Seaweed is not just for making sushi rolls. In recent years, seaweed farming has become a global agricultural practice, providing food, source material for various chemical uses (such as carrageenan), cattle feeds, and fertilizers.
Because of their importance in marine ecologies and for absorbing carbon dioxide, recent attention has been on cultivating seaweeds as a potential climate change mitigation strategy for biosequestration of carbon dioxide, alongside other benefits like nutrient pollution reduction, increased habitat for coastal aquatic species, and reducing local ocean acidification.
Seaweed that grows in a river estuary – the “mouth” of a large river where the tide meets the stream –can absorb nitrogen, thus conforming to environmental standards and preventing coastal pollution. This actually produces a natural decontamination facility of both significant ecological and economic value, according to researchers at Tel Aviv University (TAU).
Some seaweeds are microscopic, such as the phytoplankton that live suspended in the water column and provide the base for most marine food chains. Some are enormous, like the giant kelp that grow in abundant “forests” and tower like underwater redwoods from their roots at the bottom of the sea. Most are medium-sized, come in colors of red, green, brown, and black, and randomly wash up on beaches and shorelines just about everywhere.
The new study by TAU scientists and colleagues at the University of California, Berkeley proposes a model according to which the establishment of seaweed farms in river estuaries significantly reduces nitrogen concentrations in the estuary and prevents pollution in estuarine and marine environments.
The study was headed by doctoral student Meiron Zollmann, under the joint supervision of Prof. Alexander Golberg of the TAU’s Porter School of Environmental and Earth Sciences and Prof. Alexander Liberzon of the university’s School of Mechanical Engineering at the Fleischman Faculty of Engineering. The study was conducted in collaboration with Prof. Boris Rubinsky of the Faculty of Mechanical Engineering at UC Berkeley. The study was published in the prestigious journal Communications Biology under the title “Multiscale modeling of intensive macroalgae cultivation and marine nitrogen sequestration.”
As part of the study, the researchers built a large seaweed farm model for growing the ulva species (chlorophyceae) green macroalgae in the estuary of the Alexander River, which is located in the Emek Hefer region of Israel’s Mediterranean coastal plain. It runs the whole width of Israel to its estuary near Moshav Beit Yannai.
The Alexander River was chosen because the river discharges polluting nitrogen from nearby upstream fields and towns into the Mediterranean Sea. Data for the model were collected over two years from controlled cultivation studies.
The researchers explained that nitrogen is a necessary fertilizer for agriculture, but unfortunately, it comes with an environmental price tag. Once nitrogen reaches the ocean, it disperses randomly, damaging various ecosystems. As a result, the state local authorities spend a great deal of money on reducing nitrogen concentrations in water, following national and international conventions that limit nitrogen loading in the oceans and seas, including in the Mediterranean Sea.
“My laboratory researches basic processes and develops technologies for aquaculture,” explained Golberg. “We are developing technologies for growing seaweed in the ocean in order to offset carbon and extract various substances such as proteins and starches, to offer a marine alternative to terrestrial agricultural production. In this study, we showed that if seaweed is grown according to the model we developed, in rivers’ estuaries, they can absorb the nitrogen to conform to environmental standards and prevent its dispersal in water and thus neutralize environmental pollution. In this way, we actually produce a kind of natural decontamination facility with significant ecological and economic value since seaweed can be sold as biomass for human use.”
The researchers said that the mathematical model predicts farm yields and links seaweed yield and chemical composition to nitrogen concentration in the estuary. “Our model allows marine farmers, as well as government and environmental bodies, to know in advanc, what the impact will be and what the products of a large seaweed farm will be – before setting up the actual farm,” added Zollman. “Thanks to mathematics, we know how to make the adjustments also concerning large agricultural farms and maximize environmental benefits, including producing the agriculturally desired protein quantities.”
“It is important to understand that the whole world is moving towards green energy, and seaweed can be a significant source,” commented Liberzon, “and yet today, there is no single farm with the proven technological and scientific capability. The barriers here are also scientific. We do not really know what the impact of a huge farm will be on the marine environment. It is like transitioning from a vegetable garden outside the house to endless fields of industrial farming. Our model provides some of the answers, hoping to convince decisionmakers that such farms will be profitable and environmentally friendly. Furthermore, one can imagine even more far-reaching scenarios. For example, green energy.”
Liberzon added that “if we knew how to utilize the growth rates for energy in better percentages, it would be possible to embark on a one-year cruise with a kilogram of seaweed, with no additional fuel beyond the production of biomass in a marine environment.”
“The interesting connection we offer here is growing seaweed at the expense of nitrogen treatment,” concluded Golberg. “In fact, we have developed a planning tool for setting up seaweed farms in estuaries to address both environmental problems while producing economic benefit. We offer the design of seaweed farms in river estuaries containing large quantities of agriculturally related nitrogen residues to rehabilitate the estuary and prevent nitrogen from reaching the ocean while growing the seaweed itself for food. In this way, aquaculture complements terrestrial agriculture.”