Rivers empty into oceans carrying many things that don't belong there: top soil (not bottom soil) and nitrogen runoff. Some people look at this as an environmental problem that is ongoing and makes a mess of an area in the seas with algae problems and fish kills.

Build a big divider and float for example the Mississippi waters on the gulf of Mexico over it's old path of destruction growing duckweed on top. It can take the runoff nitrogen and phosphates out of water. While you may have never eaten duckweed you certainly can. You can feed it to livestock with excellent even improved results and you can use it as fertilizer, just work it in the ground green. It has twice as much protein as soybeans and it gives algae a run for its money in growth rates. It will double like every week. The fact that it floats makes it quite manageable. It becomes an intertwined carpet with single hairs that stick down about four inches. it dampens waves. Harvesting equipment would be easy just push the carpet down and the young hairless plants separate off the top.

The farming area is a scalable making small trials and large investment decisions all a bit easier. Area can be partitioned off with floats and anchors and separated from the ocean by some sheet. You can easily make air-sea connections for dolphins or whatever with floating rings. This idea goes along well with robotic dredging and harvesting. Simply spread out enough area to slow the water and the soil particles will fall out for you. This is the stuff that makes "bottomland" such a good place for a farm in the first place. All of this is at a shipping hub and water transport is the cheapest.

When you get done with the water you may want to sell it as drinking or irrigation water to be piped west to West Texas, New Mexico and Arizona. Not much water makes it out of there as it is. Or you could just dump it, whatever is most profitable.
-- MercuryNotMars, Feb 02 2009

stuff on duckweed http://www.mobot.or...ckweed/duckweed.htm
charms of duckweed link [MercuryNotMars, Feb 02 2009]

Dead Zones http://www.grinning...-global-article.htm
These communists have pretty pictures and perhaps a few facts. [MercuryNotMars, Feb 02 2009]

My slightly similar idea Home_20seaweed_20farm
Seaweed is good [nineteenthly, Feb 03 2009]

Dead Zone Remediation Dead_20Zone_20Remediation
other and related dead zone schemes. [bungston, Feb 04 2009]

OK, so create a duckweed farm "delta" by partitioning river outflow and keeping it on top of the sea? Or do I misunderhend?

What's the engineering involved in your 'divider'?

I sort of like the idea. But I wonder if it's better to just turn the last mile of river into duckweed farm before it reaches the sea.
-- MaxwellBuchanan, Feb 02 2009


I'm confused how you are both channelling the river into a bed of duckweed so particulates drop out AND keeping the shipping channels open. Is there some deep water low flow zone turn off that ships can take? And how do you dredge under the duckweed without killing it? Angle rotating crops? If this works I assume all those particulates will build pretty quickly underneith the beds. What does the Duckweed do to the oxygen levels? I'd say you'd do better with mobile islands of duckweed say bordered with recycled plastic bottles anchored mid-channel and moved periodically. Maybe something that self dredged using water power onto a barge floating behind the island.
-- MisterQED, Feb 03 2009


You appear to understand [Maxwell] somehow I am imagining something like inflatable raft material. I leave a bit to the imagination I don't think the engineering is the big deal. if you can imagine a problem you can probably imagine the solution. Maybe hurricanes cause problems. Maybe it causes hurricanes. I imagine anchors are involved. the problem with the last bits of the river is that it is still flowing a bit fast and that would definitely get in the way of shipping lanes. Shipping lanes change in the river you can't make anything permanent because the river changes on you. you could put a lock and dam there and flood useful farmland and do something similar but I was finding new farmland. what better place than a deadzone? the climate down there is perfect.

[MisterQED] to start it might be something simple like a floating three foot pipe inlet that Isolates part of the river water. if you get on a scale that you can handle and process all the water when it isn't flooded and nitrates are most concentrated, then you have something like a lock and dam only you are not holding the water back you are diverting it out to sea. You simply lower a partition at the diversion point and they transfer onto river water, no waiting for the lock to fill. Scaling this to fit a tug and full compliment of barges so that you don't have to break it down like you have to do at other locks is just a matter of partition spacing you can probably get by on one partition so no spacing. at first you really don't need to worry about shipping lanes but as you get bigger you can make shipping lanes across your fields and tie both sides together with a deep anchored vein to conduct water. The only lain I know of goes in and out of the river and you can just divert your fields toward Texas where the dead zone is but this need not conflict with straight cuts across a large traffic area. I am pretty sure there is no fishing in the dead zone as it is now.

