The serene flow of a river has long been a symbol of life, endurance, and cultural heritage, particularly in the tropical landscape of Sri Lanka. From the majestic Mahaweli to the industrious Kelani, these waterways have sustained civilisations for millennia. However, a silent and invisible crisis is unfolding beneath the surface. Recent scientific research has highlighted a precarious trend: the world’s rivers are losing their breath. Climate change is systematically reducing the levels of dissolved oxygen in freshwater systems, a phenomenon known as deoxygenation, which threatens to dismantle aquatic ecosystems and the human livelihoods that depend upon them.
The Scientific Revelation: A Global Decline
A comprehensive study conducted by environmental scientists at the Chinese Academy of Sciences, led by researcher Wei Guan, has utilised satellite data and advanced artificial intelligence to track oxygen levels in more than 2,000 rivers across the globe since 1984. The findings, published recently in the journal Science Advances, are sobering. The analysis reveals that oxygen levels in global rivers have dropped by an average of 2.1% over the past four decades.
While a two percent decline might appear marginal to the casual observer, in the delicate balance of aquatic chemistry, it represents a significant shift toward instability. Dissolved oxygen is the lifeblood of a river; it is essential for the survival of fish, invertebrates, and the aerobic bacteria that decompose organic matter. When these levels fall, the very foundation of the river’s health begins to crumble.
The study further projects that if the current rate of warming and carbon emissions continues, the world’s rivers could lose an additional 4% to 5% of their oxygen by the end of this century. In certain “hotspots,” including parts of India and the tropical belt where Sri Lanka is situated, the loss could be even more pronounced, potentially leading to the creation of “dead zones” where aquatic life simply cannot survive.
The Mechanics of Suffocation: Why Warming Matters
The relationship between temperature and oxygen is governed by fundamental principles of physics and chemistry. Simply put, warmer water has a lower capacity to hold dissolved gases. As global air temperatures rise due to human-induced climate change, river waters also warm. This warming reduces the solubility of oxygen, causing it to be released back into the atmosphere rather than remaining available for aquatic organisms.
According to the research, nearly 63% of the observed decline in oxygen is directly attributable to this decrease in solubility caused by warming. Furthermore, higher temperatures accelerate the metabolic rates of microbes and other organisms within the water. This increased biological activity consumes oxygen more rapidly, creating a “double squeeze” on the ecosystem: there is less oxygen available, and it is being used up faster than ever before.
Heatwaves, which are becoming more frequent and intense in tropical regions like Sri Lanka, are particularly destructive. The study found that heatwaves alone account for approximately 22.7% of global deoxygenation, significantly spiking the rate of oxygen loss during extreme weather events.
The Sri Lankan Context: Vulnerability of the Mahaweli and Kelani
For the Sri Lankan community, these global findings are not merely academic; they represent a direct threat to the island’s natural resources. Sri Lanka’s rivers are located within the 20°S to 20°N tropical band, which the study identifies as the region hardest hit by deoxygenation.
The Kelani River, which serves as a vital source of water for the capital city of Colombo and numerous industries, is already under immense pressure from urbanisation and industrial runoff. Recent local studies (2003–2023) have indicated a strong correlation between rising temperatures and Biochemical Oxygen Demand (BOD) in the Kelani. As the water warms, the organic pollutants in the river decompose more rapidly, stripping the water of its remaining oxygen. This makes the lower reaches of the Kelani especially susceptible to hypoxic conditions, where oxygen levels fall below the critical threshold of 5 mg/L.
In the case of the Mahaweli River, the island’s longest and most culturally significant waterway, the challenges are compounded by its extensive system of dams and reservoirs. While these structures are essential for hydropower and irrigation, they can also lead to water stratification. In deep reservoirs, warmer, oxygen-rich water stays at the surface while the deeper layers become stagnant and depleted of oxygen. As climate change alters rainfall patterns and increases evaporation, the management of these regulated flows becomes a delicate balancing act to ensure that downstream ecosystems do not suffocate.
Impact on Fisheries and Community Livelihoods
The decline in dissolved oxygen has profound implications for the inland fisheries that are central to the food security and economy of many Sri Lankan villages. Most freshwater fish species require a minimum oxygen level of 5 mg/L to thrive. When levels drop below this, fish experience severe physiological stress, leading to reduced growth, impaired reproduction, and, in extreme cases, mass mortality events.
Furthermore, chronic deoxygenation often leads to a shift in species composition. Sensitive, high-value native fish species may be replaced by hardier, more tolerant species that are often of lower commercial value. For the small-scale fishers along the Mahaweli or the reservoirs of the North Central Province, this means smaller catches and lower incomes.
The impact extends beyond the economy to the very dinner tables of Sri Lankan households. Inland fish are a primary and affordable source of animal protein and essential micronutrients for rural communities. A decline in these fisheries exacerbates food insecurity and increases the vulnerability of families who have limited alternative livelihoods.
A Call for Integrated Management and Adaptation
Addressing the “breathless waters” of our rivers requires a multi-faceted approach. While global efforts to curb carbon emissions are paramount, local adaptation and management are equally critical.
- Integrated Watershed Management: As highlighted by the pressures on the Kelani River, controlling land-use and organic pollution is essential. Improved wastewater treatment for industries and municipalities will reduce the biological demand for oxygen, giving the river a better chance to cope with rising temperatures.
- Monitoring and Early Warning: Establishing systematic monitoring of water temperature and dissolved oxygen levels in the Mahaweli and Kelani basins is a priority. Early-warning systems can alert fishing communities to impending hypoxic events, allowing them to adjust their activities and mitigate losses.
- Restoring Riparian Buffers: Planting trees and maintaining natural vegetation along riverbanks provides shade, which can help keep water temperatures lower and filter out nutrient-laden runoff from agricultural lands.
- Strategic Dam Operations: In regulated systems like the Mahaweli, adjusting dam operations to ensure sufficient environmental flows, especially during dry seasons and heatwaves, can help maintain the necessary aeration for downstream aquatic life.
The Role of eLanka in Connecting the Community
At eLanka, we understand that our heritage is deeply tied to the land and waters of our motherland. Since 2005, we have served as a bridge for the Sri Lankan community worldwide, sharing stories of our culture, our achievements, and the challenges we face. Protecting our environment is a collective responsibility that requires awareness and action.
By staying informed about the impacts of climate change on our precious rivers, we can better support initiatives that safeguard Sri Lanka’s natural beauty and economic stability. We encourage our members and well-wishers to engage with local conservation efforts and to share their stories of environmental stewardship through our platform.
Whether you are in Australia, the UK, or Sri Lanka, the health of the Mahaweli and Kelani affects us all. Together, we can advocate for the protection of these life-giving waters, ensuring they remain vibrant and oxygen-rich for generations to come.
This article was written based on the source https://www.pinalcentral.com/world_news/scientists-find-climate-change-is-reducing-oxygen-in-rivers-worldwide/article_a9aaa0ce-00c5-5f23-a068-7ea33f5739ed.html, kindly email us at info@eLanka.com.au if any information needs to be corrected.
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