An introduction to the collection ‘Environmental flows in northern Murray–Darling Basin: what we know about the science and management after a decade of practice’

Introduction

The diverse river systems of the northern Murray–Darling Basin (northern MDB) include vast regions of semi-arid ephemeral systems and more perennial but still highly variable rivers. The water resources of the northern MDB have been increasingly captured and extracted for irrigation development since the 1970s (Thoms and Sheldon 2000), with mounting impacts on riverine ecosystems including internationally notorious fish deaths (Vertessy et al. 2019; Jose and Claughton 2023; Office of the NSW Chief Scientist & Engineer 2023). Management of the northern MDB for sustainable use that balances natural and agricultural production requires understanding of the diverse and immense riverine and wetland landscape.

The northern Murray–Darling Basin, Australia

The northern MDB includes nine major catchments. The Macquarie–Castlereagh, Namoi, Gwydir, Border Rivers and Condamine–Balonne drain the western slopes of the Great Dividing Range. The Barwon–Darling, Moonie, Warrego and Paroo drain lower-lying semi-arid landscapes in the north-westerly regions of the northern MDB. European agricultural practice has significantly affected the northern MDB, including widespread clearing of native vegetation and reductions to river flows through abstraction for irrigated crops (Bowen and Simpson 2010). Floodplain development associated with irrigated agriculture in the form of levees has also cut off vast areas of floodplain from their river channels, reducing the exchange of material during periods of floodplain inundation (Thoms 2003). These impacts have led to the overall degradation of the ecology and environments of the northern MDB (Kingsford 2000; Sheldon 2019).

In recognition of the failing environmental health of the Murray–Darling Basin, the Murray–Darling Basin Plan (Basin Plan) was developed to improve the balance of water use between the environment and agricultural production. The Basin Plan came into effect in 2012 and included voluntary water buyback as the primary mechanism to recover water for the environment. The water acquired by the Commonwealth Government as part of the Basin Plan is managed by the Commonwealth Environmental Water Holder (CEWH) (Banks and Docker 2014). This water is used in combination with State-owned or managed water for the environment to achieve environmental protection and restoration. To assist in the delivery and adaptive management of water for the environment, the CEWH and the State Governments of the northern MDB have invested significantly in monitoring and research.

The collection

The purpose of this collection is to showcase some of this monitoring and research in the northern MDB with the intent that it will also inform water-resource management in other catchments in Australia and around the world. The 12 papers feature a broad range of themes, including studies of colonial waterbirds, freshwater turtles and fish, frogs, platypuses, wetland vegetation and trophic dynamics, as well as water management.

Seven papers in this collection explore the ecology and conservation of aquatic fauna. Brandis et al. (2024) identify habitat preferences of breeding waterbirds at a Basin- and sub-Basin scale. Deppe et al. (2024) study the movement and survival responses of three species of freshwater turtle in the Gwydir Wetlands during drought conditions. Harding et al. (2024) monitor and describe flow-related movement patterns of Murray cod (Maccullochella peelii) and golden perch (Macquaria ambigua) in the Condamine–Balonne River and Butler et al. (2024) examine the residency of golden perch in the Gwydir River system. Harding et al. (2024) and Butler et al. (2024) highlight the impact of longitudinal barriers such as weirs and dams on flow-dependent large-bodied native fish. Ebner et al. (2024) detail approaches and pitfalls of housing river blackfish (Gadopsis marmorata), mountain galaxias (Galaxias olidus) and Lamington spiny crayfish (Euastacus sulcatus) after rescue from the headwaters of the Condamine–Balonne during an extreme drought. Ocock et al. (2024) investigate reproductive activity and recruitment success in flow-dependent frog species in the Gwydir Wetlands and Macquarie Marshes. Finally, Khurana et al. (2024) study the impact of river regulation on platypus population distribution and condition in the Border Rivers, Gwydir and Namoi–Peel catchments.

Three papers examine the ecology of wetland vegetation. Mackay et al. (2024) study the effects of fire and inundation on water-couch marshland in the Gwydir Wetlands. Kerr et al. (2024) assess correlations between the phenology of river red gum (Eucalyptus camaldulensis) and coolibah (Eucalyptus coolabah) and meteorological and hydrological events in the Condamine–Balonne River system, and explore comparisons with the southern Murray–Darling Basin. Last, Johnston-Bates et al. (2024) discuss projections of wetland vegetation transformation under climate-change scenarios and the implications for wetland policy and management.

Frost et al. (2024) study the foodweb mechanics of ecological response to inundation in the Gwydir Wetlands. In particular, Frost et al. (2024) explore the relationships between hydroperiod, the complexity of food-web structure and the provision of resources to aquatic-dependent taxa, such as amphibians, reptiles and waterbirds. These authors highlight the importance of preserving the wetting–drying dynamic that underpins wetland ecosystems that serve as hotspots of ecological productivity.

These papers contain valuable insights into wetland ecology but also demonstrate a critical challenge faced by water managers. Flow regimes altered by river regulation and extraction, compounded by climate change, are placing immense pressure on freshwater ecosystems. For instance, Butler et al. (2024) note that the scale of barriers and modification within the Gwydir River system may render the continued existence of a self-sustaining population of golden perch unfeasible without stocking. Similarly, Khurana et al. (2024) warn about the dangers of regulation for platypus populations. Environmental water deliveries are frequently prescribed to relieve pressure on wetland taxa; however, as Ocock et al. (2024) point out, wetland taxa often have different hydrological needs. Addressing this challenge and achieving positive outcomes for the environment relies on robust and well-informed adaptive management.

The 12th paper of the collection, McLoughlin et al. (2024), explores approaches to adaptive natural resource management, utilising the Macquarie Marshes as a case study, and stresses the importance of learning in achieving effective and successful outcomes. The learning process outlined, termed ‘requisite learning’, extends from iteratively modifying and improving policies, approaches and actions in the short and mid-term to transforming the paradigms underpinning water governance in the long term. Johnston-Bates et al. (2024) provide an example of a learning that may reflect the future of adaptive water management in the northern MDB. Namely, that wetland managers may need to abandon hope of reversing or halting changes caused by anthropogenic land use and climate change, and instead prioritise the protection of key values and functions (Johnston-Bates et al. 2024).

Conclusion

This collection has the goal of guiding the management and delivery of water for the environment in the northern MDB. In this effort, it represents an ever-widening, multi-disciplinary knowledge base that demonstrates the results that can be achieved by adaptively managing water for the environment. We encourage the readers of this collection to continue their exploration of research on the northern MDB and to consider its significance in the context of environmental water management.