Australia State of the Environment Report 2001 (Theme Report)
Prepared by: Ann Hamblin, Bureau of Rural Sciences, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06748 5
Secondary salinity and acidity (continued)
Recent national initiative [L Indicator 3.5]
In 2000 the Commonwealth Government announced a broad ranging initiative to tackle dryland salinity and deteriorating water quality in key catchments and regions across Australia. This plan builds on the work established under the Natural Heritage Trust, Murray-Darling Basin Commission, state and territory strategies, and the COAG Water Agreement (AFFA 2001).
The plan reflects the sentiments expressed in a discussion paper on developing a national policy on natural resources published by the Commonwealth, state and territory governments in 1999 (AFFA 1999). This paper put forward the view that Australians must fundamentally change the way in which they manage their natural resources, and work together in partnership, across public and private sectors, jurisdictions and vested interests. Responses to the paper showed that many Australians concurred that future management would need a range of activities and policies that could tackle economic, social, biophysical and legislative change together.
Southern Australian regions have been most affected by salinity because they have been cleared for a longer time, and have been better documented than areas north of latitude 30south-west of the agricultural belt since the 1920s, it was not until the 1980s that the seriousness of the extent, or agreement on the importance of vegetation as a control measure was accepted. The following two case studies illustrate how government, scientists and the community have joined in concerted efforts to control further deterioration.
Scientists in Western Australia called attention to the problems of secondary salinity, and identified its cause, as early as the 1920s, but their concerns went unheeded until the late 20th century. Change came as results of the very extensive clearing program for agriculture in the 1950s and 1960s became apparent by the mid-1970s. This is a remarkably short response time compared with the slow rate of groundwater movement in south-eastern Australia, where the results of clearing from the 19th century only became apparent on a large scale some 70 years later. By 1980 increased research effort into methods of control concluded that engineering solutions would not be effective, and that replacing vegetation lost would be the only long-term solution (Government of Western Australia 1980). Although agricultural land development and wholesale clearing was stopped in the early 1980s, the scale of restorative action needed to halt continued encroachment was not appreciated until the mid-1990s, when the government released a Salt Action Plan (Government of Western Australia 1996). By then it was realised that encroaching salinity was affecting not only land, but river systems, biodiversity in wetlands and, a number of regional towns in the wheatbelt.
Pinpointing where current secondary salinity is located, mapping its rate of encroachment, and estimating where it will extend to in the future is being provided to land managers by Land Monitor. This consortium of agencies brings together remote-sensing information on vegetation and bare saline ground distribution, monitoring the changes over time, and relates these to hydrological domain modelling.
By using expert-system decision-tree rules, the models interrogate fine-scale digital elevation models of the landscape, to plot the estimated extension of salt in the surface soil from present locations (Figure 57). On this basis, 2.7 million hectares (10% of land) is estimated to be saline (either bare or with salt in the surface soil). (Note that this method does not distinguish between primary and secondary salinity, as the initial remote-sensing coverage is not available prior to 1988, well after the main period of land clearing.)
The area at risk of dryland salinity in south-western WA has very recently been estimated as nearly twice this amount-4.3 million hectares (16% of land)-and is predicted to rise to 8.8 million hectares (33%) by 2050 (NLWRA 2001a). The risk estimates are based on groundwater depth and the trend in changes to shallow water tables.
Figure 57: Areas at current risk of dryland salinity in south-western Western Australia.
Source: NLWRA (2001a)
Most of the current salinity and risk of salinity is in the eastern wheatbelt, in valley floors and adjacent areas. Further expansion is expected to be predominantly in the southern coast and Great Southern regions, but may also spread to the western coastal plain where the majority of the population reside.
Cranbrook is located north-west of Albany on Western Australia's southern coast, in a region with 480 mm rainfall. The little town is located in a system of low crests, undulating plains and swampy floors, with overall low relief. It is in the upper part of the Cranbrook Creek catchment. Since settlement and partial clearing of the surrounding landscape, surface drainage has increased, but water pools in many local depressions, contributing to groundwater rise. Hydrological bore studies carried out in 1997 showed that annual rates of recharge are between 0-170 mm a year in the surrounding agricultural lands, with an additional 85 mm in the townsite itself because of runoff from roof tops, roads and other sealed areas.
Once the hydrological studies had identified the scale and rate of salinity increase, management options were formulated. These include management of surface runoff in the town by drains into downstream creeks, capture of rainwater from roofs, lining of street drains and open soaks, and concreting the main town channel in parts to stop water spreading out. Also in the town, septic tanks need to be linked to a sewer system, and no new septic tanks built. Other actions needed include revegetating vacant land with fast-growing trees and lucerne to act as local pump sites, planting street trees, no further clearing of native vegetation, and fencing out remnant vegetation from stock. Agricultural areas surrounding the town also required remedial action.
