Pump oxygen and whatever bottleneck nutrient in and harvest algae. You’ll clean the excess nutrients out of the water and sink carbon at same time.
Do this in the Mississippi River delta for maximum effect, do a pilot in a Minnesota lake first.
I guess the trouble was only what to do with the algae. They expected it leave the lake, bringing the excess nutrients with it. How would you harvest it?
The trouble is that distributing compost is extremely expensive and it doesn’t release into the soil quickly.
You can truck out tons of dry fertilizer and irrigate with it, getting immediate results through a system you already have on farms. Your nutrient to dollar ratio is far better (in the short term).
You might know this already. My main intent of mentioning that is that I suspect that way of thinking is actually totally misguided. The externalities seem to be far too severe, and damage to soils seems unsustainable as well. I have a feeling if we sucked up the cost of distribution and application of natural fertilizers, in the not-so-long term we might actually see major turn around on several issues related to crops and fertilizer run off.
There is plenty of evidence for it, but the scale of fertilizer needed is insane. No idea how we’d make that shift. Dry fertilizers are incredibly dense forms of nutrients, and they’re so easy to get from factory to plant.
US universities have published a lot of research showing natural fertilizers do yield good crops with better disease resistance, but any farm using them would need to put more money and time into fertilizing and could expect smaller yields. If everyone plays that game, okay… But if a farmer independently decides to, they need to find a market willing to pay more. That’s exceedingly rare.
We need to collectively value this investment, otherwise it’s very hard for farmers to afford the shift. At least, this is based on my limited hobby gardening/researching understanding. Someone in agriculture would know better.
After harvesting do something similar to the process in the post. Dry it, pyrolyze, separate carbon goo from ash, bury one, use the other as fertilizer or another useful purpose.
Wolffia is the fastest growing plant on the planet and can double in size in a day. It's small, so it would work well as fuel for biomass reactors, the carbon char would be mostly derived from atmospheric carbon, resulting in a net negative, you can grow fish in the water underneath it, and it itself is edible and eaten already in many parts of the world where it grows naturally.
Further, it likes the slightly acidic water that bubbling CO2 into the water would create and it specifically oxygenates the water it floats in by stripping oxygen from CO2 during photosynthesis.
The downside is that no one has figured out the full process for continuously farming Wolffia yet, but if you solve that you can solve many other problems and create a multiple stream of income business out of taking carbon out of the air. (Biomass reactor fuel, plant food source for humans and animals, fish food source & selling carbon credits)
There is some nice hardware for achieving it.
I’d have to refuel about once a week.
Doing via CO2 bottle is the way I’d do it now and is how the impressive displays do it (for the ones I’ve seen).
I don’t think you would ever get approval for something like this in a public lake. Maybe in some private, artificial pond?
And there are something like 14,000 lakes in MN though many of them one might be tempted to call ponds :) no need to build an artificial one though, there are plenty.