MER Lower Murray 2019-20 Annual Reports

About the document

The summary and technical reports present the 2019-20 results from the Commonwealth Environmental Water Office’s (CEWO) Monitoring, Evaluation and Research (MER) Project (Flow-MER) in the Lower Murray River. Monitoring and research activities in 2019-20 included the monitoring of Hydrology, Stream Metabolism and Water Quality, Fish Community, Hydraulic Regime, Matter Transport and Coorong Habitat, Littoral Vegetation Diversity and Productivity, Microinvertebrate Assemblage, Murray Cod Recruitment, Flow-cued Spawning Fish Recruitment and Lamprey Migration. Both reports evaluate the contribution that water for the environment has made to environmental outcomes in 2019-20 in the Lower Murray River, building on the monitoring and evaluation undertaken from 2014-2019.

Key findings include:

• Increased flowing habitat: The length of river with ‘flowing water’ habitat (greater than 0.3 metres per second) increased by 10% (for at least a four-week period).
• During spring–summer, increased water mixing and oxygen exchange (due to more flowing water) decreased the likelihood of low oxygen levels (e.g. <5 milligrams per litre, mg/L). Aquatic animals generally need oxygen levels above 5 mg/L, particularly during spring–summer, which is the main reproductive season of many species.
• Increased Murray cod recruitment, potentially supported by the increased extent of their favourable (flowing water) habitat during the spawning/early larval period, and increased larval food resources.
• Increased water level variability: Water for the environment, in combination with weir pool manipulations, increased water level variability. Subsequent inundation of the riverbank increased the diversity of native vegetation on the bank.
• In the river channel, food production marginally increased (by ~1%) due to changes in water level and channel width. Nevertheless, the amount (density) and variety (diversity) of microinvertebrates increased due to water for the environment, likely through inputs from off-channel or upstream environments as a result of increased lateral and longitudinal connectivity.
• Spawning of golden perch occurred in the Lower Murray, but there was negligible ‘recruitment’ and diminished golden perch population resilience. The current fish community in the Lower Murray is characteristic of low river flows.
• Maintained connectivity between the river, Coorong estuary and Southern Ocean. Flows through the barrages to the Coorong were continuous throughout the year and comprised of 100% Commonwealth environmental water.
• Barrage flows during winter and spring facilitated connectivity and promoted lamprey migration. Migration between fresh and saltwater habitats is necessary for lamprey to successfully reproduce.
• Water for the environment substantially increased salt export out of the Basin (by 623,999 tonnes), reduced salt import into the Coorong (by ~5.5 million tonnes 2017-20) and reduced salinity concentrations in the Coorong, which maintained estuarine habitats (e.g. for fish and aquatic vegetation) in the Coorong. This was crucial in maintaining species diversity and ecosystem functions.

The information from the Lower Murray MER reports is being combined with six other MER Project Selected Areas to provide a Basin-scale evaluation (led by the Commonwealth Scientific and Industrial Research Organisation (CSIRO)) of the outcomes of water for the environment. Recommendations and limitations outlined in the Flow-MER Program are used to inform future management of water for the environment, using the best available scientific knowledge.

Further information:

• Monitoring - Lower Murray-Darling