Засоление почв в Австралии: причины и последствия.

Soil salinity and dryland salinity are two problems degrading the environment of Australia. Salinity is a concern in most states, but especially in the south west of Western Australia. The Eastern Mallee and the Western Mallee of Western Australia are areas that are prone to salinity with little remedial action being undertaken to rectify the problem. Lands surrounding Lake Bryde East Lake Bryde and Dumbleyung Lake have also been affected. In the Murray River valley irrigation has caused salinity problems. Land surrounding the town of Werrimull in the northwest of Victoria have been affected by salinity due to land clearing.

The soil in Australia naturally contains salt, having accumulated over thousands of years. This salt may come from prevailing winds carrying ocean salt, the evaporation of inland seas, and from weathered parent rocks. When this ground water comes closer to the surface, this salt is also brought up. As the water eventually evaporates, it leaves behind all this concentrated salt, resulting in soil salinity. This can be caused by an imbalance in the hydrological cycle, or by irrigation. Prior to British settlement in 1788, groundwater levels were in equilibrium. Seasonal recharge, and year round utilisation of ground water by deep rooted native vegetation resulted in ground water levels remaining static. Land clearing in Australia has resulted in a loss of this native vegetation, replaced largely by agriculture and pasture crops. These are often shallow rooted annual plants which are unable to intercept and adequately absorb stored and rising ground water. This creates an imbalance in the hydrological cycle, and results in dryland salinity. Salinity is classified as a dissolved salt content of a substance like soil or water. Salinity can prevent crops and other vegetation from growing leaving land empty. Irrigation is also a contributor to salinity. Firstly, the addition of irrigation acts to simulate rainfall, and if not applied at appropriate levels, can result in the recharge of water tables, and promotes rises in the water table. Secondly, irrigation water itself can contain salts, which are deposited into the soil with its use. This level of salt can range from 0.5 2 tonne per hectare per year, and can greatly increase natural salt levels.

Over time this process has caused the thin top soil layers to become irreversibly salty and no longer suited for agriculture. By 1999 an estimated 2.5 million hectares of land had become salinised since the introduction of European farming methods. Currently, around 5.7 million hectares of land is classed as having 'high potential' for salinisation with that number expected to rise to 17 million hectares by 2050. High soil salt levels have dramatic impact on plant root zones, in both native vegetation as well as agricultural and pasture crops, natural wetlands and surrounding water ways. An increase in salt can decrease the ability of plants to absorb water through their roots by osmosis, cause leaf burn and necrosis through increased levels of sodium and chloride, and create nutrient and ionic imbalances resulting in poor growth and death. Salinity can also adversely affect infrastructure such as roads, buildings, underground pipes and cables through oxidation. 15% of current irrigated land is impacted, and up to 30% is currently under threat. The current cost to Victoria is estimated at $50million per year. This is expected to rise significantly with the impacts on agricultural land, wetlands and infrastructure in high risk areas to increase, mainly in part to an anticipated 10 fold increase in salt levels by 2050. 75% of water bird species in decline, a 75% reduction in sealed road life, and $400million in lost profits. It is expected to cost the state around $47million per year in lost agricultural profit, and is expected to taint more than 20% of ground water to levels above those safe for human consumption.

The Australian governments have taken an integrated approach to target different scales of management. The approach is to manage the salinity issue at national, regional and state levels, down to local and individual farmers. Since 1983 the Australian governments have actioned the National Soil Conservation Program, National Landcare Program, Natural Heritage Trust, National Action Plan for Salinity and Water and Caring for our Country. The National Landcare Program focused on improving resource management and practices at the farm and local level. The National Dryland Salinity Program (1993 to 2004), funded a broad range of research and development from which to roll out further government programs. The National Action Plan for Salinity and Water Quality (NAPSWQ), implemented together with the Natural Heritage Trust (NHT) program, ran from 2000 to 2008. The NAPSWQ was adopted through an intergovernmental agreement between Australian commonwealth, state and territory governments. The plan aimed to help support community action and land managers in adversely affected catchments, and was rolled out by regional Natural Resource Management (NRM) organisations. The governments committed $1.4 billion over seven years to tackle the salinity problem. The plan involved input and participation from government, community, local business and land managers. The NAPSWQ focused on 21 regions across Australia that were deemed; through hazard assessments and dryland salinity risk, to be most affected by salinity and water problems. The goal of the NAPSWQ was to motivate and enable regional communities in preventing, stabilising and reversing trends in salinity; improve water quality and secure reliable allocations for both human, industrial and environment use. The overarching objectives of the NHT were biodiversity conservation, sustainable use of natural resources, community capacity building and institutional change. In 2008 the initiative Caring for our Country was started to replace the National Action Plan, which had ceased. This Australian Government initiative aims to build on the work done under the NAPSWQ, focusing on a more targeted asset based approach, and aims to build attitudes of environmental stewardship.

Community based approaches have been a key feature of many regional salinity management programs in Australia. This is in response to various government initiatives, notably the National Landcare Program (1989), Natural Heritage Trust (1997) and the National Action Plan for Salinity and Water Quality (2000). This approach provides the social platform required in many cases for the successful adoption of salinity management practices. Often lacking however, is the presence of scientific skills and detailed knowledge needed to develop viable technical and economic salinity management options. Below are some examples of community based programs currently operating in Australia and their contributions to salinity management.

Landcare groups involve community members and landowners working together in a voluntary capacity to improve land management practices. In relation to the management of salinity, these groups have been effective in: raising awareness and educating the community about dryland salinity; allowing local knowledge and information to be shared in order to develop suitable management plans; developing skills, building capacity and empowering communities to address salinity issues.

There are mixed predictions in relation to climate change's effect on salinity in Australia. Climate change could potentially ameliorate salinity in Australia in some circumstances, but in others it may have detrimental effects. It is predicted that in some instances climate change will result in the reduction in annual rainfall leading to a drier and warmer climate, which will ultimately reduce salinity. Conversely climate changes impact on the salt concentration in water bodies is expected to be unfavourable. Where there is a reduction in rainfall it is expected that salinity will be reduced. This will occur as a result of the water table being recharged less often, reducing the chance of the water table transporting underground salts to the surface of the land. This is an issue as dryland salinity is onset by additional deep drainage. In Australia this will be most evident in South Australia, Victoria and the lower half of Western Australia. Austin et al. of CSIRO have predicted that water in the Murrumbidgee will drop by up to approximately 48% by 2070 which will result in salt yields on the surface of the land falling by approximately 30%, however the stream salinity concentrations are predicted to increase by 11%.