Australia: The Land Where Time Began
West Australian Wheat
The wheat belt is a area with an annual rainfall of less than 600 mm. Tributaries of 4 rivers originate in the wheat belt, the Avon River upstream from York, the Blackwood River upstream from Bridgetown, and the upper reaches of the Kent River and the Pallinup River. The salinity is high in these and other rivers, and is continuing to increase. The salinisation resulting from clearing of the native deep-rooted vegetation of agriculture is already affecting a large area, some ecosystems being devastated by the high and increasing salt load, such as streams, wetlands and riverine ecosystems. Research has led to the conclusion that as the salinity increases the area of land affected is expected to triple, or even quadruple in the future.
The estimate of the area of the river catchments of the wheat belt that is presently affected is 10 %, with a expectation that this area will rise to up to 40 % at equilibrium. Though the most serious effect on the biota is seen in the lower parts of the area, the overall flatness of the land means that the area affected is large. It has been estimated that 80 % of susceptible remnant vegetation on farms is either at risk or already being affected. On public land the figure is 50 %. The degradation is mainly on the wetland sand drainage lines, with the banks and beds of 80 % of the rivers of the area being seriously degraded. Little attention has been given to the wetlands that are already well-advanced, to the exact level of degradation is mostly unrecorded.
It has been estimated that under each Ha of land in the wheat belt there is about 10,000 tonnes of salt. While the deep-rooted native vegetation covered the area of the whet belt all was well, the watertable was kept low enough that the salt remained out of harms way. The changes in the hydrology of the area that resulted from clearing led to rising watertables, just as it did in the Murray Basin and elsewhere. Some landholder and a number of community organisations have been planting deep-rooted perennials, fencing off remnant vegetation and rehabilitating riverine corridors.
Unfortunately, assessments of these efforts to reverse the salinisation of the wheat belt has found that in discharge areas the water levels are not changed much by tree planting, and what effect there is only occurs when the water is relatively fresh. Also, in .local aquifers, it requires an area of land as high as 50-80 % of the area to be revegetated with deep-rooted species to have any significant effect.
It has been found that further from the planted area, trees have so far had not much, is any, effect on the water level. The tree planting has local effects on the groundwater, but it has been shown that to achieve significant results it is necessary to densely plant over large areas of the catchment. It also seems for any effect to show up requires periods of time in decades rather than years, making for long term projects, the results such as reduced salt load of streams, not being known for a number of decades.
Attempts have been made to reduce the salinity by pumping. The overall effect was found to be small, the greatest effect being seen in local areas, and the process is very slow. After the pumping there was a problem with the salt removed from the system
The conclusions reached by the study were the hydrological systems in the wheat belt are too flat, transmission of water is too slow and there is too much salt for revegetation to have a noticeable effect on human timescales. This makes it difficult to assess methods being tested because they take decades to have an effect, if they have an effect at all.
To change the salinity of drainage lines by pumping would require long-term pumping and the salt then has to be dealt with. One suggestion that it bound to upset a number of people, as well as entire ecosystems, is the sacrificing of several rivers, the Avon-Swan and Blackwood Rivers have been suggested, in effect converting them into salt drains.
According to White (2000), it may need changes on the scale of geomorphologic or climatic change to reverse the damage already done to the system. White suggests it may be necessary to reforest large parts of the landscape, and the use of engineering methods to keep things going long enough for the planted vegetation to take effect, and that could take many years.
Here, as in many other places, it seems Australia is not designed for agriculture of the kind practiced in other parte of the world. The Aboriginal People managed to survive for thousands of years by changing the environment enough for them to manage it sustainably by living with what they then had, instead of the European way of agriculture where the environment is continually changed to maximise the production of the crops and stock, as they had in wetter, more fertile parts of the world with younger soils that had been renewed much more recently than the ancient, worn-out soils of Australia, all without regard for the natural systems that it all depends on.
Mary E White, Running Down, Water in a Changing Land, Kangaroo Press, 2000
|Author: M.H.Monroe Email: firstname.lastname@example.org Sources & Further reading|