About the document
This report is the product of the fifth and final year of monitoring and evaluation in the Lower Murray River under the Commonwealth Environmental Water Office’s Long Term Intervention Monitoring (LTIM) Project. The report evaluates the contribution of Commonwealth environmental water to environmental outcomes in the region over the five years of monitoring (2014-15 to 2018-19), complementing the first four years of LTIM Project monitoring and evaluation work undertaken in 2014–15, 2015–16, 2016–17 and 2017-18, and previous short term monitoring and evaluation work undertaken between 2010 and 2014. The new CEWO Monitoring, Evaluation and Research (MER) Program, initiated in 2019-20 will extend and enhance these monitoring and research activities.
The Lower Murray River LTIM Project identified a number of key outcomes achieved due to environmental water delivery over the five years:
- The length of river with ‘flowing water’ habitat (greater than 0.3 metres per second) increased, mostly during 2017-18, and water levels were slightly more variable. More flowing water benefits native plants and animals that are adapted to a riverine environment. Variable water levels generally improve bank vegetation health and increase the diversity of biofilms, which is a key component of riverine food webs.
- The likelihood of low oxygen levels (e.g. <5 milligrams per litre, mg/L) during spring–summer was reduced due to increased water mixing and oxygen exchange from environmental water delivery. Aquatic animals generally need oxygen levels above 5 mg/L, particularly during spring–summer, which is the main reproductive season of many species.
- In the river channel, food production and consumption, and transport of nutrients and phytoplankton marginally increased. Greater primary production provides more food to aquatic food webs (e.g. for invertebrates and fish). Transported food resources from the river also benefit food webs in the Lower Lakes and the Coorong.
- Flows through the barrages to the Coorong were almost continuous throughout all years, maintaining connection between the river and the Coorong estuary. Some species need this connection to move between fresh and saltwater habitats to successfully reproduce. Environmental water substantially increased salt export out of the Basin, reduced salt import into the Coorong and reduced salinity concentrations in the Coorong. This was crucial in maintaining estuarine habitats, species diversity and ecosystem functions.
- Increased flows transported microinvertebrates from upstream sources to the LMR, and led to an increase in bank (littoral) organisms. Increased amount (density) and variety (diversity) of microinvertebrates may improve community resilience and better support larger organisms (e.g. larval fish) in the aquatic food web.
- Spawning of golden perch occurred in the LMR, but there was negligible ‘recruitment’ and diminished population resilience.
The outcomes of the LTIM Project highlight key areas for maintaining and improving Commonwealth environmental water delivery and inform adaptive management of how water is delivered for best environmental effect.
Water delivery in South Australia is connected and coordinated. Environmental water delivered to the Lower Murray provides benefits for the river channel as well as low-lying floodplain, particularly areas that are inundated by weir pool raising events. This is complemented by wetland watering via a range of partners including non-government organisations, irrigation trusts and at the internationally-important Banrock Station wetlands. As the environmental water moves downstream, it is providing benefit to the Lower Lakes and Coorong.
The environmental outcomes detected by the LTIM Project complement the results of other monitoring projects, such as those focused on wetlands and monitoring at the Coorong, Lower Lakes and Murray Mouth through The Living Murray program.
Two versions of the report are provided:
- A non-technical summary report; and
- A technical report including detailed scientific methods, analyses and results for each indicator.
The data and evaluation report from this project are being combined with those from six other LTIM Project Selected Areas within the Basin, as part of a Basin-scale evaluation of the contribution of Commonwealth environmental water to the environmental objectives of the Basin Plan being led by the Centre for Freshwater Ecosystems.
In addition to assisting the Office to demonstrate environmental outcomes, the LTIM Project is designed to allow adaptive management of the water holdings. As such, identified outcomes and limitations are used to inform environmental watering in future years leveraging the best available, contemporary scientific knowledge.