We’ve all seen algae: pond scum in ditches, seaweed at the shore, green slime in aquariums. Perhaps you already know that the word algae doesn’t refer to closely related organisms descended from a recent common ancestor (like mammals or fungi). Rather, it refers to the organism’s appearance and behavior (phenotype, not genotype). Essentially any aquatic organism that produces oxygen using sunlight and isn’t a green plant (which are closely related to each other) is an alga. They are ubiquitous wherever there is light and water; indeed algae are hard to eradicate. Consequently, if you actually want algae, it is easy to help them proliferate – simply make them feel at home. The only caveat is that if what you want is a specific strain of algae in a pure form, that can be rather labor and capital intensive.
Pedantry conservation notice: alga is singular, algae is plural. As with datum/data, some folks will insist that you say “the alga is” and “the algae are”. I instinctively align with this sort of prescriptivity, but stylistically I usually find it awkward. Know that I am aware of and am willing to live with that. I use algae as both plural and mass noun, depending on how it scans in my sentences.
But back to our topic: why would anybody want to farm, say, hectares of algae open to the environment rather than square meters of it in transparent containers (here I ignore seaweed farming)? Except as a source of some foods, lab products, and specialty chemicals, there’s not much of a market for it. Algae itself, at least as a bulk nonspecific biomass, the kind you get when you can’t be bothered to go to the effort to cultivate specific strains, isn’t worth much: more expensive than dirt, but only slightly more useful.
The value of growing algae arises from the cultivation process itself. Because algae grows so rapidly, it can be utilized to recapture the nitrogen and phosphorus, from agriculture and municipal wastewater, that pollute our aquifers and surface waters. Where this polluted water is otherwise unpolluted, the biomass can be used as a fertilizer and soil amendment. Phosphorus, a finite mineral resource, is especially important as it is the basis of our high-performance agriculture. Nitrogen fertilizer consumes something like one percent of global energy, or about four percent of global natural gas production. Algae growth also fixes carbon. Returning this carbon to the soil can help revive its fertility.
Working to expand algae cultivation is my chosen humanitarian effort (do you have one? What is it?). I favor a practice called algal turf scrubbing (ATS, invented by my former boss Walter Adey, emeritus algae curator at the Smithsonian), which basically creates an artificial stream ideally suited for algae growth. Push practically any surface water (fresh or marine), through one of these channels, and the algae simply proliferate without extra help. The stream can be as wide as you want; it might better be called an aquatic field. Frequently removing the biomass allows more algae to take its place, maintaining rapid growth and thus rapid nutrient uptake. The only problem (if that’s the right word) is handling the biomass. Even though ATS algae is pretty cheap, it still costs about $500 per ton to grow, costlier than the fertilizer it recycles. This situation is a failure of the so-called “free market”, ironically a form of socialism as it ignores or even denies the externalities of pollution and unsustainability in order to present as net beneficial. Governments and other authorities should compare the costs and effectiveness of all functional solutions to the nutrient pollution problem and implement regulations or simply pay bounties to implement the best choices. Obviously I think ATS will be a player in any such competition.