Engineering a crisis in a Ramsar Wetland: the Coorong, Lower Lakes and Murray Mouth, Australia

The Coorong, Lower Lakes and Murray Mouth (CLLMM) in South Australia, at the end of the Murray-Darling river system, were declared a Ramsar Wetland of International Importance in 1985. Historically, the wetland has relied on inflows from the River Murray. These began to decline after irrigated agriculture was established along the river in the late 19th Century, and seawater incursions to the CLLMM increased until construction of tidal barrages near the mouth was completed in 1939-40. Flows continued to decline with the building of dams upstream and increased diversions throughout the Murray-Darling Basin. Despite the imposition of a ‘cap’ on diversions in 1995, flows were further reduced by a decade-long drought. At least another decade of average or greater rainfall is now needed to restore the Basin’s reservoirs to full capacity. At the Murray Mouth, long-term median annual flows declined by 71%, with a 89-96% reduction in the driest 20% of years. Water levels in Lake Alexandrina and Lake Albert have fallen below sea level and the salinity of the Coorong has increased while the Murray Mouth requires continual dredging. Building weirs and other regulatory structures, pumping water to flood the exposed areas and limestoning, mulching and planting are addressing a threat from newly-exposed Acid Sulfate Soils (ASS) around the lake margins. There is a plan to pump hypersaline water from the Coorong to the ocean, to offset increasing hypersalinity in the South Lagoon caused by a lack of freshwater inflows. A last-resort option is to abandon the wetland as a freshwater environment and open the barrages to allow seawater into the lakes. Projected rises in sea level, associated with global warming, suggest that the sea could invade the region in 25-50 years; if this is correct then, there are limited prospects for long-term management of the Lakes as a freshwater system. The ecological character of the CLLMM is changing rapidly. For example, bird numbers have declined sharply, species of freshwater fish are threatened and diadromous species are denied passage between the river and ocean. Calcareous masses formed by the tubeworm Ficopotamus enigmaticus, an invasive brackish-water polychaete, have proliferated in Lake Alexandrina and killed many freshwater turtles. There are socioeconomic impacts on regional agriculture, boating, fishing and tourism. Governments are planning to spend up to $2 billion on engineering interventions, planting, other mitigation programs, community initiatives and securing water for Adelaide, as well as schemes to recover water for the environment, but progress is slow. The short-term future of the CLLMM is in the hands of the South Australian Government, and its long-term future will depend on how much water state and Commonwealth governments can recover for the environment via a Basin Plan developed by the Murray-Darling Basin Authority (MDBA) in compliance with the federal Water Act 2007. A target of an annual median flow of 3,800 GL at the barrages represents a flow that would restore low flows (below the median) when the system is most vulnerable to about one third of natural volume, considerably below historical levels, but probably allowing establishment of an estuarine-freshwater ecosystem in the Lower Lakes. This would represent an increase of about 700 GL (6%) in median annual flows at the barrages to be managed through flow rules. The unsustainable state of the CLLMM fails to meet a key objective of the National Water Initiative, signed by most governments in 2004 to return overallocated systems to environmentally-sustainable levels of extraction. We endorse some government initiatives, but have reservations about the long-term consequences of engineering works and contend that fragmentation of the regional environment to expedite management is not consistent with ecological science or wise natural resource management in the long term. We also acknowledge that the quantities of water required to secure the CLLMM are considerable, particularly given the competing demands from human consumers and other parts of the environment. There is a perception that there is insufficient water in the system and that the CLLMM will be deprived of flows as global climate change progresses and eventually be inundated by rising sea levels. These risks exist but with careful management of water resources and a level of sophistication not yet approached in the management history of the Murray-Darling Basin, the CLLMM can be saved, albeit an immense challenge for communities, their governments and agencies.