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Excess nutrients are creating ocean dead zones

In a stark announcement, researchers from the Royal Netherlands Institute for Sea Research (NIOZ) have sounded the alarm on an escalating problem in our oceans — the growth of “dead zones.” These regions of critically low oxygen create marine ecosystems unable to support most forms of life.

Recent study reveals that a major culprit driving dead zone expansion is a worrying trend: excess nutrients entering the ocean.

What are ocean dead zones?

Ocean dead zones are areas in the ocean where the oxygen levels are so low that most marine life cannot survive. These zones are also known as hypoxic areas.

Oxygen is essential for the survival of fish, shellfish, and other marine organisms. Without enough oxygen, these creatures either die, move to other areas, or face significant reproductive and health issues.

The size and number of oceanic dead zones have been increasing globally, posing a significant threat to marine ecosystems.

These areas can have devastating effects on marine biodiversity and fisheries, impacting food security and economies dependent on marine resources.

Reducing nutrient pollution from agriculture, wastewater treatment, and other sources is critical to addressing the expansion of dead zones.

Excess nutrients and ocean dead zones

Zoe van Kemenade, a researcher at NIOZ, and her team have been peering into the ocean’s past off the coast of California. They found that while climate change contributes to the problem, a much more sinister force is at work: excess nutrients.

But wait, aren’t nutrients good? Well, in moderation. Our overuse of fertilizers in agriculture, along with pollutants from sewage, create a nutrient overload that flows into rivers and eventually to the sea. In the water, it’s like a giant buffet for algae.

This leads to massive algae blooms, but when these huge clumps of algae die, bacteria feast on them. This decaying process gobbles up oxygen, leaving a suffocating wasteland behind.

Signs of the absence of life

At the heart of this investigation are ladderanes, intriguing molecules that serve as telltale signs of ancient life – or rather, the absence of it in the traditional sense. These molecules are the fingerprints left by anammox bacteria, a group of microorganisms that flourish in environments devoid of oxygen.

Zoë van Kemenade’s research brings these microscopic detectives into the spotlight. Anammox bacteria are unique because they can survive and thrive in completely oxygen-free zones by performing a process known as anaerobic ammonium oxidation.

During this process, they produce ladderanes, molecules characterized by their ladder-like structure, which are essential for protecting the bacteria from harmful metabolites produced during their metabolic activities.

History of oceanic dead zones

The discovery of ladderanes in seabed samples is a significant indicator of past oceanic conditions. These molecules are evidence of environmental conditions that once pervaded the Earth’s oceans.

The presence of ladderanes in ancient sediment layers points to periods when parts of the ocean were so devoid of oxygen that only specialized life forms like anammox bacteria could exist.

By analyzing these molecules, scientists can piece together a history of the ocean’s oxygen levels such as how and when these dead zones occurred.

This provides a crucial understanding of the impact of factors contributing to the current expansion of oceanic dead zones.

Through the lens of ladderanes, we gain a clearer view of the ocean’s ancient mysteries. The revelations illuminate a critical and somewhat counterintuitive aspect of marine science. One might intuitively assume that ice ages would make oceans less susceptible to oxygen depletion.

However, Van Kemenade’s findings shatter this assumption. They reveal a complex interplay between temperature, nutrient levels, and marine oxygen content that defies simple predictions.

Study significance

This discovery underscores a vital point: while temperature plays a role in ocean oxygen levels, an abundance of nutrients in the water can be an even more potent driver of these devastating dead zones.

Nutrients, often stemming from land-based runoff containing nitrogen and phosphorus, fuel explosive blooms of algae.

As these algae die and sink to the ocean depths, their bacterial decomposition becomes an oxygen-hungry process, ultimately creating the hypoxic or anoxic conditions that define a dead zone.

The implications of Van Kemenade’s findings are weighty, especially in the context of our modern oceans. The chilling fact that our oceans hold two percent less oxygen than just fifty years ago highlights the urgency of this issue.

This decline isn’t a mere historical footnote; it’s a crisis unfolding before our eyes, with potentially disastrous consequences for marine ecosystems and the biodiversity they harbor.

What can we do about the ocean dead zones?

Right now, the massive amounts of nutrients we’re dumping into the oceans are supercharging dead zones. But the good news? This is a problem we have the power to fix, at least in part.

“Extra nutrients in the water can cause major problems for ocean biodiversity. Oxygen-less conditions can have major consequences for the ecosystem, but also for fisheries, for example,” said Van Kemenade.

Choose sustainable

One actionable step is to support agriculture that prioritizes the health of the ecosystem. By choosing products from farmers who engage in organic or regenerative farming practices, consumers can play a role in reducing the amount of fertilizer runoff that enters our waterways.

These practices not only minimize nutrient pollution but also enhance soil health, carbon sequestration, and water retention.

Upcycled beauty

Personal care products are another unexpected source of nutrient pollution. Many of these products contain ingredients that, when washed down the drain, contribute to the nutrient load in water bodies.

Opting for eco-friendly alternatives that are biodegradable and free from harmful additives can significantly reduce this impact.

Get involved

Civic engagement is crucial in advocating for healthier oceans. Supporting organizations dedicated to protecting waterways, promoting sustainable practices, and lobbying for stricter regulations on polluters can amplify efforts to tackle this issue.

Collective action and pressure can lead to the implementation of policies that better manage agricultural runoff, wastewater treatment, and industrial discharges.

It’s a daunting challenge, but as this research makes crystal clear, the fate of the oceans – and our own well-being – depends on it.

The study is published in the journal Biogeosciences.


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