The Murray-Darling Basin (MDB) is considered to be the “breadbasket” of Australia; roughly the size of France and Spain combined, it houses 43 percent of the country’s farms (UNCCD 2009). An ongoing drought has been incessant for the past 7 years, reducing precipitation perilously in what is already a low-nutrient ecosystem and decimating both crops and livestock (Draper 2009).. The Murray-Darling Basin provides water to roughly 65 percent of the country’s agriculture (Draper 2009).. The major impacts are on the agriculture industry, the local farming communities, and the national economy and they are all equally as worrisome. The impacts of reduced land productivity, soil salinization, acidification and erosion, increased evaporation and runoff and loss of biodiversity are troubling and under-studied. These phenomena play into a feedback cycle that reduces precipitation, and alters negatively the hydrological cycle of the rain when it eventually falls. Some health impacts include pollution of waterways, ground water, and air pollution from dust. Furthermore, as many believe theses climactic changes are linked to global warming, the future outlook for this region is certainly not positive.
The Murray-Darling Basin - Australia.
The Murray River and the Darling River flow together in a catchment called the Murray-Darling Basin (MDB). The MDB provides 65 percent of all the water used for the country's agriculture and is the only water source for Adelaide, the fifth most populous city in Australia (Draper 2009).
The current dry spell has been gripping the region for 7 years; the longest period in the 117 year-old weather record of the country (Draper 2009).
The MDB system is home to 43 percent of Australian farms. In 2009 its usable water storage was at 16 percent of capacity and 73 percent below the normal range for this time of the year, according to the Murray-Darling Basin Authority. (UNCCD 2009).
The environmental degradation occurring in the MDB includes salinity, land degradation and loss of biodiversity (Prasad and Khan 2002).
The MDB is home to 2 million Australians, 50 percent of the Australian sheep population and 25 percent of the country’s cattle. It accounts for 75 percent of Australia’s irrigated land and approximately 10$ billion Australian dollars in agricultural production, 1.6$AU billion from mining, 3.44$AU billion from tourism and another 10$AU billion from manufacturing (70 percent of which is linked to agriculture) (Prasad and Khan 2002). These figures frame the devastation caused by the drought-driven land degradation in this basin.
The MDB, which is 14 percent of the continent’s area, has 20 major river valleys, with 30,000 wetlands. It provides a habitat for countless species of animals, including 35 endangered bird species and 16 endangered mammals (Prasad and Khan 2002). The repercussions of land degradation here are not only socio-economic but also damaging to biodiversity and the natural landscape.
Climate is the primary driver of dryland degradation in the Murray-Darling Basin. National Geographic magazine recently ran an article in which the current drought was said to be the longest one observed in the 117 year-old weather record (Draper 2009).
The MDB is a low energy hydrological system, with low potential for cleansing itself of salts or sediments. Most of the salt in the streams is not flushed out in the ocean, but rather redistributed downstream to floodplains as well as agricultural land (Connell and Grafton 2007).
The vulnerability of the MDB to degradation is exacerbated by two natural elements of variability. Local variability in the basin exists because of a vast range of climactic conditions that go from rainforest in the humid highlands of the east of the basin to arid lands in the south-western area of the basin (Maxino et al. 2008; Prasad and Khan 2002). Furthermore, inter-annual climate variability conditions the amount of rainfall and, in a more complicated mechanism, the amount of runoff in the catchment (McMahon et al. 1992).
Irrigation and unsustainable land use are the two primary local anthropogenic sources of stress on the MDB, which cause land degradation (Maxino et al. 2008). Irrigation needs in the catchment have led to the development of a system of storages, leading to artificial flows in the river system and impacting biodiversity as well as the potential for agriculture in the future (Prasad and Khan 2002). Extensive clearing and land cover transformation in the basin have also dramatically increased runoff and rainfall leaking through soil directly to the groundwater supply; the resulting rising groundwater levels are then directly culpable for the deteriorating soil salinity problems that inhibit land-use (Prasad and Khan 2002).
Inappropriate land practices have also been linked, indirectly through the process of salinization, to the sulfur pollution of wetlands (Hall et al. 2006).
Irrigation and unsustainable land use are the two primary local anthropogenic sources of stress on the MDB, causing land degradation (Maxino et al. 2008).
Inappropriate land practices have been linked to the process of salinization, which in turn has been linked to the sulfur pollution of wetlands (Hall et al. 2006). Sulfidic sediments are formed when sulfide compounds are reduced to sulfide by anoxic bacteria that is in the presence of organic carbon within a body of water. Sulfides are toxic to aquatic organisms and can produce noxious odors. When the sulfidic sediments are exposed to oxygen in the air, they oxidize and produce an acid, which, if flushed back into a waterway can be lethal to aquatic organisms (Hall et al. 2006). Given the occurrence of droughts in the vast wetland area of the Mallee (a typical scrubland vegetation in southern Australia), acidification and anoxia of the wetlands is a major concern.
