SoE 2003 > Land > 4.3 Induced soil salinity

4.3 Induced soil salinity

Without substantial preventative and remedial action, salinity will affect even more of the State's agriculturally productive land, streams and rural and urban infrastructure

Soil salinisation is an increasing land degradation problem throughout both rural and urban areas of NSW. Approximately 180,000 hectares of the State is currently affected by shallow watertables or dryland salinity, with most in the Murray–Darling Basin. It is predicted that without substantial remediation up to 1.3 million hectares of mostly agricultural land in the basin will be affected by 2050.

Additional funding is being applied to remediate and manage salt-affected areas through the NSW Salinity Strategy and the National Action Plan for Salinity and Water Quality.

NSW Indicators

Importance of the issue

Salinity occurs naturally in many areas of NSW, with high levels of soluble salts stored in the soil and ground water. These accumulations of salt have developed from landscape processes over thousands of years. In other areas, however, increasing salinity is the result of human activities altering the natural balance of the water cycle in the landscape. This is known as 'induced' salinity.

The removal of native vegetation through land clearing and the adoption of unsuitable land uses and practices have caused watertables to rise. This allows salts to move close to the soil surface where they are concentrated by evaporation or discharged into surface waters. Salinisation occurs when enough of these salts accumulate to cause degradation of land and water resources and vegetation.

Dryland salinity affects the largest areas, but salinity also occurs in irrigation and urban areas (see EPA 2000a for further information).

Rising watertables and soil salinisation have serious and wide-ranging environmental and socioeconomic implications. The process may operate at a local or regional scale: impacts can occur on-site or nearby at a farm level, elsewhere in the catchment, or even outside the catchment. The impacts are decreased agricultural production, damage to infrastructure, landscape degradation and a decline in ecosystem health.

At the farm level, the main impact of increasing salinity is a loss in the productive capacity of the land. Salinity also damages farm and public infrastructure, such as water supplies, roads, fences, buildings, pipes and underground systems. Severe salting makes the soil more susceptible to secondary land degradation processes, such as soil structure decline, erosion and sodicity (see 'Sodic soils' below). The salinisation of a catchment directly affects the quality of surface water downstream. Salt export to downstream waterways may place water resources, aquatic ecosystems, farm dams, riparian vegetation and wetland areas at risk (see EPA 2000a, EPA 2000c and Water 5.3).

Table 4.5 provides a summary of the key assets at risk from salinity caused by shallow watertables in the NSW catchments of the Murray–Darling Basin, which covers 75% of the State and is one of the areas most affected. The National Land and Water Resources Audit predicts substantial increases in areas affected by shallow watertables over the next 50 years, including areas currently used for forestry, nature conservation, remnant vegetation and agriculture. The largest present and future impacts will be in pastoral and cropping areas. Over 90% of the land currently affected by salinity is used for agriculture and is predicted to increase eight-fold by 2050. Urban salinity, already an issue in many towns of NSW, is likely to worsen with an almost four-fold increase by 2050 (Littleboy et al. 2001; NLWRA 2001b).

Table 4.5: Key assets at risk from shallow watertables in the Murray–Darling Basin

Source: Littleboy et al. 2001

Additionally, increasing dryland and irrigation salinisation in the Murray–Darling Basin over the last 20 years is now considered a significant source of rising stream salinity. In-stream salt loads are forecast to double in most catchments in the basin by 2050, with some river water exceeding the salinity levels set in international drinking water guidelines (Beale et al. 2000). Water 5.3 has further details.

The Murray–Darling Basin Commission and the National Dryland Salinity Program have funded a three-year research project to identify the impacts and costs of dryland salinity across the entire basin. For the NSW portion, an estimated direct cost of $151 million a year is incurred by local governments, households, businesses, State Government agencies, utilities and agricultural producers. The full cost of dryland salinity is higher than this estimate, since impacts on the environment and cultural heritage have not been included (Wilson 2001a; Wilson 2001b; Wilson 2001c; Wilson 2002a; Wilson 2002b; Wilson 2002c; Ivey ATP 2002a; Ivey ATP 2002b).

