A large seaweed farm in Asian. Via Adobe Stock.

Water bodies provide humans with many services including fresh water for drinking and agriculture, transportation, and recreation. Our ability to use these bodies of can be greatly hindered by excessive nutrient inputs.

Not unlike plants on land, phytoplankton, require sunlight and nutrients to grow. Nitrogen (N) and phosphorus (P) aren’t unnatural in waterways; nitrogen makes up approximately 78% of the atmosphere and naturally diffuses into water. Phosphorous occurs from rock weathering and soil erosion. Both nitrogen and phosphorous exist in growth stimulating molecules such as nitrate and phosphate.

But human activities have jeopardized the natural balance of these essential nutrients in water bodies. Large scale agriculture, wastewater runoff, and the destruction of natural filtration from wetlands have resulted in huge amounts of nutrients accumulating in bodies of water.

Wastewater runoff from agricultural and urban areas is a major contributor of nutrients to bodies of water.  Via Adobe Stock.

Excessive nutrient enrichment, or eutrophication, is a serious problem for rivers, lakes, and coastal oceans. Eutrophic waters hold many times more nutrients than what is typically the natural state. When extreme amounts of nutrients are concentrated into a small area, an algal “bloom” may form.

An algal bloom in a water reservoir.  Via Adobe Stock.

Impacts of algal blooms can be detrimental. These phytoplankton perform photosynthesis during the day but switch to respiration during the night, releasing carbon dioxide into the water. Phytoplankton blooms may also result in an increased concentration of the local zooplankton, which respire and release carbon dioxide. As a result, algal blooms can lead to poorly oxygenated waters. Dissolved oxygen sometimes becomes so low that it is harmful or even lethal to organisms. Additionally, some plankton species produce neurotoxins which can be dangerous at high concentrations. These “harmful algal blooms,” or HABs, can cause illness or death in humans and animals if they wade in contaminated water, consume organisms from the water, or drink the water (CDC).

A duck swims in a eutrophic pond.  Via Adobe Stock.

Eutrophication also poses serious economic impacts. Common (but not necessarily diagnostic) algal bloom characteristic are an unpleasant smell and appearance, scum or algal mats at the surface, dead organisms in the water, and a rotting smell (CDC). These conditions can be uncomfortable or even hazardous to enjoy. Efforts are sometimes made to mediate an algal bloom for recreation. In one case study, cleaning a coastal bloom of Ulva for the 2008 Beijing Summer Olmpics sailing event cost an estimated 30 million USD (Ye et al. 2011). Mediating phosphorus enriched lakes can require repeated treatments with aluminum (Angstam-Norlin et al. 2020). Red tides, a marine algal bloom caused by dinoflagellates, can cause huge economic losses via closing shellfish fisheries (Jin et al. 2008).

Recreation is often discouraged around red tides, as it can be dangerous to wade in or consume the water.  Via Adobe Stock.

Fisheries may have to close during red tides because organisms can accumulate toxins and pass them to humans during consumption.  Via Adobe Stock.

One strategy for preventing algal blooms in eutrophic waters is to utilize excess nutrients in a controlled, even beneficial fashion. Algae aquaculture, the farming and harvesting of seaweed, shows promise.

Like the unpleasant and harmful species that bloom, desired species of algae sequester nutrients in their cells. As long as the algae is removed from the water (i.e. harvested), the nutrients are removed from the system. Studies have shown beneficial effects of algae aquaculture (Xiao et al. 2017, Racine et al. 2021). Key differences between seaweed and terrestrial plants are that seaweed requires no freshwater and does not always need to be attached to the ground – some species are successfully grown on lines floating in the ocean. In eutrophic waters, seaweed also would not require additional nutrients for maximum yields. As a result, algae aquaculture is an incredibly enticing solution for mediating eutrophic waters.

An algae farm in Indonesia filters excess nutrients out of water.  Via Adobe Stock.

Currently, there are legal and social barriers halting large scale algae aquaculture in the United States. While the United States manages a large Exclusive Economic Zone, the marine area of which the country can set policy for, individual states have the ability to set regional regulations. Alaska and Maine are two hotspots for seaweed aquaculture, while New York has laws prohibiting commercial seaweed harvesting (The Guardian).

The consumer demand for seaweed is also low in the United States, especially when compared to Asian countries. Culinary creativity and new cultural trends may drive a greater demand for edible seaweed products. Barnacle Foods (Juneau, AK) produces kelp salsas and products using local Alaskan bull kelp. Monterey Bay Seaweeds (Moss Landing, CA) grows fresh seaweeds for local restaurants and fans. And growing interest in sushi and dried seaweed snacks bring algae to broader audiences.

Seaweed food sources are becoming more common, from high end cuisine to portable seaweed snacks.  Via Adobe Stock.

The seaweed industry could be one part of a multifaceted approach to reducing excess nutrients in waterways while creating a commodity in the process. Supporting seaweed businesses will help extend the reach of these products and drive future growth.

Referenced scientific papers

Agstam-Norlin O, Lannergård EE, Futter MN, Huser BJ. Optimization of aluminum treatment efficiency to control internal phosphorus loading in eutrophic lakes. Water Research. 2020;185. doi:10.1016/j.watres.2020.116150

Jin D, Thunberg E, Hoagland P. Economic impact of the 2005 red tide event on commercial shellfish fisheries in New England. Ocean and Coastal Management. 2008;51(5):420–429. doi:10.1016/j.ocecoaman.2008.01.004

Racine P, Marley AC, Froehlich HE, Gaines SD, Ladner I, MacAdam-Somer I, Bradley D. A case for seaweed aquaculture inclusion in U.S. nutrient pollution management. Marine Policy. 2021;129(April). doi:10.1016/j.marpol.2021.104506

Xiao X, Agusti S, Lin F, Li K, Pan Y, Yu Y, Zheng Y, Wu J, Duarte CM. Nutrient removal from Chinese coastal waters by large-scale seaweed aquaculture. Scientific Reports. 2017;7(April):1–6. doi:10.1038/srep46613

Ye N hao, Zhang X wen, Mao Y ze, Liang C wei, Xu D, Zou J, Zhuang Z meng, Wang Q yin. “Green tides” are overwhelming the coastline of our blue planet: Taking the world’s largest example. Ecological Research. 2011;26(3):477–485. doi:10.1007/s11284-011-0821-8

Other references

https://www.cdc.gov/habs/general.html

https://www.cdc.gov/habs/environment.html

https://www.theguardian.com/environment/2021/aug/26/new-york-seaweed-farming-kelp-producers

https://www.barnaclefoods.com/

http://www.montereybayseaweeds.com/