Eutrophication is a dirty word. I think. It describes a nutrient over-enrichment of a body of water, which results in numerous things, but most typically a pelagic dominated system and not much alive on the bottom. Not much. But some benthos thrive in these sorts of environments. Mainly, macroalgae. Many of these submerged algal species are tolerant of low light conditions, and outcompete other benthic producers when nutrients are aplenty. When you go to your local bay that is loaded with houses and development, typically you might find Ulva, also known as sea lettuce, and Gracilaria, a branching red alga. both are common in many marine systems, tolerant to low light, proliferate in nutrient rich environments, and, especially the case for Ulva, grow extremely fast.
However, recently, scientists are beginning to examine the use of these very macroalgae as a mode of cleaning up nutrified water bodies. This isn’t a new concept, though, as marine aquarists, and particularly those who keep living reefs, often use “algal scrubbers” and “turf algal filters” and “refugiums” where they keep an isolated tank or compartment with algae that the water from the tank has to circulate through. This helps keep their nutrients low and algae out of their main tanks, and this practice has been going on for decades. So why is science jumping on board now?
Maybe its because there is money to be made. Eutrophication is a major problem plaguing most coastal systems, and mitigation is a new big word in governments and funding agencies. We all know that plants require nutrients to survive and grow. Its simple biology that we probably learned sometime in elementary school (unless, of course, you are from Kansas, just kidding). Eutrophied systems have plenty of nutrients. Makes sense that adding plants, particularly fast-growing and low light tolerant species, would help use those nutrients. The concept is so simple to understand. Nutrients go in, plants use them up, and the water is cleaner. Obviously, there are associated problems with macroalgae, as they are often termed “nuisance species” due to their ability to essentially over-grow/smother everything and suck up all the oxygen during respiration and decomposition. But there are clear benefits.
This was recently in the news, as professor Charles Yarish from Stamford has been investigating the potential for algae to “purify” systems. He has worked with mussel farmers to grow kelp on their long lines to help mitigate the nutrient deposition by the mussels, and is currently investigating the feasibility of using Gracilaria as a natural purification method for the heavily polluted East River. His idea is to grow the algae on sets of longlines adjacent to lines full of ribbed mussels, with the hopes that this combo of filter feeder fast growing alga will be able to remove nitrogen and phosphorous from the water column. Obviously, this won’t be enough to clean up with river. But, if they look at the rate of nutrient uptake in combination with the growth rates and ending biomass of the algae and mussels, they can come up with a model of nutrient removal for the system. This would allow them to decide how much of each is necessary to clean up the East River. My guess is that the amount of biomass necessary to remove nutrients from the river is many, many, many boatloads. That being said, this will provide valuable information for managers around the country, and may ultimately lead to successful eutrophication mitigation attempts in smaller and less impacted waterways.
I’ll leave you with one of Yarish’s quotes from the article: “This kind of bioremediation effort hasn’t yet happened at an ecosystem level,” says Yarish. “We need to team the seaweed with the filter feeders. We want to do this at a level that hasn’t been seen before.”