Understanding ecosystem response to water management in the Murray-Darling Basin
SINCE European settlement in Australia, natural resource management has concentrated on enhancing economic and social values, with little consideration given to environmental values. After more than a century of exploitation of Australian natural resources, environmental degradation is now widespread across the continent. As a result, one of the most threatened resources today is water. Many hydrological systems, including lakes, rivers, wetlands and groundwater resources, have been substantially altered, and arguably, the system that has experienced the greatest impact is the Murray-Darling Basin.
Overexploitation has led to severe environmental stress with adverse impacts on indigenous communities and associated cultural values. Aboriginal people have lived in the Basin for more than 40,000 years and share a deep cultural, social, environmental, spiritual and economic connection to the lands within, often relying on Basin resources to provide water, food and shelter.
The Murray-Darling Basin covers over one million square kilometres, weaving an intricate network of thousands of creeks and wetlands with 23 major rivers. As suggested by the name, there are two connected main rivers in the Basin – the east-west flowing River Murray and north-south draining Darling River. Spanning over 15 geographical bioregions with diverse climates, the Basin supports more than 30,000 wetlands and thousands of ecosystems composed of rich, complex and dynamic biodiversity. Birds, fish and vegetation are examples of key ecological assets, with many of them native to Australia.
Understanding human impact on flow
The natural river flow regimes in the Murray-Darling system are highly variable, driven by cycles of drought and flood. Flow variability is the foundation upon which ecosystems have evolved in the Basin, with ecological adaptions to suit these extremes. Dams constructed to capture water and regulate flows to support growing populations, agriculture and other industries in the Basin, have resulted in altered flow regimes with loss of the natural fluctuations necessary to support the health of ecosystems within.
Documented attempts to manage the Murray-Darling Basin date back to the mid-1800s, with the states and territories uniting on common management strategies for the first time during the severe Federation Drought (1895-1902).
From the 1900s to the late 1970s, the focus remained primarily on developing water resources for human consumption, supporting agriculture and mining, resulting in environmental degradation. Vegetation clearing was a focus during these years, to provide land for irrigated agriculture, often supporting our returned soldiers.
Negative impacts became evident in the 1960s with increasing salinity related to vegetation removal followed by river mouth closures due to reduced flows in the 1980s and toxic algal blooms in the 90s. Over allocation of irrigation water in the Murray-Darling Basin has led to problems of unreliable supplies, low residual in-channel flows and conflicts between upstream and downstream users. Consequently, the environmental problems affecting the Basin include land degradation, soil and river water salinity, water quality problems, an increase in invasive species all culminating in biodiversity loss.
To address environmental degradation in the Basin, any proposed changes to water law and management will have social and economic repercussions.
History of river management
Approximately four million people currently rely directly or indirectly on the Basin for subsistence. The residents of the Basin and state and federal governments have long recognised the need to sustainably share Basin resources.
Over the past 100 years, there have been policies and planning to address the use and management of the Basins water resources. Though the first 70 years leaned heavily towards the interests of the human needs, the Millennium Drought (1996-2010) compounded by other stressors, exposed fractures in the management strategies with rivers and catchments showing signs of severe ecological stress.
The Murray-Darling Basin Agreement put forth in 1987, emphasised the need for a holistic approach to managing water resources. In 1998, the Australian Capital Territory became a signatory to the entire Murray-Darling Basin being managed as one river system with unified goals and collaborative management strategies. The last few decades, though contentious, has also demonstrated an urge to develop strategic frameworks for the efficient and sustainable reform of the Australian water industry.
The Council of Australian Governments (COAG) led the way with the development of the forward-looking and transformational National Water Initiative in 2004. This Initiative was hailed as one of the most comprehensive water reform agendas in the world, providing policy direction on all the major elements of water management required to move towards a sustainable and holistic managed river basin. The Water Act 2007, facilitated a $10 billion investment to address over-allocation and improve water efficiency via a basin plan, currently known as the Murray-Darling Basin Plan. The Plan aims to ensure water is shared between all users including the environment.
CSIRO has been a key scientific partner in the development and implementation of the Basin Plan. In 2006, CSIRO was requested by the Australian Government to lead the Murray-Darling Basin Sustainable Yields Project (MDBSY) engaged with over 15 different organizations to bring together an integrated assessment of the future availability of water within the Basin – factoring in scenarios for future catchment development, groundwater extraction and climate conditions to 2030.
Understanding the impact of environmental flows
While knowledge of water availability is key to managing Basin water resources, a commensurate understanding of ecosystem ecological response to flow regulation is also required to aid environmental management. To improve the health of the environment, the Basin Plan aims to recover water in order to deliver more natural and variable flows in the form of environmental flows. CSIRO plays an important role in provision of ecological expertise, providing rigorous science to underpin the implementation of the Basin Plan. Research undertaken to understand water requirements of key ecological assets, ensures environmental flows are delivered to maximise ecosystem response to support the environment and Basin biodiversity.
In this ECOS special feature, we share some key ecological research that has been undertaken in the Murray-Darling Basin. There is a focus on fish, birds and vegetation as key indicators of environmental condition as well as water quality and studies to mitigate the effects of invasive carp and willows, which lead to environmental degradation.