Commonwealth Environmental Water Office Long Term Intervention Monitoring Project Gwydir River System Selected Area 2017-18 Annual Evaluation Report

About the document

This report is the product of the fourth year of monitoring and evaluation in the Gwydir Valley 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 2017-187, complementing the first three years of LTIM Project monitoring and evaluation work undertaken in 2014-15, 2015-16 and 2016-17.

The Gwydir Valley Rivers LTIM Project identified a number of key environmental outcomes achieved through the use of environmental water in 2017-18, including:

River Channels

• Water for the environment contributed to connectivity in the Gwydir River, lower Gwydir River, Mehi River, Moomin Creek and Gingham watercourse during 2017-18, in what was a dry year in the system.
• Environmental water improved water quality, stimulated primary production and helped to maintain local and regional scale aquatic invertebrate diversity, and thus provide a range of food sources for other animals.
• Environmental water stimulated the movement of fish species within and between the Mehi and Gwydir River channels.

Wetlands

• Consistent with planned natural wet and drying cycles, wetland inundation within the Selected Area during 2017-18 was the lowest recorded in the four years of the LTIM project.
• Environmental water increased the level of inundation in the lower Gwydir wetlands.
• Providing flows to the wetlands has been shown to promote invertebrate production, waterbird populations and plant health.
• Inundated sites supported many threatened and migratory waterbird species in 2017-18.

Implications for Commonwealth environmental water management

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. For example:

• The findings from the 2017-18 water year suggest that the current practice of using environmental water based on natural flow cues is working in the lower Gwydir River system, and more broadly that the long-term environmental watering strategy being employed in the Gwydir river system continues to be effective for maintaining ecological communities within the Selected Area.
• Flow events delivered earlier in the water year (winter/spring) improve water quality, stimulate fish to move through the system and encourage the development of diverse invertebrate communities. Primary and secondary production during flows at this time of year are limited by colder water temperatures.
• Flows delivered over the summer/autumn period tend to improve water quality, and promote primary and secondary production, thus supporting animals further up the food chain such as fish, frogs and waterbirds.
• Providing flows to the wetlands has been shown to promote invertebrate production, waterbird populations and vegetation condition.
• The fish population in the Gwydir River system remains under stress, with many native species in low abundance. The low fish abundance may reflect the limitations on fish populations with system in its current state. While some species appear to be breeding and recruiting, others, especially iconic species such as golden perch, freshwater catfish and Murray cod, are not recruiting sufficiently to improve their populations. Along with providing environmental flows, other options such as habitat rehabilitation, restocking and barrier remediation should be considered to improve the fish communities of the Selected Area.

This report is the fourth of five to be produced for the Gwydir Valley Selected Area under the LTIM Project, with monitoring and evaluation being undertaken from 2014-15 to 2018-19. 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 Murray-Darling Freshwater Research Centre.

Further information

• Gwydir catchment - Long Term Intervention Monitoring

A live Murray cod (Maccullochella peelii) being implanted with acoustic tag to allow tracking after release

Australasian Darter (Anhinga novaehollandiae) sunning at Gingham waterhole