Conclusive documentation of all areas affected by salinity has not yet been completed. However, the National Land and Water Resources Audit's Australian Dryland Salinity Assessment 2000 has significantly increased knowledge about dryland salinity (NLWRA 2001b). Only limited new information is available on salinity in irrigation and urban areas.

Dryland salinity

Areas affected or at risk of dryland salinity are those where salt outbreaks have occurred or where watertables have risen to within two metres of the surface. In NSW, approximately 180,000 hectares of land are currently affected in this way. Over 90% of the affected land is in five catchments: the Murray, Murrumbidgee, Lachlan, Macquarie and Hunter. Information about dryland salinity along the coast is limited, apart from the Hunter and Hawkesbury–Nepean catchments, where around 28,000 hectares of land is estimated to be affected (Littleboy et al. 2001).

Map 4.4 uses data from the National Land and Water Resources Audit (NLWRA 2001b) to show the extent of dryland salinity in 2000. Much of the impact is in productive agricultural areas, with the most extensive stretching from Gunnedah, south through Tamworth, Dubbo, Forbes, Yass, Wagga Wagga and Albury.

Map 4.4 also shows areas predicted to be affected by salinity in 2050. At-risk areas are expected to increase to 1.3 million hectares or 1.6% of NSW. The estimates were based on measured trends in rising watertables in areas with saline ground water. Coastal catchments are not represented in the prediction due to a lack of groundwater data (Littleboy et al. 2001; NLWRA 2001b).

Map 4.4: Known and predicted extent of dryland salinity and shallow watertables

Source: Derived from NLWRA 2001b

Notes: Areas affected are based on groundwater levels and air photo interpretation. Due to limitations in the spatial coverage of available air photo and groundwater level data, it is likely there are other areas currently affected by salinity. The forecast extent of salinity was calculated using rates of watertable rise and excludes coastal catchments.

More details of the predicted changes in individual catchments are shown in Table 4.6. Two scenarios are shown with different salinity risk criteria. If the more conservative criterion of risk is used (watertable rises to < 5 metres), the area affected by 2050 rises to 2.4 million hectares or 3% of NSW (Littleboy et al. 2001).

Table 4.6: Estimated areas affected by shallow watertables in the eastern Murray–Darling Basin, 2000–2050

Source: Littleboy et al. 2001

Note: ^(a) Zero values for the Gwydir catchment reflect lack of available data rather than no risk.

Rates of watertable rise are fastest in the southernmost inland catchments and tend to decrease in a northerly direction. This suggests that the impacts of rising watertables will take longer to surface in the northern catchments of NSW (Littleboy et al. 2001). By 2020, shallow watertables will occur in large areas of the Murrumbidgee and Murray catchments, while by 2050, large areas of the Lachlan, Castlereagh and Macintyre catchments will also be affected (Littleboy et al. 2001; NLWRA 2001b).

Irrigation salinity

Over-watering and water leakage can cause watertables to rise in irrigation areas. This has occurred in some of the irrigation schemes along the Murray River, where significant areas are already affected by waterlogging and salinisation, preventing agricultural production on some land. Data on the total area affected is limited, but those at greatest risk are in the Murrumbidgee Irrigation Area near Griffith, including the Mirrool, Yanco and Colleambally Irrigation Districts; the Murray Irrigation Area around Deniliquin, including the Berriquin, Deniboota and Wakool Irrigation Districts; and Jemalong Irrigation District, west of Forbes (DLWC 2000a).

Urban salinity

Urban salinity results from a combination of over-watering and dryland salinity processes. It currently affects more than 40 towns in the Murray–Darling Basin as well as parts of Western Sydney and the lower Hunter catchment. Considerable damage is caused by salinity in these areas, affecting homes, other buildings, roads, pipes and other infrastructure (NSW Government 2000).

