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March of the dead zones

By Julian Cribb - posted Friday, 24 August 2012

Out of sight, and largely out of mind, something deeply disturbing is taking place in the world’s oceans and estuaries: hundreds of dead zones, areas devoid of oxygen and the sea life it supports, are forming.

In recent decades the number of these aquatic black spots has risen steadily. At the latest count there were 479 such sites, distributed along the most populous coastlines of Europe, Asia, the Americas and even Australia. Together they cover an area somewhat larger than Victoria.

Dead Zones are not a new phenomenon. The first one was spotted in the 1850s when industrialisation killed the Mersey River in the UK. But since then they have metastasized, steadily and remorselessly invading all the oceans and seas most affected by human activity on land. Like the ominous blotches on a cancer patient’s x-ray, you can see their spread on the world map at:


The cause of Dead Zones is well understood: they are driven by the avalanche of nutrients which humanity dumps in the oceans – from agriculture, sewage, leaky landfills, urban stormwater, soil erosion, industrial and vehicle emissions. This rich nutrient soup provides the food source for vast blooms of algae – and as these die off they sink to the sea floor and decompose causing blooms of bacteria which strip the essential oxygen from the water column, often resulting in fish kills – their most visible impact. They are also hastened by global warming, which stratifies the water, trapping the stagnant water and preventing it from mixing with the oxygen-rich surface layer.

What many people do not realise is that some of the worst extinctions in the history of life on Earth occurred because of a process very similar to this. In the biggest of the lot, the Great Death of the Permian around 252m years ago, an estimated 95 per cent of marine species were wiped out – rugose corals, nautiloids, armoured fish, trilobites – never  to be seen again.

What triggered it is still a scientific mystery – an outbreak of volcanism, striking asteroids, a giant solar storm, colossal seabed methane eruptions: who knows? – but the geological evidence points to a massive global spike in CO2 levels, accompanied by rapid planetary warming, huge outbreaks of anoxia (loss of oxygen from seawater) and the destruction of marine habitats. One thing is fairly clear – by the end of it all fungi and moulds were rulers of the Earth, feasting on the dead.

The multiplying Dead Zones in the world’s oceans today not only resemble the Permian event on a local scale in terms of what drove them – but have two additional drivers: overfishing and pollution from the 83,000 chemicals which humans manufacture on the land and then carelessly liberate into the global environment.

The biggest contributors of all are the 110 million tonnes of nitrogen, 9 million tonnes of phosphorus and other nutrients which we unleash into the planetary ecosystem every year as we try to feed ourselves. That is off-the-scale compared with what the pre-human Earth circulated naturally.

The really unsettling fact is that, if we continue to depend upon agriculture for our food supply, then humanity’s dependence on artificial fertilisers is likely to double by the 2060s – and so will our indiscriminate release of nutrients into the world’s rivers, lakes and oceans. That release, in turn, will spawn more and larger Dead Zones – like that affecting 22,000 square kilometres of sea at the mouth of America’s Mississippi river. In Australia we are not short of warnings, in the form of the Gippsland lakes, WA’s Peel-Harvey inlet, the Hawkesbury and Richmond rivers in NSW, Queensland’s Moreton Bay and a dozen more.


The solution to this unsettling problem is quite simple and even technically feasible: it is to recycle our nutrients. It is to prohibit the discharge of any form of nutrient-enriched waste by any individual, company, government or agency. And it is to mandate the return of all such wastes into the food and fibre producing industries or other productive uses, like carbon plantations or algae farms for food and fuel production.

At present neither Australia, nor indeed most other countries in the world, has a plan to recycle nutrients. Without such a plan, despite the assertions of politicians and their public servants, nations will remain food insecure, exposed to scarcities and price shocks of oil and fertilisers.

Most societies increasingly recycle their glass, their aluminium, their steel, their building materials, their paper, even their water – so why the blind spot with nutrients? It is almost as if we do not understand what keeps us alive, what causes our living planet to function (or dysfunction).We have to be smarter than that.

The recycling of nutrients can not only avert the death of large areas of ocean and freshwater – potentially it can green our cities, feed us and our animals and power all our vehicles, ships and aircraft renewably. It will generate a host of sustainable new industries, interesting high-tech jobs, both urban and rural, and valuable knowledge exports. It will ensure we never need entrust our nation’s future to unreliable foreign imports of oil, fertiliser or food.

By heeding the warning signal provided by the Dead Zones, we can generate great national advantage, self-sufficiency and resilience, show international leadership – and thus help to avoid overstressing the Earth systems on which we all depend. We have a choice: we can either bequeath the planet to our great grandchildren – or to the fungi. Which would you prefer?

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About the Author

Julian Cribb is a science communicator and author of The Coming Famine: the global food crisis and what we can do to avoid it. He is a member of On Line Opinion's Editorial Advisory Board.

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