Seaweed Farms in River Estuaries Reduce Nitrogen Concentrations

Anew study found that planting seaweed farms near river estuaries significantly reduces nitrogen concentrations in the river and prevents environmental pollution in streams and oceans.

The research was led by doctoral student Miron Zulman, under the joint counseling of Prof. Alexander Golberg of the Porter School of Environmental and Earth Sciences and Prof. Alexander Liberzon of the School of Mechanical Engineering at Tel Aviv University. The project was conducted in collaboration with Prof. Boris Rubinsky of the Faculty of Mechanical Engineering at the University of California, Berkeley and was published in the journal Communications Biology.

As part of the study, the researchers built a large kelp seaweed farm model for growing Mediterranean stalk kelp near the Alexander River estuary, hundreds of meters from the open sea. The Alexander River was chosen because the river discharges polluting nitrogen from nearby upstream fields and settlements into the Mediterranean Sea. Data for the model were collected over two years from controlled cultivation studies.

Nitrogen is a necessary fertilizer for agriculture, but it comes with an environmental price tag. Once nitrogen reaches the ocean, it disperses randomly, damaging various ecosystems. As a result, the state currently spends a great deal of money on treating nitrogen concentrations in water, and there are international agreements that limit nitrogen loading in the oceans, including in the Mediterranean Sea.

“My laboratory researches basic processes and develops technologies for aquaculture,” said Prof. Golberg. “We are developing technologies for growing seaweed in the ocean to set carbon and extract various substances from them, such as proteins and starches. In this study, we showed that if seaweed is grown according to the model we developed, close to streams and rivers’ estuaries, they can absorb the nitrogen to conform to environmental standards and prevent its dispersal in water, thus neutralizing pollution. In this way, we 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 add that the mathematical model predicts farm yields and links seaweed yield and chemical composition to nitrogen concentration in the river. “Our model allows marine farmers, as well as government and environmental bodies, to know, in advance, what the impact will be and what the products of a large seaweed farm will be — before setting up the actual farm,” says Miron 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 kelp can be a significant source,” said Prof. 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 decision-makers that such farms will be profitable and environmentally friendly.

“The interesting connection we offer here is growing seaweed at the expense of nitrogen treatment,” concludes Prof. Goldberg. “In fact, we have developed a planning tool for setting up seaweed farms in river estuaries to address both environmental problems and derive economic benefit. We offer the design of seaweed farms in streams and rivers containing large quantities of agriculturally related nitrogen residues to rehabilitate the stream and prevent nitrogen from reaching the ocean while growing the seaweed itself for food. In this way, aquaculture complements terrestrial agriculture.”