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Giant kelp (Macrocystis pyrifera) holds promise as a potential biofuel and energy crop. paule858/Getty ImagesGiant kelp, the largest species of marine algae on Earth, presents an exciting possibility for biofuel production. A recent study explored a groundbreaking method for cultivating kelp that could allow for large-scale, continuous production. The central concept involves moving kelp stalks daily between sunlit surface waters and nutrient-rich deeper waters.
Unlike traditional energy crops like corn and soybeans, kelp cultivation requires no land, fresh water, or fertilizers. Under optimal conditions, giant kelp can grow over a foot per day.
Kelp generally thrives in shallow coastal waters where both sunlight and nutrients are abundant. However, the challenge lies in the fact that the ocean's sunlit zone reaches only about 665 feet (200 meters) below the surface, and this area often lacks the nutrients necessary for kelp growth.
A significant portion of the open ocean's surface remains nutrient-deficient year-round. In coastal regions, the process of upwelling, where deep waters rise to the surface bringing nutrients, occurs seasonally. Deeper waters are nutrient-rich but lack sunlight.
Our research showed that kelp thrived despite daily variations in water pressure as we moved it between depths of 30 feet (9 meters) and 262 feet (80 meters). This cultivated kelp absorbed enough nutrients from the deeper, darker waters to grow four times faster than kelp transplanted to its native coastal habitat.
Why It Matters
Producing biofuels from land-based crops like corn and soybeans often competes with other land uses and the demand for fresh water. By using plants from the ocean, biofuel production can be more sustainable, efficient, and scalable.
Marine biomass can be converted into various energy forms, including ethanol, which could replace the corn-based additive currently mixed into gasoline in the U.S. Perhaps the most promising end product is bio-crude — oil extracted from organic matter. This bio-crude is made through a process called hydrothermal liquefaction, where temperature and pressure are used to transform materials like algae into oil.
These oils can be refined in existing facilities to create biofuels for trucks and airplanes. Running these long-distance vehicles on electricity isn't feasible yet, as it would require massive batteries.
According to our calculations, producing enough kelp to fuel the entire U.S. transportation system would only require a small portion of the U.S. Exclusive Economic Zone — the ocean territory extending 200 nautical miles from the shore.
A diver is seen here working at the 'kelp elevator.'
Maurice Roper/(CC BY-ND)How We Approach Our Work
Our project is a partnership between the USC Wrigley Institute and Marine BioEnergy Inc., supported by the U.S. Department of Energy's ARPA-E MARINER (Macroalgae Research Inspiring Novel Energy Resources) program. The research team consists of biologists, oceanographers, and engineers, as well as scuba divers, vessel operators, research technicians, and students.
We examined kelp's biological response to depth cycling by attaching it to a structure we call the 'kelp elevator,' designed by our engineers. Located near the USC Wrigley Marine Science Center on California's Catalina Island, the elevator is powered by solar energy and moves the kelp between deep and shallow waters daily.
For three months, we depth-cycled 35 juvenile kelp plants, also planting a second set in a nearby healthy kelp bed for comparison. To our knowledge, this was the first study to examine the biological impact of physical depth cycling on kelp. Previous research focused on artificially pumping deep nutrient-rich water to the surface.
What Comes Next
Our findings suggest that depth cycling is a biologically feasible strategy for cultivating kelp. We now aim to explore factors that could enhance yields, such as timing, water depth, and kelp genetics.
There are still many aspects that require further investigation, including the processes needed for permitting and regulating kelp farms, as well as the potential ecological impacts of large-scale kelp farming. Nevertheless, we believe marine biomass energy holds immense promise in addressing sustainability challenges in the 21st century.
This article has been republished from The Conversation under a Creative Commons license. The original article can be found here.
Diane Kim is an adjunct assistant professor of environmental studies and senior scientist at the USC Wrigley Institute, USC Dornsife College of Letters, Arts and Sciences. Ignacio Navarrete is a postdoctoral scholar and research associate at the USC Wrigley Institute for Environmental Studies, USC Dornsife College of Letters, Arts and Sciences. Jessica Dutton is the associate director for research and an adjunct assistant professor of research at the USC Wrigley Institute for Environmental Studies, USC Environmental Studies Program, USC Dornsife College of Letters, Arts and Sciences.
