We often think of nature as being in a fine balance, with scales that cannot be tipped too dramatically either way. Too much of one thing and we risk plummeting the Earth into an ice age, too much of another and we tip into a blazing inferno. We envision a stable equilibrium with conditions that must be maintained to avoid total chaos. Though this was once thought to be the case - when a particularly hot summer might permanently dry up mighty river beds forever - it is actually a false but enduring notion.
The reality is quite the opposite. Nature, biodiversity, ecology, life - all are more dynamic, robust and versatile than we realise. If it wasn’t, anthropogenic behaviour would have destroyed so much more of it by now. Having said that, while Earth can deal with a lot more than we give it credit for, that doesn’t mean we’re not giving it too much to deal with right now. Small changes (emphasis on small) are quite harmless to the natural world. However, our failure to reduce the rate of carbon released into the atmosphere from the burning of fossil fuels, destructive deforestation, and extractive consumer habits are creating a strain on the planet and causing a lasting impact. It is these increasingly rapid and extreme shifts that are putting immense pressure on small biodiverse interactions, leaving our dynamic world unable to keep up.
Change is constant in the natural world and Earth is more than capable of adapting when given the chance but right now we aren’t giving it that chance, or the time. One such example of this instability is the materialisation of dead zones in lakes, rivers and oceans.
The clue is in the name. Dead zones are bad news for the waterways they infiltrate. From those floating at the surface to those kicking back on the seabed, dead zones are uninhabitable for any living organism.
What is a dead zone?
Though there are several different origins of a dead zone, all lead to the same issue - a depletion of oxygen in the water. Low oxygen, or hypoxic, areas are better known as dead zones because little to no oxygen is available for any organisms hoping to live there. Marine life cannot be supported in these conditions so they either die or if possible, leave - creating biologically barren wastelands.
No body of water is safe from the clutches of hypoxia but coastal areas and lakes are more vulnerable than elsewhere. So far, 415 dead zones have been identified worldwide with a notably steep increase in the last 50 years. The third largest dead zone in the world, known as the Gulf Dead Zone, is located in the northern Gulf of Mexico and covers over 20,000 square kilometres.
The largest1 is up for debate but can be found either in the Black Sea or the Arabian Sea. The Arabian Sea dead zone covers almost the entire 63,700 square-mile Gulf of Oman and is caused by warming waters (human-made) which are more buoyant and so unable to sink and ventilate the already Oxygen Minimum Zone (OMZ) 200-300 metres below.
The other largest dead zone in the world is in the Black Sea. This one is naturally occuring - which may explain why sources disagree on which is the largest . Encompassing the lower portion of the Black Sea, this dead zone stands apart from the entire upper portion of the water which is mixed with the Mediterranean Sea and thus oxygenated.
The same, yet different. What causes these dead zones is what sets them apart. An unfortunate example of our all too human footprint.
What causes dead zones?
Dead zones can be formed in a number of different ways but the results are always the same. Uninhabitable. Desolate. Dead.
The most common cause is eutrophication. Strangely enough, this begins with a large increase of nutrients in the water, particularly phosphorus and nitrogen. These lead to an imbalance - manageable if minimal but lethal if the body of water becomes overwhelmed by these nutrients. In healthy quantities, these nutrients feed the growth of blue-green algae with no issues. However, as the nutrients concentrate too thickly the algae grows out of control and blooms becoming harmful for the rest of the environment. Forming a thick layer at the surface, life beneath the water is suffocated without access to sunlight or oxygen. To make things worse, when the dense growth of algae eventually dies it will sink and decompose in the water consuming oxygen as it goes. This can last for days, months or long enough to cause major fish die-offs and mark the area an official dead zone. Not great for the fishies whichever way you look at it… Cyanobacteria is also harmful to humans as toxins produced by the bacteria can damage the liver, central nervous and renal system, and the gastrointestinal tract. In other words, it’s poison.
Due to human activity, the concentration of nitrogen has reached double the usual level, while phosphorus has tripled. This led to a proliferation of dead zones across the world. Sources of excess nutrients in waterways most often include; runoff from industrial areas, agricultural manure, sewage, storm water and lawn fertiliser.
In the exact same way, ‘red tides’ are caused by Karenia brevis - another type of algae, and fun fact: not always red. Though these usually occur only in saltwater environments, they are equally harmful to the ecosystem. In some areas of the world, overly nutrient-rich waters attract plankton which then bloom to such an extent that they too create a dead zone.
What can be done?
As the formation of a dead zone means all life in the water has already been destroyed, adaptation is not an option. The key to reducing the scale and number of them in our waterways is to turn off the tap of excess nutrients. Just as quickly and severely as dead zones emerge, life can bounce back to oxygenated, healthy ecosystems.
Some have suggested setting a daily maximum limit of nutrient flow, to allow some leakage but not enough to impact oxygen levels or the health of the aquatic species. But do we really want to settle for natural bodies of water which contain contaminants potentially damaging to our health, and with unknown consequences to the rest of the life these waters harbour?
Regulation around sewage facilities and their waste disposal schemes need to be improved. We need to stop untreated waste pouring into natural bodies of water. These should be both swimmable and drinkable. Fertilisers used in agriculture usually run off the land after heavy rainfall, draining to rivers and eventually into our oceans. Upscaling natural fertilisers at a global level (as opposed to the dangerous chemicals we currently use) would mean reduced consequences when runoff does occur. Coming in at all angles, atmospheric sources of nitrogen are a risk to our water cycle too as our reliance on fossil fuels and chemical fertilisers release nitrogen into the atmosphere which falls back to the earth as rain or snow. How do we stop that without ending our dependence on fossil fuels and switching to renewable energy?
The mitigation methods are clear, if not easy to implement. The extreme shifts we’re inflicting on the natural world, like the ones that create dead zones, spell trouble. It’s not a slight imbalance that the Earth is struggling to deal with, rather the velocity of change.
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Amie 🐋
No one seems to agree on this.
Thank you for another important post! You might enjoy George Monbiot’s “Regenesis: Feeding the World Without Devouring the Planet” for both a deep exploration of the role agriculture plays in these dead zones and other kinds of pollution, and possible solutions!