About the document
This report is the product of the fourth 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 in 2017–18, complementing the first three years of LTIM Project monitoring and evaluation work undertaken in 2014–15, 2015–16 and 2016–17, and previous short term monitoring and evaluation work undertaken between 2010 and 2014.
The Lower Murray River LTIM Project identified a number of key outcomes achieved due to environmental water delivery in 2017–18:
- ‘Flowing water’ habitat (greater than 0.3 metres per second) increased in area, and water levels were more variable. More flowing water benefits native plants and animals that are adapted to a riverine environment. Variable water levels generally improve river bank plant health and increase the diversity of biofilms, which is a key component of riverine food webs.
- Flows over the barrages to the Coorong were continuous throughout the year, maintaining a connection between the river and the Coorong estuary to support a functioning river system.
- Modelling estimates that Commonwealth environmental water contributed 69% of the 349,892 tonnes of salt exported from the Basin. This is the equivalent of over 12,000 semi-trailers each carrying a full load of salt (around 20 tonnes).
- In the river channel, food production and consumption, and transport of nutrients and phytoplankton all 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.
- Oxygen in the water during spring–summer was maintained at an adequate level (8−10 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.
- Microinvertebrates from upstream sources (e.g. Goulburn River/southern Basin) were transported to the Lower Murray River, which contributed to increased diversity and potentially provided a more diverse food source for larger animals (e.g. fish).
- Spawning of golden perch occurred in the Lower Murray River, however, there was no evidence of successful ‘recruitment’, i.e. survival to juvenile stage, and consequently no contribution to the broader population. The current golden perch population in the Lower Murray is dominated by six to eight year old fish (spawned in the Lower Murray and the Darling), with negligible recruitment from the last five years.
Additional ecological findings from the LTIM Project in the Lower Murray River, for which the contribution of Commonwealth environmental water was not evaluated, include:
- Juvenile Murray cod were detected in four consecutive years (i.e. 2015 to 2018). While the reasons for improved recruitment are unclear, this is a promising sign of increasing population health of Murray cod in the Lower Murray River.
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. For example, useful ‘rules of thumb’ will inform how best to target water delivery to create flowing habitat for native fish in the Murray River.
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.