Earth’s Water is Rapidly Losing Oxygen, Creating a Major Threat

The levels of dissolved oxygen in the world’s water bodies are dropping quickly, and scientists consider this a major threat to Earth’s life support system.

Much like atmospheric oxygen is crucial for animals, dissolved oxygen (DO) is key for the health of aquatic ecosystems, whether in freshwater or marine environments. Given that billions of people depend on these habitats for food and income, it’s worrying that the oxygen in these ecosystems is decreasing significantly and rapidly.

Proposing Aquatic Deoxygenation as a New Planetary Boundary

A group of scientists is urging the inclusion of aquatic deoxygenation in the list of ‘planetary boundaries.’ These boundaries outline nine essential areas that set the limits within which humanity can sustainably thrive and flourish for future generations.

Currently, the planetary boundaries include climate change, ocean acidification, depletion of the stratospheric ozone layer, disruptions to global phosphorus and nitrogen cycles, loss of biodiversity, global freshwater usage, land-system changes, aerosol pollution, and chemical contamination.

Freshwater Ecologist Kevin Rose Advocates for Inclusion of Aquatic Deoxygenation in Planetary Boundaries

A group led by freshwater ecologist Kevin Rose from Rensselaer Polytechnic Institute in the US worries that this list neglects a crucial aspect of Earth’s limits.

“The authors argue that we should recognize the ongoing deoxygenation of Earth’s freshwater and marine systems as an additional planetary boundary process. This phenomenon is crucial to the well-being of Earth’s ecological and social systems, as it both impacts and is impacted by other planetary boundary processes.”

“Critical oxygen levels are being approached at rates similar to other planetary boundary processes.”

Dissolved oxygen in water decreases for various reasons. For example, warmer waters can’t hold as much oxygen, and as greenhouse gas emissions continue to raise air and water temperatures above their long-term averages, surface waters are losing their ability to retain this essential element.

Additionally, aquatic life can deplete dissolved oxygen faster than producers in the ecosystem can replenish it. Algal and bacterial blooms, stimulated by an influx of organic matter and nutrients from agricultural and domestic fertilizers, sewage, and industrial waste, rapidly consume available oxygen.

In severe cases, oxygen levels drop so low that microbes suffocate and die, often leading to the death of larger species as well. Microbes that don’t need oxygen then proliferate on the decaying organic material, reducing light penetration and limiting photosynthesis, trapping the entire water body in a destructive cycle known as eutrophication.

Warming Surface Waters and Melting Ice Intensify Aquatic Deoxygenation by Increasing Density Differences

Aquatic deoxygenation is also exacerbated by increasing density differences between water layers. This is due to surface waters warming faster than deeper waters and melting ice lowering surface salinity in the oceans.

The more pronounced the layers in the water column, the less mixing occurs between them, which is crucial for underwater life that depends on these vertical exchanges. These density gradients facilitate the movement of oxygen-rich surface water into deeper layers, and without this temperature-driven circulation, ventilation in the lower depths of aquatic environments stops.

These changes have severely impacted aquatic ecosystems, many of which are vital to human food, water, income, and overall well-being.

The authors of the paper advocate for a global effort to monitor and study the deoxygenation of Earth’s aquatic environments, as well as policy measures to prevent rapid deoxygenation and the related challenges we’re starting to encounter.

They suggest that “reducing greenhouse gas emissions, nutrient runoff, and organic carbon inputs (such as untreated sewage) could slow down or even reverse deoxygenation.”

Including deoxygenation in the planetary boundaries framework, they argue, would help direct these efforts more effectively.

Read the original article on: Science Alert

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