Since the study was undertaken only a small amount of progress has been recorded. Some tree planting has been undertaken and inundated areas around the town have been drained, but few of the other recommendations have been implemented. Of these, the most pressing are improving the drainage of open drains and lining the Cranbrook channel and other runoff areas (Ferdowsian pers. comm.).
Figure 58: Existing saline areas and potential increased areas in the Cranbrook region.
Source: Ferdowsian and Ryder (1997)
At a quite different scale, the salinity situation in the Murray-Darling Basin was assessed in a comprehensive salinity audit (Murray-Darling Basin Ministerial Council 1999). Many of the findings were disturbing, and unexpected. The most threatening form of salinity increase will be dryland salinity expansion, rather than from groundwater rise under irrigation areas. Before the audit it was thought that most of the river salinity problems were concentrated in the lower river sections of the Murray, but the audit showed that many of the upper tributaries in northern New South Wales and Queensland have rapidly rising salinity concentrations, and are likely to rise at much faster rates than those of lower catchment rivers.
The Ministerial Council of the six governments involved has therefore developed a basin-wide Salinity Management Strategy, released in September 2000, which will put in place a comprehensive set of control measures throughout the catchments of the whole basin to tackle this issue. The potential effects on salinity levels at Morgan in South Australia and in the Gwydir Valley in New South Wales if no action is taken are shown in Figure 59. After community consultation it is intended to implement the strategy in 2001 (MDBMC 2000). The strategy has four aims:
- to protect water quality equally for all users-urban, recreational, environmental, industrial and agricultural,
- to control salt loads with a cap on the end-of-valley levels for all catchments,
- to control land degradation and preserve biodiversity, and
- to identify and allocate responsibilities for implementing, managing and monitoring the operations.
The strategy documents bluntly admit the extent of the challenge facing the Council and Commission. Many changes must be made in land and water use, management practices, funding and investment. The alternative will cause the slow decline and death of many ecosystems, inland towns, and 40% of Australia's agricultural wealth, and have a profound impact on the whole economy.
The principal actions that need to be taken are:
- putting a cap on the amount of salt flowing from every tributary into the main channels to keep river salinity at Morgan at the present level (800 EC for 95% of the time),
- providing a system of credits and debits to enforce this cap,
- creating an investment bank for revegetation, land use changes and other resource investments (such as salt works, saline agriculture, plantations),
- creating additional salt interception works to buy time,
- increase research and development on new land uses and land use practices that utilise more drainage water, while maintaining clean runoff water, and
- implementing much greater adoption of best irrigation, cropping and grazing practices.
Figure 59: Predicted increases in water salinity if no action is taken
Note: 800 EC units is the World Health Organization's desiraable drinking level, and 1500 EC units is the threshold for irrigation water quality except for very salt-tolerant plants.
Source: adapted from MDBC (1999)
Salinity has very recently been highlighted by the Commonwealth government as a major threatening process. The area of land directly affected by secondary salinity is relatively small, but the impact on water resources is already very substantial and is going to become much worse. Salinity is a 'keystone' indicator of many other types of disruption to hydrological and nutrient balances. Acid soils are having as much effect on dryland salinity as vegetation clearing through leakiness, but are affecting much larger areas.
An integrated approach to controlling dryland salinity should make use of the conventional benefits that adequate liming and fertilising can provide in increasing water use by increased plant production. Many farmers have not adopted these simple agronomic practices even under present management systems, yet they are often easier to implement and provide profits more readily than such new systems as plantation forestry. A balanced policy would encourage tree planting in addition to, not at the expense of, encouraging better water uptake by plant growth with current systems.
It is now widely recognised that 'business as usual' is not an option for natural resources management in Australia. Finding the best way forward, however, has been and still is a struggle. Initially the expectation was that technical (often engineering) solutions would solve problems such as salinity. However, it has now became clear that the scale of the issue is so large that engineering could never be the only solution.
Vegetation replacement is part of the solution, but despite all the best endeavours we still are not keeping pace with loss and removal. It is now clear that changes in people's attitudes, values, behaviour and social goals are all needed. This means action across areas of law, taxation, commerce, education, media communication, and more. The current proposals to devise acceptable but variable targets for catchment outfall values, and to set thresholds for compliance, all require social and economic change. Pannell (2000) makes the point that there are many hidden assumptions and fallacies in the way that governments and scientists have approached 'solutions' to salinisation that have held back effective treatment. The time for action is now.