The main impact is the lack of irrigation potential due to drought and land degradation processes. The economic impact on agriculture and livestock industry, given the importance of the MDB, is a national concern (Prasad and Khan 2002). The environmental degradation occurring in the MDB includes salinity, land degradation and loss of biodiversity (Prasad and Khan 2002).
The drying of the vegetation in the MDB exposes the system to fire; another negative feedback mechanism at play in the system. The drier the vegetation is, the easier it burns and the likelihood of expansive uncontrolled bush fires increases. The cleared land is then exposed to runoff, flushing sediment, nutrients and salt in the waterways. However, once the vegetation grows back there is a different problem: the initial vigorous growth of the plants draws all the moisture it can from the soil, requiring more water than the previous adult vegetation needed, and exacerbating the effect of drought and soil salinization (Mark Adams and Geoffrey Carey, ABC 2009).
Wetlands provide the ideal conditions for the formation of sulfidic sediments. In a famous case in Bottle Bend, S. Australia, the wetland was recorded as having a Ph level of 3, resulting in substantial fish deaths. Furthermore, the researchers linked this phenomenon to salinization, another worrisome process within the MDB. The elevated sulfur in the wetland was attributed to high levels of salinity in the groundwater (Hall et al. 2006).
Projections of future increased climactic inter-annual variability do not allow for a positive outlook on the resolution of the environmental and hence socio-economic impacts.Notwithstanding the current climate, local vulnerability and the issues with land-use practices in the MDB, in 2006 van Dijk et al. identified climate change as being the biggest threat to the basin’s hydrology, with the potential to reduce stream flow by 5 percent within 20 years and 15 percent within 30 years (Maxino et al. 2008; van Dijk et al. 2006).
The climate change in the Basin is likely to result in higher maximum and minimum temperatures and a reduction of winter and spring rainfall,which together with an increase in evapotranspiration is likely to reduce the water availability in the Basin. (Prasad and khan 2002)
A government council has been has been at work in providing funds to the MDB in order to rectify the current water diversion from the river system to the irrigated lands.Since one of the main drivers of degradation has been this unsustainable water diversion, it is agreed by many that reinstating a natural environmental flow to the river will aid in making the MDB once again a healthy working river system (Prasad and Khan 2002).
Billions of dollars have already been spent by the Australian government in plans to remediate the current unsustainable land use practices which lead the salinization problem.The National Action Plan for Salinity and Water Quality and the Natural Heritage Trust Scheme are the main funding sources. In 2007 the Australian government announced the “National Plan for Water Security” with a 10$AU Billion planned investment over 10 years. The MDB was the primary focus of the plan (Prasad and Khan 2002; Connell and Grafton 2007).
UNCCD press release. 6 November 2009. Unpredictable and extreme droughts threaten food security. http://www.unccd.int/publicinfo/pressrel/showpressrel.php?pr=press09_02_09 (Last accessed 6 November 2009).
Draper, R. National Geographic. April 2009. Australia’s Dry Run. http://ngm.nationalgeographic.com/2009/04/murray-darling/draper-text/2 (last accessed 6 November 2009).
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McMahon, T. A., B. L. Finlayson, A.T., Haines, R. Srikanthan. 1992. Global runoff: continental comparisons of annual flows and peak discharges. Catena Verlag, Cremlingen-Destedt: West Germany.
Hall, K. C., D. S. Baldwin, G. N. Rees, A. J. Richardson. 2006. Distribution of inland wetlands with sulfidic sediments in the Murray-Darling Basin, Australia. Science of the Total Environment 370: 235-244.
van Dijk, A., R. Evans, P. Hairsine, S. Khan, R. Nathan, Z. Paydar, N. Viney, L. Zhang. 2006. Risks to the shared water resources of the Murray-Darling Basin. Murray-Darling Basin Commission: 49. Canberra.
Connell, D. and Grafton, R.Q. 2007. Planning for water security in the Murray-Darling Basin. Economics and Environment Network Working Paper. EEN0705. Australian National University. 9 August 2007.
Encyclopedia of Earth. 21 March 2007. Murray-Darling woodlands and mallee. In: Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [Published in the Encyclopedia of Earth March 21, 2007; Retrieved November 4, 2009].
Geoffrey Carey. Interview for ABC Australia. Fire, Flood and Acid Mud. May 1st 2009. http://www.abc.net.au/catalyst/murraydarling/ (Last accessed 6 November 2009).