The world’s waters are rapidly losing dissolved oxygen, and scientists say this poses one of the greatest threats to Earth’s life-support systems.
Just as oxygen in the air is essential for animals like us, dissolved oxygen (DO) in water is essential for healthy aquatic ecosystems, whether freshwater or marine. Billions of people It is concerning that oxygen in these ecosystems, which depend on ocean and freshwater habitats for food and income, is rapidly and dramatically declining.
A team of scientists has proposed adding aquatic deoxygenation to the list of ‘planetary boundaries’, which outline nine domains that impose limits in their latest form.An environment in which humanity can continue to develop and prosper in the future” .
So far the planetary boundary has been cChange the limit, oocean acidification, sDestruction of the ozone layer, meInterference with the Earth’s nitrogen and phosphorus cycles,ate of biodiversity loss, gLocal freshwater use, lAnd system changes,Aerosol load and cchemical contamination
A team led by Kevin Rose, a freshwater ecologist at Rensselaer Polytechnic Institute in the United States, is concerned that the list overlooks one of the planet’s most important limits.
“The observed deoxygenation of Earth’s freshwater and marine ecosystems represents an additional planetary boundary process,” the authors write. write“It is critical to the integrity of Earth’s ecological and social systems, and to regulating and responding to ongoing changes occurring at other planetary boundary processes.
“The relevant and important oxygen limit is being approached at a rate similar to that of other planetary boundary processes.”
Dissolved oxygen concentrations in water are declining for a number of reasons. For example, warm water cannot hold much dissolved oxygen, and as greenhouse gas emissions continue to warm the air and water temperatures above long-term averages, surface waters are becoming less able to hold this vital element.
Dissolved oxygen may be depleted by aquatic organisms faster than it can be replenished by ecosystem producers. Algal blooms and bacterial blooms, caused by inputs of organic matter and nutrients in the form of agricultural and domestic fertilizers, sewage, and industrial waste, rapidly absorb available dissolved oxygen.
In the worst case, the oxygen is so depleted that the microorganisms suffocate and die, often in larger quantities. Same species as them. Oxygen-independent microbial communities feed on the abundant dead organic matter, and as light diminishes and they grow to densities that limit photosynthesis, they trap entire bodies of water in a vicious cycle of eutrophication.
Underwater deoxygenation is also driven by an increase in the density difference between layers within the water column. This increase may be due to surface waters warming faster than deep waters and ice melting, which reduces ocean surface salinity.
As these layers become more clearly defined, the vertical stratification of aquatic life depends on less movement between the water column layers. These density fluctuations drive the movement of oxygenated surface waters to depth, and without these temperature-driven cargoes, ventilation ceases at lower depths in the aquatic environment.
All of this has wreaked havoc on aquatic ecosystems, many of which our species depends on for food, water, income, and well-being.
The authors of the paper argue that a concerted global effort to monitor and study oxygen depletion in the ‘blue’ parts of the planet is needed, along with policy efforts to prevent rapid oxygen depletion and address related challenges that we already face.
“Reducing greenhouse gas emissions, nutrient runoff, and organic carbon inputs (e.g., raw wastewater loads) could slow or potentially reverse oxygen depletion.” write.
“Extending the Planetary Boundaries Framework to Include Deoxygenation as a Boundary [will help] “To concentrate my efforts.”
This paper was published in Perspective. Natural Ecology and Evolution.
