Balancing Consumptive and Environmental Water Use –An Australian Perspective - Water and Agriculture: Sustainability, Markets and Policies - page 176

3. Degraded waters and water-dependent ecosystems
Healthy rivers are important for water supply, irrigation and for aquatic biodiversity.
Wetlands contribute to biodiversity and aid in groundwater recharge, water filtration and
nutrient retention. Changes to rivers and wetlands are linked to the intensity of land use,
invasive species and increases in sediment and nutrient loads. Widespread irrigation and
extraction by other water users has placed the natural ecosystem under considerable
pressure. Many of Australia's waters and water-dependent ecosystems are under
considerable environmental stress. A snapshot of the water-related issues facing Australia
and the challenges they present is provided in this section.
Loss of biodiversity
Australia is one of 17 megadiverse countries, countries with an exceptional total
number of species and a high degree of endemic species found exclusively in that country
(ABS, 2003). To illustrate, the Great Barrier Reef in northern Australia contains about
2,000 reef and 500 coral species, the highest concentration of the world's fish and coral
species.
The loss of biodiversity is considered one of the most serious environmental problems
in Australia (ABS, 2003). Key threats identified include dryland salinity, pollution,
nutrient loading and sedimentation of waterways and coastal areas, and altered
hydrological regimes. All can be partly attributed to agricultural activity and water
management.
Australian's water resources sustain 64 wetlands of international importance and over
850 of national importance. Of these, 80 of are affected by salinity, and this figure could
rise to 130 by 2050 (DEH, 2001). The number of threatened native fish species has
increased substantially in recent years, with approximately 210 listed in 2001 (AFSB,
2005). Furthermore, approximately 630,000 hectares of native vegetation are at risk from
salinisation (NLWRA, 2003).
Declining water availability
Increasing pressures to extract surface and groundwater for human use are leading to
continuing deterioration of the health of water bodies. Approximately 26 per cent of
Australia's surface water management areas are close to or have exceeded sustainable
extraction limits (DEH, 2001). This pressure is particularly strong in Australia's south
east, where the Australian population and agricultural industries are concentrated.
Rising land salinity
Land and water are essential for agricultural production. Currently around 456 million
hectares, or 59 per cent of land mass, are used for agriculture, making it the dominant
form of land use.
Salinity is the build-up of salts in the soil. While salinity is a naturally-occurring
condition of Australian soils, it has been exacerbated by agricultural activities (ABS,
2003). In 2002, two million hectares of agricultural land were showing signs of salinity
(ABS, 2002). Agricultural activities exacerbate both dryland and irrigated salinity. The
clearing of native vegetation for planting of modern agricultural and grazing species is the
major cause of dryland salinity. When deep-rooted native vegetation is replaced by crops