Australia's environment in context (Land and water systems - an historical perspective)

Independent Report to the Commonwealth Minister for the Environment and Heritage
Australian State of the Environment Committee, Authors
CSIRO Publishing on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06745 0

Australia's environment in context

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Land and water systems - an historical perspective

Significant environmental degradation has occurred to land and water systems in Australia. Despite numerous examples of good irrigation practice, tillage systems and pasture and rangeland management, enormous areas are still suffering from damage, and large areas are being degraded or are under threat of degradation in the future.

Parliamentary debates, media reports, recommendations from inquiries, and first-hand accounts by landowners, travellers, scientists and government officials all attest to abuse of the land (and to a lesser extent, the sea) since 1788. Indigenous peoples had over many thousands of years developed a spiritually based relationship with the land, even as modified through the use of fire. European occupation quickly transformed the landforms, soils and biota. Research and observations, in the Northern and Southern Tablelands of New South Wales, demonstrated how quickly grazing pressure in the 1830s and 1840s induced slope instability and soil loss. Although such effects were quickly identified, they persisted and grew with consequences that remain with us.

Ignoring lessons has become a characteristic of Australian natural resource management. It is only in the last 30 years that many Australians have developed a renewed commitment to a conservation ethic. Yet what has emerged is a very complex and contradictory set of attitudes and processes. Some economic and social imperatives require individuals, communities, financial institutions and governments to give priority to wealth creation, whereas there is a powerful and growing desire to pass on to the next generation a land in better shape than was inherited. It is increasingly recognised that individual interests, operating through the exercise of property rights in a market economy, cannot be the sole mechanism for ensuring sustainability.

The condition of the settled coastal strip of Australia with its hinterland catchments and forested areas is heavily affected by population growth, localised intensive resource use and booming recreational demands. Continued conversion of land to freehold and division into ever smaller parcels, has meant that the remaining Indigenous heritage places within this zone are significantly threatened. Results of an initial qualitative assessment of 972 of Australia's estuaries show that heavily populated parts of the south-east coast, the south coast and Bass Strait, the South Australian gulfs and south-west Western Australia show a concentration of modified or severely modified conditions.

 

A small sediment-loaded stream with steep banks, typical of active accelerated gully erosion

A small sediment-loaded stream with steep banks, typical of active accelerated gully erosion

Source: Ann Hamblin.

About 50 000 km of streams have been degraded by sand deposition, mainly in south-east Australia. Sediment is moving off hill slopes much faster than soil is formed, an obvious problem for those areas seeking to sustain agricultural or forestry yields. Sediment movements modify habitats along watercourses, lakes and estuaries, and deliver suspended sediment to inshore coral reefs of the Great Barrier Reef region with localised loss of coastal seagrasses and associated habitats of inshore species.

 

 exacerbating native vegetation loss, increasing soil erosion

Salinity: exacerbating native vegetation loss, increasing soil erosion

Source: Peter Richardson, CSIRO Land and Water.

Maintaining the economic, social and environmental health of the intensive land use zone south from central Queensland through New South Wales and Victoria and into southern parts of South Australia and the wheatbelt of Western Australia poses formidable problems. Although these zones embrace some of the most productive and agriculturally efficient arable lands in Australia, major stakeholders such as the NFF, the ACF and all levels of government recognise the need to address the adverse conditions which affect the region's long-term sustainability. Many factors contribute to this dismal prognosis as discussed in the Land, Inland Waters and Biodiversity theme reports.

According to the Prime Minister's Science and Engineering Innovation (PMSEI) Council (1998) the spread of salinity and its highly adverse consequences typifies the threat to the economic and environmental sustainability of whole rural communities. Since that report was released, the National Land and Water Resources Audit (NLWRA) (2001a) has released their dryland salinity assessment in collaboration with the states and territories. This assessment, which described the distribution and effects of dryland salinity across Australia, estimated:

  • about 5.7 million hectares, mostly in the agricultural regions, are at risk of or are affected by salinity, potentially increasing to 17 million hectares in 50 years
  • up to 20 000 km of inland waters could be salt affected by 2050
  • up to two million hectares of native remnant vegetation could disappear over next 50 years
  • at least 200 rural towns could experience salt damage over the next 50 years.

The PMSEI Council (1998, p. 11), further noted that:

There are clear market failures in that the costs of degradation to downstream users and to the environment, where known, are not borne by those benefiting from the upstream exploitation of the landscape. In many cases the costs will be borne by future generations. Rational market behaviour at the enterprise level will cause (and has caused) serious and irreversible offsite impacts to biodiversity, rural infrastructure and downstream water users, as well as causing unnecessary hardship to landholders.

The major governmental response to the long-term risk posed by dryland salinity has been the NAP for Salinity and Water Quality (Commonwealth of Australia 2000), reported in the Land and Biodiversity theme reports.

Salinity reflects only one of many problems facing the agricultural regions. Soil acidity, soil erosion, land clearing, weed infestation, pesticide contamination, habitat modification of land and water areas, and loss of river flows all have severe local and regional effects.

 

Weeds of national significance include Prickly Acacia

Weeds of national significance include Prickly Acacia

Source: QDNR.

Between 1995 and 2000 a cyclic return of good rainfall (La Nia) conditions has promoted vegetation, pasture and crop growth. The number of sheep has dropped, and rabbit populations reduced substantially following the escape and spread of RCD in 1995.

The cyclical benefits of good seasons on vegetation cover in the semi-arid areas of Australia over the past five years are also noticeable. Biodiversity has been assisted by the demise of rabbits and there has also been a small reduction of 3.7 million hectares (1.4%) in the total area of grazed leases. Where leases have been purchased by mining companies, Indigenous owners, or for conservation purposes, destocking has generally occurred. However, some areas are still overgrazed with owners attempting to maintain or increase stocking rates to protect income. Wind erosion is often accentuated in such circumstances. Feral animals and weeds provide further cause for concern over many areas. The marginality of many of these lands raises the option of compensating landholders to manage for biodiversity not for production.

Drowning in a dry landscape

Appreciating how water flows through and under our landscapes is crucial to understanding why some of our major environmental issues will take decades to solve or stabilise.

Crops and pastures have replaced native vegetation in many areas. They have shallow root systems that do not use nearly as much of the rain and the irrigation water that percolates into the soil as do native plants and trees.

Rain or irrigation water that is not taken up by plants or trees either finds its way slowly to the water table (groundwater) or moves laterally underground to adjacent streams. Because crops and pastures use less water, the excess water finds its way to the groundwater up to 10 times faster.

Consequently, groundwater levels slowly rise, and in so doing dissolve the natural salt in the weathered soils found over vast areas of Australia.

It can take from 10 to 100 years for these changes to bring salt to the land surface or to the streams. The nature of the landscape, the depth of groundwater, the amount of rainfall and irrigation and the amount of a catchment that is cleared influence the time for salt to become apparent.

Halting or reversing the rise of groundwater requires farming systems with similar water use outcomes to those of vegetated landscapes with deep-rooted plants and trees. Such changes are complex and we are still looking for the appropriate mix of land uses in the many land systems that exist in Australia. What is certain is that such systems of water balance at a catchment and subcatchment scale are essential if salinity is to be managed.

Even when changes to land use like this are made, it will take many decades or even centuries to reverse the rise in groundwater levels and improve the water balance.