Diet and food waste are key to tackling oceans’ ‘dead zones’
◆ Excess nitrogen from industrial agriculture represents one of the most pressing pollution issues facing our planet today, write Philip Lymbery and Leticia Carvalho
Ona boat 15 miles off the coast of New Orleans and the Gulf of Mexico was blisteringly hot. All around were oil rigs. Some were huge tangles of scaffolding and metal beams; others resembled small cities. At surface level, the pea-green sea below looked normal. But a few metres beneath the surface, everything changed. The water was far murkier, near zero visibility. Down there coating the bottom half of the water in a suffocating blanket was the dead zone.
The Gulf of Mexico now boasts the world’s second-largest dead zone, or area of oxygen-depleted water, behind only the Baltic Sea. It’s a squalid claim to fame. The zone emerges every year from February to October, stretching from the shores of Louisiana to the upper Texan coast.
This lifeless bottom layer of ocean has made the Gulf synonymous with the term ‘dead zone’ as it loses the oxygen below and drives anything alive toward the surface. It’s a liquid symbol of what happens when efforts to mitigate environmental damage fail. It’s a real-life worst-case scenario, the marine ‘end of days’. According to the US National Oceanic and Atmospheric Administration (NOAA), in 2023 the Gulf dead zone covered approximately 3,058 square miles. That’s almost two million acres of habitat potentially unavailable. Yet the five-year average is larger still: 4,347 square miles, more than twice the size agreed as a management target.
The Gulf dead zone is by no means alone: there are upwards of 40 around the US coast, and the role played by agriculture is increasingly well documented. Worldwide there are now more than 500 dead zones, with the number doubling every ten years. The main culprit? Nitrogen fertiliser. Every year, large amounts of commercial fertiliser containing the ‘Big 3’ primary nutrients: nitrogen, phosphorus and potassium, and manure are applied to soils. Excess nutrients wash into rivers and end up in the sea. In May 2015, some 104,000 metric tons of nitrate and 19,300 metric tons of phosphorus flowed down the Mississippi and Atchafalaya rivers into the Gulf of Mexico. That’s equivalent to a flotilla of more than 4,000 shipping containers heading downriver in just one month, fully loaded with pollution.
Only recently has scientific advancement shown how nitrogen cascades through ecosystems, creating environmental problems. Worldwide, humans create more than 160 million metric tons of nitrogen each year, far more than the environment has had to cope with through the ages. The rise in industrial agriculture has led to a massive spike in pollution from excess nitrogen and other nutrients lost to the environment. Scientists fear that the amount of nitrogen pollution emitted by global animal farming is more than the planet can cope with. Aimable Uwizeye at the UN’S Food and Agriculture Organisation found that animal farming accounts for about a third of all humanity’s nitrogen emissions. Of this, 68 per cent of emissions are attributable to crops grown to feed animals, followed by nitrogen released by the build-up and management of manure.
We’ve known for a long time that using nitrogen as fertiliser is great for increasing productivity but there's a whole range of threats resulting from nitrogen leaking into the environment. By considering nitrogen as a whole, it is becoming increasingly clear that nitrogen pollution represents a massive waste of valuable fertiliser and other nutrient resources.
Nitrogen allows a safe atmosphere in which life can flourish, while avoiding the flammable consequences of too much oxygen. While carbon gives the basic skeleton of organic matter, nitrogen is fundamental to life’s functioning and diversity. However, excess nitrogen in our environment represents one of the most pressing pollution issues facing our planet. Nitrogen pollution contributes to the triple planetary crisis of climate change, nature and biodiversity loss, and pollution and waste. Today, about 80 per cent of reactive nitrogen, estimated to be worth US$200 billion, is lost to the environment every year. Bottom line, nitrogen is now accumulating in the environment faster than our capacity to break it down.
It’s been 20 years since former UNEP executive director, Klaus Toepfer, warned that “humankind is engaged in a gigantic, global, experiment”, not least as a result of the inefficient and often overuse of fertilisers. “What is clear is, that unless urgent action is taken to tackle the sources of the problem, it is likely to escalate rapidly,” he said. As things stand, that urgent action hasn’t happened.
While nitrogen is key to food security, overuse of ammonium-based fertilisers acidifies soil, putting the environment and human health at risk. Therefore, fast action on awareness raising and sciencebased policy is needed. It’s critical that governments accelerate actions and legislation to significantly reduce nitrogen waste globally by 2030 and promote sustainable nitrogen management. This could lead to billions of dollars in savings, while benefiting the environment, biodiversity and human health.
UNEP’S new interactive briefing on beating nitrogen pollution describes nitrogen pollution as “one of the most pressing pollution issues facing humanity, threatening our environment, health, climate and ecosystems”.
What is becoming increasingly clear is that nitrogen pollution, from fertiliser or human or animal waste, should interest anyone who cares about our health, nature, and the future of plant and animal life. To achieve sustainable nitrogen management, we will need to improve the performance of synthetic nitrogen fertilisers, increase the use of organic fertilisers, and boost the recycling of nutrients from agriculture. Moving towards more sustainable diets and dramatically cutting the amount of food we waste could lower the agricultural sector's nitrogen needs.
Philip Lymbery is chief executive of Compassion in World Farming, a former United Nations Food Systems Champion and an award-winning author. Leticia Carvalho is the head of the Marine and Freshwater Branch, United Nations Environment Programme.