Sodic soils

Sodicity is a characteristic of some NSW soils which predisposes them to compaction and surface sealing, excessive runoff, and erosion if land use or management is inappropriate (see EPA 2000a). The condition is linked to salinity impacts as sodic soils are often found in poorly drained or low-lying areas where salinity problems also occur.

Although soil sodicity is less commonly known than soil salinity, it presently affects considerably greater land areas and is considered more costly in terms of its economic impact on production (NLWRA 2002). Sodic soils are widespread on the western plains of NSW and can cause severe problems for agricultural production and irrigation. Sodic subsoils are also common across eastern and central NSW, in association with specific geological formations that have high sodium or salinity levels.

Salinisation of soils can also produce sodification. Remediation of saline soils may result in sodic soils developing as some sodium will remain in the soil after the removal of free salt. Overcoming this type of sodification may prove harder than reversing the original salinity.

Response to the issue

Both the Commonwealth and NSW Governments have responded to the salinity challenge by developing strategic and integrated approaches to salinity management, backed by significant new resources.

In November 2000, the Council of Australian Governments endorsed the National Action Plan for Salinity and Water Quality (NAP) (Commonwealth of Australia 2000). NAP is a seven-year framework providing funding and coordinating a range of stakeholders, including the regional communities most affected by salinity or deteriorating water quality. NSW and the Commonwealth have agreed that NAP in NSW will also use the tools of the NSW Salinity Strategy to complement those set by NAP to manage salinity in the State (NSW Government 2000).

The agreement provides for joint funding of $396 million, with NSW contributing $198 million. The priority catchments in NSW for NAP funding are the Balonne–Maranoa, Border Rivers, Lachlan–Murrumbidgee, Lower Murray, Macquarie–Castlereagh, Murray and Namoi–Gwydir.

Progress in implementing the NSW Salinity Strategy to date includes:

• formation of six Salt Action teams, five to train extension officers working with farmers to address salinity at the paddock level in the Southern, Central West Lachlan, Central West Macquarie, North West and Hunter Coastal regions and a sixth based in Penrith to assist local government manage urban salinity
• a pilot of the Environmental Services Scheme, a market-based solution to salinity being trialled on 20 rural properties across NSW
• development of Catchment Blueprints, containing end-of-valley salinity targets
• the establishment of two major research sites in northern and central NSW to determine the hydrology of existing farming systems and the best location for remediation work to slow the effects of salinity.

The Murray–Darling Basin Ministerial Council (MDBMC) has developed the Basin Salinity Management Strategy 2001–2015 (MDBMC 2001). This establishes a framework for implementing NAP, the NSW Salinity Strategy and regional salinity and Catchment Blueprints within the Murray–Darling Basin. A key feature has been the adoption by the MDBMC of end-of-valley salinity targets for each catchment and a target site for the whole basin at Morgan in South Australia where the aim is to maintain salinity at less than 800 EC (electrical conductivity) units for 95% of the time. While in many cases end-of-valley targets allow for further rises in salinity, they are in effect a 'cap' on salinity that gives the appropriate signals for protecting key values and assets in the valleys.

Both the Basin Salinity Management Strategy and NAP have agreed to the interim NSW salinity targets, now incorporated in the Catchment Blueprints.

The National Dryland Salinity Program continues to support research, development and extension efforts for managing dryland salinity. A number of projects have provided important information for the National Land and Water Resources Audit's salinity program, including the Australian Dryland Salinity Assessment 2000 (NLWRA 2001b). This comprehensive assessment has defined the distribution and impacts of dryland salinity across Australia and will assist in developing targeted national responses to the problem.

Land and water management plans (LWMPs) have been developed and implemented by the community with the support of government to protect the environmental, social and economic values within the State's privatised or corporatised irrigation districts. These 30-year plans are consistent with the MDBMC Basin Salinity Management Strategy.

