Grave salinity threat confronts Queensland, Australia, say researchers

According to the CSIRO, there is evidence that the rate of land clearing has accelerated to one million hectares every two and a half years, including a 26% rise in the rate of clearing of remnant native vegetation. This means that a robust analysis of the salinity hazard needs to be done in order to identify the regions facing the greatest risk, and as a basis for good policy and practice in vegetation management, says Dr John Williams, Deputy Chief of CSIRO Land and Water.

“There is widespread salt accumulation in the Queensland landscape,” said Williams. “Some salt comes from rocks, particularly ancient marine sediments, but most drifts from the sea onto the land in rainfall. Salt has accumulated over time in vast tonnages throughout the landscape. In a land mass as old and flat as Australia, subsurface drainage is poor, and salt builds up in the soils and groundwater. Queensland, with its humid coast adjacent to large semi-arid areas, provides an ideal environment for storing salt in the landscape.”

Dr Williams says there is a common misconception that the seasonal patterns of evaporation and rainfall in Queensland means that the land clearing will not lead to an increase in the amount of water draining into the subsoil, collecting the salt and carrying it to rivers and wetlands.

“There is no scientific evidence for this perception,” says Williams. “In fact, there is good evidence that the rainfall patterns in Northern and Central Queensland – where the summer or wet season rainfall is concentrated between December and April – behave in a similar way to the winter rainfall patterns of southern Australia, where salinity is widespread.” The CSIRO researchers say they have sufficient information to establish that there are large accumulations of salt in the landscape of many regions of Queensland, and that clearing will increase the amount of water draining beneath the root zone by as much as 10 times.

Huge salinity problems are currently being faced in the Murray-Darling Basin in South Australia, caused by mistakes made before the consequences of land clearing were understood, says Williams.

“The degree to which salinity will develop and the time it takes to occur will vary from place to place, but all the factors that contribute to salinity hazard exist throughout the State,” says Williams.