Cultivated algae can absorb excess nutrients that harm human health and marine life – Science

It’s easy to think that more nutrients – what life needs to grow and thrive – would promote more vibrant ecosystems. Yet nutrient pollution has actually wreaked havoc on marine systems, contributing to harmful algal blooms, poor water quality, and oxygen-poor dead zones.

A team of researchers from UC Santa Barbara has proposed a new strategy to reduce large amounts of nutrients – especially nitrogen and phosphorus – after they have already been released into the environment. In a study published in the journal Maritime policy, the authors argue that the incredible ability of algae to draw nutrients from water could provide an efficient and cost-effective solution. Looking at the Gulf of Mexico in the United States, the team identified more than 63,000 square kilometers suitable for algae aquaculture.

“A key goal of conservation ecology is to understand and maintain the natural balance of ecosystems, as human activity tends to throw things out of balance,” said co-author Darcy Bradley, co-director of the Ocean program and fishing at the University of the Environment. Markets lab. Land-based activities, like industrial-scale agriculture, send a lot of nutrients into waterways where they accumulate and flow into the ocean in greater amounts than they would naturally.

Opportunistic algae and microbes take advantage of the overabundance of nutrients, which fuel massive blooms. This growth can have all kinds of consequences, from the production of biotoxins to the suffocation of habitats in virtual monocultures. And while these algae produce oxygen when they are alive, they die so suddenly and in such volume that their rapid decomposition consumes all the oxygen available in the water, turning huge swathes of the ocean into so-called “dead zones”.

Cultivated algae could reduce available nutrients, say the authors, limiting resources for uncontrolled growth of algae and harmful microbes. Algae also produce oxygen, which may reduce the development of hypoxic dead zones.

The authors analyzed data from the Gulf of Mexico to the United States, which they believe illustrates the challenges associated with nutrient pollution. More than 800 watersheds in 32 states provide nutrients to the Gulf, which has led to a growing low oxygen dead zone. In 2019, this dead zone stretched over just over 18,000 square kilometers, slightly smaller than the area of ​​New Jersey.

Grouchy Cortez fish swim under a bloom of “red tide” algae near the Bat Islands in Santa Rosa National Park, Costa Rica. Grouchy Cortez fish swim under a bloom of “red tide” algae near the Bat Islands in Santa Rosa National Park, Costa Rica. Flowers like these can release biotoxins and create oxygen-poor dead zones in the ocean.

Using oceanographic and open-source human use data, the team identified areas of the Gulf suitable for growing algae. They found that about 9% of the U.S. Exclusive Economic Zone in the Gulf could support algae aquaculture, especially off the west coast of Florida.

“Growing algae in less than 1% of the Gulf of Mexico in the United States could potentially meet the country’s pollution reduction targets that for decades have been elusive,” said lead author. Phoebe Racine, a Ph.D. candidate in the Bren School of Environmental Science & Management at UCSB.

“Dealing with nutrient pollution is difficult and expensive,” added Bradley. The United States alone spends over $ 27 billion annually on wastewater treatment.

Many areas are using water quality trading programs to deal with this problem. In these cap-and-trade systems, regulators set a limit on the amount of pollutant that can be released, and then entities trade credits in a marketplace. Water quality exchange programs exist all over the United States, although they are often small, bespoke, and may be ephemeral. That said, they are very promising and, according to Racine, enjoy bipartisan support.

Algae aquaculture would fit perfectly into these initiatives. “Depending on the costs and efficiency of agriculture, algae aquaculture could be funded through commercial water quality markets for anywhere between $ 2 and $ 70 per kilogram of nitrogen removed. “Racine said,” which is within the range of credit prices seen in existing markets. “

In addition, the researchers note that the demand for seaweed is increasing in the food and industrial sectors. Potential products include biofuels, fertilizers and food, depending on the quality of the water, Racine said. This means that unlike many remediation strategies, algae aquaculture could be profitable or even generate income.

And the time seems to have come for the authors’ proposal. “The United States has traditionally had a lot of barriers to doing ocean aquaculture,” Bradley explained. “But there is growing political support in the form of bills and a signed executive order that could catalyze the expansion of the US aquaculture industry.”

This study is the first in a series to emerge from the Algae Working Group, an interdisciplinary group of researchers seeking to understand and map the potential benefits of algae aquaculture to society. They are currently studying a range of other ecosystem services that growing algae could provide, such as benefits to surrounding fisheries and carbon capture. Researchers are also working on an article that explores nationwide nitrogen and phosphorus removal with fine-scale analysis modeling nutrient removal from native algae off the coast of Florida.

As long as humans keep adding nutrients to the environment, nature will find ways to use them. By deliberately cultivating algae, we can grow algae that we know to be benign, useful, or even potentially useful, rather than the opportunistic algae that currently derive these excess nutrients.

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