Every now and again Sydney gets a dust storm.
Red dirt descends on the harbour city leaving a stain on all exposed surfaces and forces asthma suffers indoors. The cloud usually passes within a few hours on the strong westerlies that brought the problem with them.
The typical conditions that bring this occasional event are simple enough: drought in the centre of the continent and a deep low tracking through the Tasman sea. Winds whip up topsoil and keep it aloft long enough for it to travel far and wide, sometimes even to New Zealand.
Dust storms like this are not common in Sydney. There is a major one every few years that creates a temporary nuisance. After a day it is forgotten and the next rain shower removes the evidence.
Severe thunderstorms, floods and bushfires along with their smoke are the more familiar of nature’s challenges.
However, suppose that the dust storm deposits 0.1 mm of dust across Sydney. Just a thin film of silty redness; nothing that the rain cannot wash away.
Suppose further that this happens at least once every 4 years.
In the lifetime of the current crop of university students, some 0.5 mm has landed and washed away. Not much to write home about — although most university students live at home these days so could just shout to their mums in the kitchen
Since the time past when shiploads of convicts founded Sydney and began to spread out into the hinterlands, these irregular storms have deposited 5.75 mm of dust or a little under a quarter of an inch.
Again not much, but you could scrape it together into piles and make enough soil to sprout some bamboo shoots.
Now assuming the same rates and amounts occurred since the first humans reached Australia, say a minimum of 60,000 years ago by most genetic estimates, then we are looking at around 150 cm of deposited dust, roughly 4 feet 11 inches of the stuff, more than enough to grow things in.
In fact, 4 feet 11 inches is the average height of a modern 12-year-old kid.
What this should tell you is that wind erosion is serious business.
Wind can move soil from a source area and deposit it somewhere else. It can do this very quickly, well within the time bounds of human societies. Give it a bit longer and it can shape landscapes.
If the paddocks in the west of NSW are bare when the pressure discrepancy hits then the wind does its thing even faster. Soil and nutrient exit stage left.
If this is alarming to you it should be.
At a time when we need every gram of nutrient to stay on the paddocks to nurture the plants that we want to eat, it is continuing to blow away on the wind.
Also, know that wind erosion is a perfectly natural process. It has contributed to the flattening of mountain ranges on earth for millions of years. It is not something humans can stop as, despite our biblical edicts of dominion, we can’t stop drought and we can’t prevent air pressure systems from moving around the planet.
We can be smart though and reduce the effects of wind through management. This is a very simple principle — keep groundcover.
That is, don’t leave bare soil anywhere.
Easy to say, not so easy to do. If your livestock are starving under drought conditions and need to eat whatever is left on the paddock there is a strong temptation to let them. Keeping plant cover on the ground requires advanced planning for the dry times so that the livestock are elsewhere or fed from other sources.
Again, really easy to say — especially by a blogger from the city — really hard to do on the farm.
A kicker
In old, already heavily eroded soils like those over much of the Australian inland, the last thing you need to happen is topsoil loss.
Old soils tend to have fewer primary minerals especially k-feldspars (orthoclase, sanidine, and microcline) and micas (muscovite, glauconite and illite). These minerals are called active because they have a high capacity to hold onto and exchange nutrients with plant roots.
Primary minerals act as an important reservoir for potassium (K), with over 90% of K in soils existing in the structure of these minerals. Significant amounts of calcium (Ca), sodium (Na), and silica (Si) and smaller amounts of copper (Cu) and manganese (Mn) are also present in the feldspars. Micas and illite are the most important source of K in many soils, and they also contain magnesium (Mg), iron (Fe), Ca, Na, Si, and a number of micronutrients
This makes growing plants in older soils a challenge as the nutrients exchange is far less than it is in younger soils.
Another kicker
I am writing this update in late January 2020.
It has been an apocalyptic summer on the east coast of Australia. More than 11 million hectares of bushland has burnt, temperature records have been smashed — where I live the daily maximum recorded temperature for December was exceeded by over half a degree Celcius and then in January by a full degree, it was 16.5 degrees above the long term average that day.
Combine the heat with the smoke and even the healthy are calling it. Then the dust storm, a big one. When it passed through Orange in the centre of the NSW it turned day into night and was the worst anyone could remember.
Then the rain came, briefly and yet with such ferocity the lightning strikes took your eardrums out.
This is climate change, my dear readers. All of these severe weather stories are the consequence of more energy in the atmosphere, even the deep chill last winter in the US that the POTUS joked about.
Again we can’t ‘fix’ climate change but we sure as hell should be doing everything we can to mitigate against it.
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Alloporus 