The rapid decline in dissolved oxygen (DO) in bodies of water worldwide is emerging as one of the most critical threats to Earth’s ecosystems. Scientists are urging the inclusion of aquatic deoxygenation in the planetary boundaries framework, which defines thresholds crucial for sustaining life and maintaining Earth’s stability.
VITAL FOR AQUATIC LIFE
Dissolved oxygen in water is as essential for aquatic life as atmospheric oxygen is for terrestrial animals. Healthy freshwater and marine ecosystems rely on adequate levels of DO to support diverse species, from microscopic organisms to large fish. The depletion of this oxygen is a significant concern given the billions of people who depend on these ecosystems for food, water, and economic resources.
FACTORS CONTRIBUTING TO DEOXYGENATION
Impact of Global Warming
Warmer water temperatures reduce the capacity of water to hold dissolved oxygen. As greenhouse gas emissions continue to increase global temperatures, both air and water temperatures rise, exacerbating the decline in DO levels. This phenomenon threatens the balance of aquatic ecosystems.
Nutrient Pollution and Eutrophication
Excessive nutrients from agricultural runoff, sewage, and industrial waste lead to algal blooms and bacterial growth, which deplete DO levels. When these organisms die, their decomposition further consumes oxygen, often leading to dead zones where most marine life cannot survive. This process, known as eutrophication, creates a vicious cycle of degradation in aquatic environments.
Stratification and Reduced Oxygen Exchange
The warming of surface waters compared to deeper layers and the melting of ice reduce the movement between these layers. This stratification impairs the natural circulation of oxygen-rich surface waters into deeper zones, further diminishing oxygen availability in lower aquatic layers.
PROPOSAL FOR INCLUDING DEOXYGENATION IN PLANETARY BOUNDARIES
A Critical Oversight
Currently, the planetary boundaries framework includes nine critical processes, such as climate change, ocean acidification, and biodiversity loss. Freshwater ecologist Kevin Rose and his team argue that aquatic deoxygenation is equally crucial and needs to be recognized as a separate boundary to reflect its impact on global ecological and social systems.
Observed Rates and Thresholds
The rates at which oxygen levels are declining in both freshwater and marine environments are comparable to other planetary boundary processes. Recognizing deoxygenation as a boundary would help prioritize research and policy efforts to mitigate this issue.
RECOMMENDED ACTIONS
Global Monitoring and Research
There is an urgent need for global monitoring and research to understand the extent and impacts of deoxygenation. Enhanced data collection and analysis will provide critical insights into the effectiveness of mitigation strategies and the state of aquatic health.
Policy Interventions
To combat deoxygenation, the authors recommend:
- Reducing Greenhouse Gas Emissions: Mitigate temperature increases that contribute to lower oxygen levels.
- Controlling Nutrient Runoff: Implement practices to minimize agricultural and domestic nutrient inputs into water bodies.
- Managing Organic Carbon Inputs: Address raw sewage and other sources of organic pollution.
EXPANDING THE PLANETARY BOUNDARIES FRAMEWORK
Incorporating aquatic deoxygenation into the planetary boundaries framework will help focus global efforts on this critical issue. By acknowledging its significance, policymakers and researchers can better address the challenges posed by declining DO levels.
