Less than 1% of northern Australia (the drainage divisions between Broome and Cairns) is cleared or intensively used. Not only has widespread land clearing greatly decreased in Australia, but the re-establishment of woody vegetation for a variety of purposes continues. The increasing demand for wood and the increasing attractiveness of tree planting for carbon offsets can bring benefits to catchment health, but can also lead to decreases in catchment yield from higher rainfall areas. In the Murray–Darling Basin, expansion of commercial forestry plantations is expected to occur; projections indicate only very minor impacts of these developments on the total run-off reaching rivers, although local streamflow impacts may be significant.73 In Tasmania, the area of commercial plantation forest is currently about 15 000 square kilometres. Under future development, this is expected to increase by around 730 square kilometres (5%), which would lead to a decrease in run-off of 0.3%. However, in the Mersey–Forth region, where the area of commercial forest is expected to increase by 16%, decreases in run-off are likely to be up to 1.5%. The increase in commercial forest area is expected to reduce inflows to rivers by 138, 148 and 159 gigalitres per year (around 0.7%) under the wet extreme, median and dry extreme future climates, respectively. It may also have a small impact on inflows to, and outflows from, hydro-electric power stations (mostly concentrated in the Mersey–Forth region).
With the loss of streamflows in the South-west Coast division, a trial has begun in the Wungong catchment to see whether catchment thinning in the jarrah forest can increase water yields while reducing the likelihood of forest collapse due to climate change and improving streamflow for in-stream fauna.15 Thinning using increased fuel reduction burns in banksia woodland on the Gnangara Mound has also been investigated as a means of increasing recharge and groundwater levels that support through-flow wetlands. The increases in recharge are modest and may not justify the increase in risk to species that are sensitive to fire.
Australia has had only very limited success in the local control of animal pests that threaten inland water ecosystems, with no complete eradications from the continent. There has been more success in controlling local populations of weeds, but eradication is again elusive and depends on early identification of infestations and prompt action. It is difficult to foresee any significant reduction in the risks to water ecosystems from pest and weed species with current technologies.
The emerging developments of coal-seam gas resources in Queensland and New South Wales involve the extraction of water from coal seams. The discharge and management of this (often saline) water presents an immediate issue for land and water environmental health. In the longer term, reduced regional groundwater levels have the potential to result in diminished streamflows. Given that Australia has little experience with large-scale development of these resources, uncertainty surrounding the potential environmental impacts and their effective mitigation hampers both community confidence and environment approvals. Coal-seam gas already supplies a significant fraction of the natural gas market of eastern Australia and most of the Queensland market. Agreements are in place for exports of more than 3.6 million tonnes of liquid natural gas per year, worth more than $60 billion over the next 20 years. In June 2010, Queensland established a Coal Seam Gas Water Management Policy to ensure salt resulting from developments does not contaminate the environment.