A main premise of the following guest post from Boxer* is that across the West Australian wheatbelt, water tables are showing an upward trend. Boxer explains the problem and the need to act now if we are to learn from history and avoid the problems that destroyed, for example, agriculture in the valleys of the once fertile Tigris and Euphrates Rivers.
I have asked Boxer for a link to some data that quantifies the extent of the rising water table problem. He has responded that:
There is no single place that I can find where a large amount of water table data is assembled in one place. This is not because there is a paucity of data, but I think because there is so much data, and the fundamental cause and effect of dryland salinity has been so well established for so long, that the publications over the last decade or two do not directly present water table data. The scientific debate has moved on.
If a problem is complex and widespread, all the more reason, in my opinion, to have a few agreed indicators and regularly report on how they are trending. Others may see things differently? The issue is important. Let's have some discussion. Here's the post:
Like a number of other people who comment on this blog, I enjoyed Jennifer's recent piece on Ockham's Razor (ABC Radio, http://www.abc.net.au/rn/science/ockham/stories/s1509193.htm ) in which she addressed the arguments of various doomsday prophets such as Tim Flannery and Ian Lowe.
The Prophets of Doom have a list of iconic issues. I think it is healthy for the Prophets to be challenged because they have a vested interest in, for example, arguing that climate change will be the end of all things, just as coal miners have a vested interest in business as usual. Challenge them both.
On the issue of salinity however, I argue that dryland salinity is a major issue for this country. On this one, I am with the doomsday crowd. My vested interest? My professional life is bound up in finding ways for agriculture to adapt to rising water tables and perhaps even find ways to prevent the problem becoming as bad as the models predict.
Jennifer uses the example of the Murray River, where, at a point just upstream from the off-take for Adelaide's water supply, salinity levels have fallen over the last couple of decades due to salt diversion work. Good news, but is that a reasonable reflection of the state of affairs in the whole river system? I don
Between me and my husband we've owned more MP3 players over the years than I can count, including Sansas, iRivers, iPods (classic & touch), the Ibiza Rhapsody, etc. But, the last few years I've settled down to one line of players. Why? Because I was happy to discover how well-designed and fun to use the underappreciated (and widely mocked) Zunes are.
Sorry for the morph, Louis. The kids were watching South Park the other night and the topic was transgender operations. It produced the splendid quote from the dissatisfied tranny, to whit, "d'you mean I'm not really a woman, just a guy with tits and a mutilated penis".
Back to the topic, Boxer is spot on with the state of the science.
Louis
I can't comment on your gender status Louis, but if you catch rainwater and boil it away, you'll find a trace of salt left behind. It is oceanic in origin and the saltfall varies according to distance from the ocean. At Broomehill it is probably about 20-30kg/ha per year. 400mm rainfall gives 4,000kl of rain which is 4 million kg of water, so 20kg of salt is about 5ppm (check my decimal places?). And if you measure the amount of salt that falls on a catchment, and compare that to the amount that leaves the catchment in streamflow, in an uncleared catchment, there is a state of dynamic equilibrium. In high rainfall catchments, probably above 800-900mm/yr, there's less salt accumulated because there is always some flushing of the soil profile. Uncleared WA catchments with less than about 500-600mm rainfall have less than 1% of the rainfall emerging as streamflow, with the other 99% accounted for by evapotranspiration. I wonder what the figures are for the Murray Darling?
I've also been told that if you divide the amount of salt stored per ha by the annual saltfall, ta da!!! you get about the period of time since the last ice age (14,000 years?). Take this last bit with as much salt as you wish, but I think it's about right.
Louise?
Eeek no one told me I had an operation lately! Must be all the salt!
Seriously Ian, if that were the case we would also observe a steadily increasing salt increased in our water catchments. Further evaporated water does not carry salt, unless my I have forgotten Chemistry 101. And of course distilled water is water sans the salts.
However I would consider the possibility of continental sized tsunamis washing over continents and leaving their salt as precipitate after the sea soaked the land over which it traversed.
Thank god for declining rainfall in at least parts of Western Australia. In a wetter rather than dryer environment the salt problem might even be worse. Climate change clouds or lack of them may have a non sodic lining.
After a drive through WA wheat belt a few years ago I was impressed by the number of farms with tree plots, they may be small but the action seems to be increasing at an exponential rate if only from a low base.
Louise, my understanding of the WA situation is that each megalitre of rainfall has about 40kg of salt in it courtesy of the Southern Ocean. This is only 40ppm (sea water is 35,000ppm) and undetectable to taste but the accumulation over a few hundred millenia creates a problem. Combine this with mild winter rains on gentle slopes and plains and there is none of the flushing effect that normally reduces the scale of the problem. It is the flushing effect from more intense summer rains that has limited the salinity problem in Queensland and Northern NSW.
Warwick,
time for another Sunday 🙂
Louis
I might comment here, having friends at Broomehill in WA, but what intrigues me, as a geologist, is the source of all this salt.
The bedrock in SW Australia is generally granite.
What regolith process produces all this salt? Where is it coming from?
I know it is there, and that clearing etc, exacerbates it, but so much sodium chloride?
Is the salt part of the Quaternary blanket covering most of the continent? Does this stratigraphic layer host the salt?
Just a few De Bonian thoughts.
The only problem with that option, Rog, is that after infesting the place with their discarded whims and high morality paving positions, they will then decide that it is a farmers 'duty of care' to clean up their mess. And when we attempt to inform them on the inequity of it all it will be a case of, "gosh, look at the time, got to go, catch ya later".
Try getting an article published in the Age, Courier Mail or SMH that sheets home blame to the stupidity of their own readers. Fat chance. They are all legends in their own lunchtime, with a commensurate attention span.