The State's farming community has employed various management practices on agricultural lands that are affected by, or at risk from, salinity. To manage and prevent salinity, NSW farmers by May 2002 had planted 91,000 trees and 1.1 million hectares of crops, pastures and fodder plants; constructed 4.3 million hectares of earthworks (levees, banks and drains); and fenced 17,000 hectares of land (ABS 2002).

The Cooperative Research Centre for Plant-based Solutions for Dryland Salinity, established in 2000, is also providing input into research projects in the areas of education and technology transfer, the function of natural ecosystems, new and improved plant species, new farming systems, and economic and social assessment.

Sodic soils

The most common treatment for sodic surface soils is the regular application of gypsum (calcium sulfate) to improve the soil structure and water infiltration into the subsoils (SCARM 1998). Only a small fraction of land with sodic soils is currently being treated in this way as the cost of treatment with gypsum is usually too high for dryland agriculture (based on current prices and returns). As a result, other agronomic options for managing sodic soils are currently being investigated by NSW Agriculture and the Department of Infrastructure, Planning and Natural Resources. These include the use of improved farming management practices, similar to those recommended for other forms of land degradation.

Effectiveness of responses

NAP and the NSW Salinity Strategy provide a more coordinated framework for salinity management than in the past and will enable investment to be focused in priority areas. The development and adoption of NSW end-of-valley salinity targets should also allow an assessment of whether the problem is improving or worsening. While it is too early to gauge the operational effectiveness of these initiatives, efforts to focus on priority areas are expected to bring greater gains. The Environmental Services Scheme is at pilot stage and it is too early to assess its effectiveness.

The NSW Government's Select Committee on Salinity reported on the adequacy of the Commonwealth's response and contribution to addressing salinity in December 2002 (NSW Parliament 2002). The report summarises a number of concerns from scientific and economic experts about the implementation of NAP including:

• a lack of adequate scientific and technical knowledge to support NAP projects
• a need to fund cost-benefit analyses of catchment management plans to determine whether they are justified on technical and economic grounds
• a need for greater cross-disciplinary scientific cooperation to understand salinity
• the inadequacy of current mapping/modelling and other on-the-ground scientific investigations needed to make informed investment decisions.

LWMP initiatives since the mid-1990s as part of the corporatisation of irrigation areas are now showing signs of contributing to environmental improvements in these areas. For example, a decline in the amount of land affected by high watertables has been reported in Murray Irrigation Ltd's area of operation, which has been attributed to reduced channel seepage, improved water use efficiency and a series of dry years (Murray Irrigation Ltd 2002).

Future directions

There are a variety of options that can be adopted to manage salinity depending on the management objectives and the local biophysical environment. A combination of these options is needed to address salinity problems at both the farm and catchment levels. Some land-use changes will be required at a catchment scale and improvements may take a long time to generate outcomes, so in some cases living with and adapting to salinity will be unavoidable.

At the farm level, more landholders can adopt better management practices, such as protecting native vegetation and changing land-use and farming practices to those which re-establish the water balance. In some instances, financial incentives are available. More information on sustainable land management practices and programs to support salinity management is available from the Department of Infrastructure, Planning and Natural Resources and NSW Agriculture.

Government agencies should continue to invest in priority areas through NAP, the NSW Salinity Strategy and Catchment Blueprints. The further development of schemes that provide ongoing economic incentives for the provision of environmental services by landholders will also help to achieve long-term land management changes.

Improved ongoing evaluation and monitoring of the natural resource base and the effectiveness of salinity management responses is also required.

Linked issues

4.1 Land-use changes

4.2 Soil erosion

5.1 Freshwater riverine ecosystem health

5.3 Surface water quality

5.5 Groundwater quality

6.1 Terrestrial ecosystems

6.3 Terrestrial species diversity

6.6 Aquatic ecosystems

6.7 Aquatic species diversity