• Energy Research

Freshwater ecosystems, including rivers and floodplain wetlands, face severe stress from unsustainable water resources development, with climate change exerting further pressure. This study compares the relative effects of river regulation and projected climate change on river flows to the semi-arid Lowbidgee Floodplain (3250 km2), the largest wetland ecosystem on the heavily regulated Murrumbidgee River, Australia's second longest river, within the Murray-Darling Basin. We modelled annual natural streamflow in the lower Murrumbidgee River before major dam constructions and water diversions (1890-1927), linking river flows to runoff from the upper Murrumbidgee catchment. Extending this analysis to the full rainfall-runoff dataset (1890-2018), we compared modelled natural flows to observed river flows affected by dams and water withdrawals. Additionally, we modelled climate change impacts on river discharge and overbank flows, which reduced inundation of riparian habitats. Current river regulation has reduced median annual streamflow by 43% from 2565 × 106 m³ to 1490 × 106 m³ during 1958-2018, relative to modelled natural flows, with a more pronounced 55% reduction in the last three decades (1988-2018). The return period of major overbank flows, essential for river-floodplain habitat connectivity, more than doubled from once every 2.0 years to once every 4.4 years (1916-2018). Mean climate change projections indicated an additional 7-10% decrease in median annual streamflow by 2047-2075, relative to 1977-2005. The annual duration of major floods declined from an average of 11.3 days under natural flow conditions to 4.5 days under the current regulated river flow regime, with a further reduction to 1.6-1.8 days (83-85% decrease) projected by 2047-2075, due to climate change. We recommend prioritising mitigation of river regulation effects, as these pose the most immediate threats to riverine ecosystems, including their native biodiversity, in the Murrumbidgee River catchment. Our 'natural flow' model offers critical insights for shaping environmental policy and managing environmental flows to mimic natural flow regimes, supporting the conservation and restoration of freshwater ecosystems, like the Lowbidgee Floodplain wetlands. Our approach is transferable to other large river systems globally, using available or modelled streamflow data.

The Murray-Darling Basin (the Basin) is the largest river system in Australia, supplying about 40% of the country’s irrigated agricultural output. Associated water resource development has come with a heavy price for the Basin’s freshwater ecosystems degrading them over decades. Australian governments are attempting to achieve environmental sustainability by returning water to the environment through buy-back of irrigation licences and improved water efficiencies. To determine effectiveness, basin-wide management objectives were established for key indicators, including waterbird populations and life histories which can effectively indicate ecosystem function and condition, driven by flow and flooding regimes. Ongoing monitoring of waterbird numbers indicates continued declines. We evaluated the feasibility of meeting established waterbird objectives under existing and predicted climates. We modelled long-term waterbird numbers using one of the world’s largest ongoing waterbird surveys (1983–2020), covering about 13.5% of the area of the entire Basin. Our findings suggest that under near future climate change projections, waterbird numbers will likely continue to decline, and remain below restoration targets set for the Basin. We discuss the current policy settings for using environmental water to support waterbird populations, recommending adjustments to restore the Basin’s waterbird populations and their wetlands in order to meet Australia’s conservation targets in relation to the ongoing global crisis of biodiversity loss.

The Malkumba-Coongie Lakes Ramsar Site has extensive terrestrial and freshwater ecosystems (largest Ramsar Site in Oceania, 2,178,952 ha, designated in 1987), including freshwater and salt lakes, lignum swamps and river channels in central Australia. It is supplied by Cooper Creek, a free-flowing Lake Eyre Basin river system. The area includes pastoral leases (97% of site grazed, including a regional conservation reserve (35%)) and a National Park (3%), with the largest oil and gas production field in Australia. We developed a Strategic Adaptive Management (SAM) Plan, linking science, monitoring and management of this social-ecological system, involving stakeholders and workshops. This involved developing a shared vision and hierarchy of objectives linked to management actions and identified outputs and outcomes. We exemplify this approach with explicit and measurable end-points (thresholds of potential concern) culminating from low level objectives for fish communities, particularly the alien sleepy cod Oxyeleotris lineolata. We describe this framework, highlighting the benefits in prioritizing management actions and monitoring in collaboration with a diverse range of stakeholders, driving adaptive feedback for learning. The whole approach is aimed at successfully achieving mutually agreed management objectives and the vision to maintain the ecological character of the Malkumba-Coongie Lakes Ramsar Site.