Australia Yearbook - 2001

Chapter 14—Environment 591
14.19 FACTORS THREATENING BIODIVERSITY IN AUSTRALIA
Threat
Habitat loss and fragmentation
Introduced pests and weeds
Altered fire regimes
Altered hydrological regimes
Roads
Accelerated global warming
Other threats
Description
Cropping, forestry, mining, grazing, and human settlements have dramatically changed
vegetation cover (State of the Environment Advisory Council 1996). 60% of birds and
80% of mammals listed as threatened have declined as a result of habitat loss.
Introduced species in Australia include 25 mammals, 37 birds, 8 marine fish,
21 freshwater fish and 3,000 weeds. They threaten ecosystems by altering resource levels,
community composition, disturbance regimes and the physical environment (Mackey et al.
1998). See the section Marine pollution for exotic marine species.
Before European settlement, fire was used by Aborigines for many reasons including
regeneration of food plants. Fires varied in location, season and frequency. Current fire
regimes have contributed to the dramatic loss of small to medium sized mammal species
from semi-arid/arid environments of Australia’s arid interior.
Large water storage facilities and small farm dams reduce annual streamflow, having a
marked effect on aquatic ecosystems. Physical barriers such as weirs prevent fish from
migrating, while alteration of natural river channels removes important aquatic habitats.
See the section Effects of water resource development on Australia’s freshwater
environments.
Road construction increases sediment load in nearby waterways, affecting aquatic
ecosystems and their flora and fauna. Roads provide conduits for the movement of feral
predators and can pose barriers to movements of animals. An estimated 5.5 million frogs
and reptiles are killed every year on sealed roads in Australia.
Many scientists believe that global atmospheric temperatures are likely to rise between
1.5 and 4.5°C in the next century (Mackey et al. 1998). As this occurs, the preferred
climatic conditions for a species will shift to higher altitudes and latitudes. Survival will
depend on the ability of a species to relocate and availability of habitats.
Pollutants such as chemicals, sewage, fertiliser and heavy metals particularly affect
freshwater and marine ecosystems. See the section Marine pollution.
Salinity is discussed in the section Land degradation.
Ground water use by humans has altered flora and fauna in arid and semi-arid Australia.
Fishing, trawling and dredging have significant impacts on marine biodiversity.
Source: Based on Mackey et al. 1998.
Management of Australia’s
inland waters
Developing a reliable water resource in the early 1900s
Fifty per cent of Australia receives an annual
rainfall of less then 300 mm and is categorised
as arid or semi-arid (see Chapter 1, Geography
and climate). A dominant characteristic of
semi-arid environments is variable rainfall
patterns, within and between years. Low annual
rainfall, coupled with high temperatures,
produces high evaporation rates and low annual
runoff by world standards (Davies et al. 1994).
In the late 1800s dams were constructed to
modify the highly variable flow regime of
semi-arid river systems. The construction of
dams and weirs ensured that Australians had a
reliable water resource for both domestic and
economic purposes.
The Murray River was the lifeblood of many
early settlements and was one of the first major
river systems to become regulated. Irrigation of
agricultural land with Murray River waters in
Victoria commenced in the 1870s. As the
demand for water increased, disputes arose
between States over the distribution of the
variable resource, leading to the
commencement of the Murray River water
agreement in the early 1900s. This agreement
saw the construction of dams on the Upper
Murray and at Lake Victoria, as well as 26 weirs
and locks from Echuca in Victoria to
Blanchetown in South Australia. These
developments on the Murray and the nine weirs
built on the Darling and Murrumbidgee Rivers
as part of the Murray River agreement ensured a
reliable water resource in this region (MDBC
1990).