Deoxygenation On Riverine Ecosystems

Relevance: GS3 - Environmental Pollution & Degradation

(Source: Down to Earth, 09/19/2023)

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Why in the news?

• Recently, a study published in the journal Nature Climate Change, revealed that rivers are warming and losing oxygen faster than oceans.
• The study shows that of nearly 800 rivers, warming occurred in 87% and oxygen loss occurred in 70%.

How was the research conducted?

• The research was led by Pennsylvania State University’s research team, who used artificial intelligence and deep learning approaches to reconstruct historically sparce water quality data from nearly 800 rivers across the U.S. and central Europe.
• It was found that rivers are warming up and deoxygenating faster than oceans, which could have serious implications for aquatic life and the lives of humans.
• To conduct their analysis, the researchers trained a computer model on a vast range of data from annual precipitation rates to soil type to sunlight, for 580 rivers in the United States and 216 rivers in Central Europe.

Findings of the study

• Widespread Deoxygenation: The study found that rivers are experiencing deoxygenation at a rate faster than oceans. Specifically, nearly 70% of the 800 rivers studied in the United States and Central Europe showed oxygen loss.
• Rapid Warming: In addition to deoxygenation, the research revealed that 87% of the rivers studied were experiencing warming. This indicates that river temperatures are rising.
• Urban vs. Rural Differences: Urban rivers exhibited the most rapid warming, while rural rivers showed slower warming but faster deoxygenation. This suggests that human activities and urbanization may play a significant role in these trends.
• Future Projections: The study projected that future deoxygenation rates in these rivers could be between 1.6 and 2.5 times higher than historical rates. This suggests that the problem is likely to worsen in the coming years.
• Immediate Threat to Aquatic Life: Low oxygen levels in rivers pose an acute threat to aquatic species. The study warns that within the next 70 years, certain fish species could face extinction due to prolonged periods of low oxygen.
• Implications for Water Quality and Ecosystems: The findings have significant implications for the quality of river water and the overall health of riverine ecosystems. Deoxygenation can disrupt the balance of aquatic life and ecosystem functioning.
• Challenges in Understanding: The study highlighted that riverine water temperature and dissolved oxygen levels, crucial indicators of water quality and ecosystem health, are poorly understood due to a lack of consistent data and the complexity of variables affecting oxygen levels in watersheds.
• Comparison to Coastal Dead Zones: It draws a parallel between the deoxygenation observed in rivers and the creation of dead zones often seen in coastal areas like the Gulf of Mexico. This implies that some rivers may no longer sustain life as they did in the past.

What are the causes of deoxygenation?

• Eutrophication (Nutrient Run-off and Sewage Pollution): It is a major contributor to deoxygenation in coastal waters. It results from increased nutrient run-off from agricultural activities, sewage discharge, and land pollution.
  • Excessive nutrients, particularly nitrogen and phosphorus, stimulate the growth of algae and phytoplankton.
  • As these organisms die and decompose, oxygen is depleted from the water, leading to "dead zones" with very low oxygen levels.
• Nitrogen Deposition from Fossil Fuel Burning: The burning of fossil fuels releases nitrogen oxides (NOx) into the atmosphere. These nitrogen compounds can be deposited into oceans through atmospheric deposition and runoff.
• Widespread Impacts from Ocean Warming: Ocean warming, driven by climate change, is a significant factor contributing to deoxygenation. As the ocean temperature increases, water holds less dissolved oxygen.
• Acidification and CO2 Emissions: Anthropogenic carbon dioxide (CO2) emissions are a key driver of ocean acidification, which is closely linked to deoxygenation. Elevated CO2 levels reduce the pH of seawater, making it more acidic.

Impact on Marine Life

• Threatening fish species: Low oxygen zones in the ocean can lead to huge fish kills, with thousands of fish washing up dead on the shore. Lower oxygen levels in rivers have also been seen to result in huge masses of fish floating dead on the river surface.
  • For example: Earlier this year, receding flood waters resulted in such low oxygen levels that the Darling River near the Australian town of Menindee became clogged with millions of fish.
• Increase in Greenhouse Gas: Declining oxygen can also lead to increased amounts of greenhouse gases being released from the river and toxic metals being produced.
  • The researchers' model also showed that many species of fish could die out completely as a result of the oxygen loss and warming temperatures in the rivers over the next 70 years.
• Reduced Growth Rate: Marine species may experience slower growth rates due to limited oxygen availability, affecting their development and overall health.

What can be done?

• Reducing Carbon Emissions: One of the primary causes of oxygen loss in the oceans is global warming driven by greenhouse gas emissions, and to slow down and potentially reverse this trend, it's crucial to significantly cut carbon dioxide emissions.
• Mitigating Greenhouse Gas Emissions: Slowing down ocean deoxygenation can be achieved by mitigating greenhouse gas emissions, which will require global efforts to transition to cleaner energy sources and reduce reliance on fossil fuels.
• Addressing Nutrient Pollution: Nutrient runoff from agriculture and sewage effluents contributes to oxygen depletion in coastal waters. To tackle this problem, solutions should be tailored to local needs and economies.
• Protecting Marine Ecosystems: It's essential to better protect marine ecosystems, as this can help conserve marine genetic biodiversity and promote the recovery of ocean life. However, this should be coupled with significant reductions in carbon dioxide emissions to be truly effective.

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FAQs

MCQ

Question: Consider the following statements regarding Ocean deoxygenation:

1. It refers to the loss of oxygen from the oceans.
2. Climate Change and Eutrophication are the two significant causes of loss of oxygen from the oceans.

Which of the statements given above is/are correct?

(a) 1 only

(b) 2 only

(c) Both 1 and 2

(d) Neither 1 nor 2