The ocean: key to sustainable water management in a world in crisis

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In a world where climate change, population growth and urbanization strain natural resources, water is a central challenge. Carlos Duarte, Research Professor at KAUST, argues that oceans must be integral to water management. He highlights how terrestrial water flows carry sediments, salts, nutrients and pollutants to the sea, altering salinity, density, circulation and fisheries. A major consequence is eutrophication-driven dead zones caused by excess nitrogen and phosphorus from agriculture and urban runoff. Historical and contemporary examples— from 19th-century sewer expansion to late wastewater treatment in parts of Europe—show how human waste and fertilizer use have long degraded coastal ecosystems. Even positive, unplanned events, such as fertilizer shortages, revealed that reducing nutrient runoff can allow marine recovery.

Duarte examines solutions and trade-offs: desalination supports water-scarce populations but produces brine that can create hypoxic seabed zones unless managed; new uses for brine, such as incorporating it into cement that sequesters CO₂, offer promise. He also stresses climate-driven precipitation extremes that threaten water and food security, and proposes expanding low-water, low-carbon industrial aquaculture and seaweed farming to supplement terrestrial food systems. Duarte calls for an integrated land–sea approach: treating ocean and land water as one cycle to achieve smarter resource use, protect biodiversity and ensure sustainable food and water security.

Carlos Duarte invites us to rethink the role of the oceans in global water management, highlighting innovative solutions to face the climate crisis and ensure a sustainable future for humanity.

In a context where climate change, population growth and urbanization intensify pressure on natural resources, water emerges as one of the most critical issues of our era. Faced with this challenge, the Bankinter Innovation Foundation has convened the think tank Future Trends Forum: The quest for clean waters, bringing together leading experts and leaders in water management.

In this third article in the series, after that of David Sedlak, who proposed three key strategies to face the challenge of water, and that of Yael Glazer , who explained the water-energy nexus, Carlos Duarte invites us to reconsider the importance of the oceans in water management.

Carlos Duarte, Research Professor in Red Sea Ecology at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia, offers an in-depth insight into how water use on land significantly influences the oceans.

If you want to see Carlos Duarte’s presentation, you can do so in this video:

“How does our use of water on land affect the oceans?” #WaterForum

Duarte begins his presentation with a surprising statement: 80% of the water on our planet comes from outer space, a “gift” that arrived on Earth after its initial cooling. Although most of this water is found in the oceans, Duarte notes that the human approach to water management often excludes the oceans’ critical role in the global water cycle.

The interaction between land and ocean

The water that flows from the land into the oceans not only carries fresh water, but also a variety of elements that affect the physical and chemical properties of the ocean. This includes sediments, salts, nutrients, and contaminants. Duarte mentions that the entry of fresh water alters the salinity, density and productivity of the ocean, which has direct implications for ocean circulation and fisheries.

One of the most pernicious effects of human intervention in this cycle is the proliferation of dead zones in the oceans, areas where oxygen is insufficient to sustain marine life. These zones, according to Duarte, are the result of eutrophication, a process caused by excess nutrients (particularly nitrogen and phosphorus) being dumped into the ocean from urban and agricultural areas.

The legacy of pollution and today’s challenges

The problem of ocean pollution is not new. Duarte reminds us that the modern sewer system began in Philadelphia in the late 19th century, a development that radically transformed human waste management, but also introduced large amounts of nutrients and pollutants into coastal waters. However, even today, developed countries such as Belgium continue to have serious wastewater treatment problems. In fact, Brussels did not start treating its wastewater properly until 2010.

Another issue addressed by the expert is the effect of industrial fertilizers. During the Cold War, the disruption of fertilizer supplies from the Soviet Union to several Eastern Bloc countries and Latin America led to a significant improvement in the health of marine ecosystems such as the Black Sea and the Caribbean. This “unplanned experiment” showed that reducing the amount of fertilizer that reaches the ocean can reverse, at least partially, some of the damage caused by eutrophication.

Desalination: A Challenging Solution

Duarte also refers to desalination as a critical solution for water-scarce areas, such as Saudi Arabia, where he lives and works. Desalination has made it possible to sustain a population of 35 million people in a region that would otherwise not be able to support even 10% of that figure. However, desalination presents its own problems, especially the production of brine, a concentrated by-product that, if not properly managed, can severely damage marine ecosystems.

The brine, according to Duarte, can sink to the seabed, blocking the exchange of oxygen and generating hypoxic areas that cause the death of marine organisms. Despite these challenges, the expert sees an opportunity in brine management, presenting a recent innovation: a technology developed by the company Partanna, which uses brine as a main component in cement production, an advance that could significantly reduce the negative impacts of desalination. As an added bonus, this type of cement naturally removes large amounts of CO₂ from the atmosphere during its setting, contributing to Net Zero goals.

Climate change and water insecurity

Another of the central themes of the presentation is how climate change is altering precipitation patterns, which leads to extreme phenomena such as droughts and floods. In Brazil, for example, in less than a year there have been both record lows in the Amazon and widespread flooding. These fluctuations, in addition to affecting water availability, have a devastating impact on food production, which is already under pressure due to growing global demand.

Duarte warns that global food security is at risk unless measures are taken to manage our water resources more intelligently. However, it offers a promising solution: industrial aquaculture. 20% of global food production already comes from aquaculture, a sector that has almost zero water impact and could be expanded to relieve pressure on land-based agricultural systems.

The ocean as a source of solutions

For Carlos Duarte, the key is to integrate the management of water and food resources on land and oceans. He argues that the oceans offer a unique opportunity to produce food sustainably and with a very low carbon footprint. For example, seaweed farming not only has a positive environmental impact, but could also double the planet’s food production capacity if some of the production of terrestrial animal proteins were shifted into the ocean.

A new vision for the future of water

Carlos Duarte closes his presentation with a reflection that invites a paradigm shift. He suggests that it is time to stop seeing water on land and seas as separate entities and start managing them in an integrated way. This “smart” view of water use, which combines land and marine solutions, can help mitigate the effects of climate change and could be key to ensuring food security and preserving biodiversity in the coming decades.

In this third article in the series on The quest for clean waters forum, it is clear that the solution to global water and energy challenges cannot exclude the oceans:

“Water, far from being a problem, is a gift that we must manage wisely to ensure a sustainable future for humanity.”

More articles from the series on The quest for clean waters forum: