Why grow freshwater algae to sequester carbon when there's already a readily available supply of saltwater algae in the form of seaweed?
Take seaweed from ocean. Turn it into activated charcoal using solar pyrolysis. Bury the charcoal in farmland and marginal land to make terra preta. Terra preta sequesters carbon for hundreds of years and makes the soil more fertile, reducing the need for fossil-based fertilizers. Plant trees and grass on the marginal land.
>Take seaweed from ocean. Turn it into activated charcoal using solar pyrolysis.
Kelp and seaweed forests are vanishing due to ocean changes (as a result of climate change) and overfishing in coastal waters. It will only grow in water with a maximum depth that effectively limits it to coastal waters.
Then consider that you would need several orders of magnitude more area to grow it than currently exists.
For the solar pyrolisys too, you simply couldn't process it fast enough even if you found a way to grow it fast enough.
The seaweed route is even more unworkable than the algae would be.
Similarly I did the maths on using the 10 largest fresh water bodies (all other life in them be damned) to grow azolla and even THAT wouldn't even get us close to carbon neutral (a fraction of being carbon neutral) assuming 100% sequestration to anoxic depths.
There legitimately isn't a workable solution here, even if the entire planet came together, other than outright abandoning fossil fuels completely in addition to establishing new seaweed and kelp 'forests', reforesting land that has been clear cut, switching to permaculture for our food needs, outright abandoning cattle for food, etc.
Humans aren't going to extinct, but the next few decades will likely cause drastic changes in civilization as we know it and a couple centuries from now, barring multiple miraculous inventions and/or ET intervention, life for the common man will be incredibly different.
Good points... I had free-floating sargassum in mind,which is washing up in volume on beaches around the world, rather than kelp or something that has to be ripped up off the seabed.
Sargassum is in a state of hyper-growth around the world. something has created optimal conditions for it. I suspect that whatever was taken from the ocean would quickly be replaced. Is there a calculable upper limit to the amount of sargassum that could be produced by the ocean if it were aggressively being removed?
Not saying this idea is practical, but the goal was to be more practical than covering half the Sahara with algae growing ponds.
>Is there a calculable upper limit to the amount of sargassum that could be produced by the ocean if it were aggressively being removed?
I suppose the biggest limiting factor will be whatever minerals/nutrients it is taking from the water being in a sufficient volume in a given area. Although water temperature will probably matter considerably too.
Take seaweed from ocean. Turn it into activated charcoal using solar pyrolysis. Bury the charcoal in farmland and marginal land to make terra preta. Terra preta sequesters carbon for hundreds of years and makes the soil more fertile, reducing the need for fossil-based fertilizers. Plant trees and grass on the marginal land.