Quick questions on Murray-Darling Basin case study: HSC Geography Ecosystems at Risk

The Basin has been extensively developed for irrigation since the 1880s. By the late 1990s, around 12,500 GL was being extracted annually, against natural runoff of around 12,400 GL to the sea. The Murray Mouth closed during the Millennium Drought; sustained by emergency dredging.

Land clearing for agriculture replaced deep-rooted native vegetation with shallow-rooted annuals. Water tables rose. Salt accumulated in surface soils. Around 2 million ha of Basin land is affected by dryland salinity, with around 70,000 ha of severely affected land lost from production.

Nutrient enrichment from fertilisers and animal waste, combined with low summer flows, produced major blue-green algal blooms (cyanobacteria). The 1991 Darling River bloom was 1,000 km long. Blooms are toxic to humans and livestock.

Major fish kills at Menindee Lakes on the Darling-Baaka in December 2018, January 2019, and February 2023. Estimated over 1 million fish killed in the 2018-19 event. Caused by combined low flows, high temperatures, and algal blooms creating low-oxygen conditions.

European carp dominate 70-90 percent of fish biomass in the Murray-Darling. Carp disturb sediment, increase turbidity, and outcompete natives. The National Carp Control Plan has investigated biocontrol (a carp-specific herpesvirus) but the release has been paused.

The Bureau of Meteorology projects 5-15 percent reduction in southern Murray-Darling rainfall by 2050 and greater inter-annual variability. The 2001-2009 Millennium Drought and the 2017-2020 drought were both consistent with this trajectory.

The largest restructure of Australian water policy in a century. Key elements: - Sustainable Diversion Limit (SDL). Total extraction capped at 10,873 GL/year, a 2,750 GL reduction on previous allocations. - Water recovery. Achieved through buybacks ($3.1 billion spent), on-farm efficiency upgrades, and infrastructure investment. - Environmental Water Holdings. Around 2,800 GL held by the Commonwealth Environmental Water Holder, deployed strategically to support environmental outcomes.

The Murray-Darling Basin Salinity and Drainage Strategy (1988, revised) and the Basin Salinity Management Strategy (2001-2015, 2030) have driven salt interception schemes that intercept around 500 t/day of salt before it reaches the Murray. Total salinity load to the Murray Mouth has been substantially reduced.

The Aboriginal Water Entitlements Program (2019) provides $40 million to acquire cultural water entitlements, recognising First Nations interests in the water cycle that European management ignored for over a century. Limited to date but growing.

Demand management (water restrictions), capital city desalination plants ($10 billion combined investment), regional pipelines, drought-relief programs for farmers.