In May 2019 the Mississippi River dumped a daily average of more than 5,000 metric tons of nitrate and 800 metric tons of phosphorous into the Gulf of Mexico, the highest levels in the past 40 years. These excess nutrients from Midwest farm fertiliser and animal waste rob the waters off Louisiana, Mississippi and Texas of oxygen, fuelling toxic algal blooms and causing what’s come to be known as a dead zone.
The size varies each year, but this particular patch’s five-year average hovers at about 13,000km2. To date, a US government task force has made little if any progress towards the goal of reducing it to 5,000km2.
For environmental experts the problem seems intractable. Known as eutrophication, dead zones are proliferating all over the globe. There are now more than 700 coastal areas worldwide that are either dead zones or negatively impacted by runoff. While the US suffers mostly from agricultural waste, urban wastewater is the main culprit in South America, Asia and Africa.
Every year, they inflict $3.4bn (about R46,5bn) in economic damage in Europe and the US alone due to lost tourism and fishing, declining property values, water treatment and adverse health impacts. In the past 10 years 85 US communities have spent more than $1bn (about R14bn) combined to prevent or treat algal blooms. Among the hardest hit are at the mouth of the Mississippi, where the constant ejection of waterborne waste from America’s heartland decimates local seafood and tourism industries.
But there may be a solution on the horizon. A new study makes the case that the Gulf of Mexico could trade in its slimy algae for silky green seaweed, which, if planted in sufficient numbers, could soak up much of that damaging waste. The concept is in its early days and implementation further afield, but given the lack of progress on other fronts, said study co-author Phoebe Racine, “there’s no other option but to consider alternative practices”.
Cultivating multiple species of seaweed in less than 1% of Gulf of Mexico waters could potentially help the US achieve pollution reduction goals that have been out of reach, said Racine, a researcher at the University of California in Santa Barbara. She and her colleagues have already mapped suitable areas for seaweed farms in the Gulf and found more than 62,000km2 of potentially available sites.
Farms of three major seaweed species and two shellfish species (all filter feeders that require no additional food) took up the equivalent of 5.7% of the carbon dioxide and 8.6% of the nitrogen discharges from all wastewater treatment plants in Korea.
— Marine scientist Jang Kim
Seaweed aquaculture dates back 1,700 years to China. These days, nations such as Indonesia and the Philippines, with China and South Korea, lead the world in this arena. In the latter, where aquaculture has grown 300% over the past 30 years, an intensive effort has demonstrated its usefulness as a waste reduction tool. As one of the biggest producers of seaweed in Asia (where 99% of all seaweed is cultivated), the country has at least 2,144 seaweed farms covering 900km2, according to Jang Kim, a marine scientist based at Incheon National University. That’s an area roughly the size of Johannesburg.
Farms of three major seaweed species and two shellfish species (all filter feeders that require no additional food) took up the equivalent of 5.7% of the carbon dioxide and 8.6% of the nitrogen discharges from all wastewater treatment plants in Korea, according to a study conducted by Kim.
Key to the success of seaweed farming is its increasing commercial potential and that these aquatic plants can soak up excess nitrogen and phosphorous and turn it into not only human food, but an expanding array of additional commercial uses. The most cultivated seaweeds include red or brown algal species or kelps. Some are used to make culinary thickening agents or agar to culture bacteria in laboratory settings. Others are dried into sheets called nori, used to make sushi rolls. While sugar kelp can be used as a sweetener, kelps are also used in toothpastes, shampoos, frozen foods and pharmaceuticals.
Making seaweed farms profitable will be a critical consideration to promoting them as a solution to agricultural and urban waste. Asia has strong existing demand for seaweed. Human consumption, including everything from sushi rolls to broth to salad, is the biggest market for harvested seaweed, said Kim. But growing demand can also be seen among the cosmetics and fertiliser industries, as well as feed for farmed seafood. “We have more than 50% of kelp production going to abalone feed,” said Kim.
Mass aquaculture faces some significant obstacles, not least of which is its labour-intensive nature. Seaweed cultivation relies on lab-based nurseries to grow and attach juvenile seaweed to netting or line or transferring cuttings from mature plants to a submerged line. Harvesting usually involves multiple people on boats cutting seaweed out of the water.
Globally, demand for seaweed is projected to double to $30bn (about R411bn) by 2025. In the US, however, the seaweed market is relatively small. Gretchen Grebe, an aquaculture scientist based at the Marine Biological Laboratory in Woods Hole, Massachusetts, said seaweed farming in American “is still very much in its R&D (research and development) phase”. She’s been studying coastal seaweed aquaculture in Maine, where in 2020 kelp farmers harvested about 218,600 wet kilograms, worth just shy of $300,000 (about R4,1m). (Also in Maine, a company received $11m in seed funding to grow kelp and then sink it into the deep ocean for carbon credits.) Racine contends that carbon credit markets used to slow pollution “could be used more fully” to encourage seaweed extraction of pollutants, including nitrogen, carbon and even heavy metals, from coastal areas.
“Using seaweed aquaculture to remediate any substantial quantities of nutrient pollution will require a massive expansion — the current scale of cultivation won’t even make a dent,” Grebe said.
In the US, the states have wildly divergent regulations when it comes to aquaculture permitting. While it’s comparatively easy to get a seaweed farm permit in Maine and Alaska, in California it requires negotiating a maze of overlapping regulations.
“Offshore operations are where the promise lies,” said Bailey Moritz, programme director for World Wildlife Fund (WWF). “Our goal is to see seaweed grow in a way that will have meaningful impacts [on nutrient depletion], and scale is necessary for that.” The WWF invested in Ocean Rainforest in the Faroe Islands, an operation that designed rigs to withstand offshore weather conditions.
But large-scale, offshore seaweed operations are still at least a decade away in the US, she predicted, and likely only if biofuels, bioplastics and animal feed create enough demand.
And while the US department of energy has invested $35m (about R480m) into researching seaweed-based biofuel development, with pilot projects starting in Puerto Rico, to date the Army Corps of Engineers has granted only one permit for a seaweed project in the Gulf of Mexico, according to Nakeir Nobles, a spokesperson for the organisation. Nobles said further hurdles include siting, Endangered Species Act consultations, design plans that prevent entanglement of sea animals and public education.
Seaweed has enormous promise, said Grebe, but scientists are quick to point out that it’s imperative to reduce upstream waste inputs as well. “We’re asking a lot of seaweed aquaculture to take care of the nutrient waste we dump into the Gulf,” she said.
— Bloomberg News. More stories like this are available on bloomberg.com
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