into the rivers.
"Water in the Mulwala Canal system currently has less carbon and more dissolved oxygen than that in the river because the canal water comes from Lake Mulwala which is upstream of large forests that are flooded and are contributing dissolved carbon and nutrients from the soil, fallen gum leaves and other vegetation.
"The Mulwala Canal network provides an opportunity to bypass the forests and potentially deliver better water quality and provide local areas of refuge habitat for animals such as Murray cod and Murray crays."
Professor Watts said the effectiveness of this strategy was studied during a hypoxic event following a smaller flood in 2010.
"We examined dissolved oxygen and fish responses to the environmental flows from irrigation escapes, that were implemented during this hypoxic blackwater event in the southern Murray-Darling Basin, comparing responses in reaches receiving environmental flows to those not receiving environmental flows," Professor Watts said.
"The research found that the dissolved oxygen in the rivers was higher at sites downstream of irrigation escapes where the environmental flows were released into the river compared to those upstream of escapes. The number of days when the dissolved oxygen was below critical limits was reduced at sites downstream of escapes.
"Fish communities were maintained and there were no fish deaths recorded in river reaches immediately downstream of escapes, whereas in all other parts of the system the fish community was severely depleted and reports of fish deaths were extensive."
"This strategy is being used again now with Commonwealth environmental water being delivered through irrigation infrastructure into the Edward River to create refuges for fish threatened by the hypoxic water."
The ILWS water team is undertaking weekly monitoring at a range of sites throughout the river system to investigate the impact of the recent flooding and the resulting blackwater event.
"This real time information will be used to inform the adaptive management of environmental water during this event," Professor Watts said.