Duckweed is a floating plant it has a single hair that sticks down that doesn't take up water or serve anything but a mechanical right side up and communal function there is nothing impeding you from sticking a pool cleaner beneath the carpet or perhaps during harvest doing your dredging. Duckweed does exactly what the algae does as far as oxygen goes they both make oxygen in the process of making their carbon components. when they decompose they suck out oxygen. The thing is we collect the duckweed and cut out this cycle. Allowing it to grow without harvest does no good for anyone. Duckweed is not good for your lagoon because of this and it is good for your lagoon if you skim it off otherwise it goes anaerobic

I am pretty sure this does what environmentalists would want but I am mainly thinking that it only works if it makes money. This is probably the good kind of environmentalism like recycling aluminum, the kind of recycling that works. I emphasize the current dead zone because I doubt communists would go for it otherwise.

Dredging shes my drudgery Sailing shes my pride Bend my back to labor ride out on the tide that's been my joy since I's a boy
-- MercuryNotMars, Feb 03 2009


I like it and i've voted for it, but i want more. Duckweed will provide certain nutrients such as, presumably, folic acid, magnesium and protein, but i think you should also consider growing something like dulse or hijiki underneath for the mineral content which would otherwise be lost. Duckweed would cut out some of the light, but dulse is a rhodophyte and hijiki a phæophycean, so they'd be OK at low light levels. Some seaweeds also grow in fresh water, with lower nutritional content. Not sure about those.

Again, this is partly about multistorey farming.
-- nineteenthly, Feb 03 2009


//I don't think the engineering is the big deal//
[marked-for-tagline]
-- coprocephalous, Feb 03 2009


If you look closely at the Grinning Planet link, one of the maps appears to show an inland 'dead zone' somewhere near Melbourne; a place where no fish can live, perhaps because it's fifty miles from water.
-- pertinax, Feb 03 2009


No real objections to that [nineteenthly] It kind of sounds like it needs roots. If people pay enough money about any demand can be met. It does appear to be a saltwater plant. to a certain extent I like duckweed because I think it is already in Louisiana and I think it doesnt grow in salt water. I am sure the plants will have to vary according to geography. Monoculture has its benefits. I live in a corn and soybeans area and that is what we grow probably because that is what is most marketable because that is what the market is used to handeling in a specialized way. That is not to say that I don't grow tomatos. I imagine dredging the partition will be a focused thing. Rivers dump their loads in uniform piles (sandbars and gravelbeds) there will probably be places you don't have to dredge every day or even every month. If you have found the Soybeans to my Corn that is great. I can't say plant biology is my strongsuit. Maybe movable trays for them to tie to?

It occurs to me that this thing may collect barnacles on the underneath side. I have never had any experience with them. do you need a drydock approach for flexable surfaces?
-- MercuryNotMars, Feb 03 2009


The thing about duckweed is that in many places it's a real pest. Some will certainly escape your enclosure almost whatever you do. So you're probably limited to places where it isn't.

But using duckweed does seem attractive, I've been thinking about its potential for biomass production myself.
-- Loris, Feb 03 2009


Dulse has a holdfast, but seaweeds don't have roots so the important thing is what's in solution. I don't know about hijiki, but there are planktonic seaweeds which just float, such as Sargassum. I don't know about their edibility to humans, though eels eat it.
-- nineteenthly, Feb 03 2009


duckweed is a fun plant. I had the privlege of encountering some. I haven't heard about any being in the ocean and if it gets into a Louisiana pond I think it is safe to say it probably won't cause any new problems they haven't had to deal with already.

I do like correct terminology [nineteenthly] I guess that is what I had in mind but that helps in conveying the idea. if you can attach it to grates you can pick it up and vacuum under it.

While I am at it we might as well make the divider material reflective. After the first 20 miles the water will probably be clear. I have had a bit of experience with clay setteling out of water. You get a clear water on top really quickly and the clay continues to compress in what appears to be a uniform manner based on particulate size. The more homogenius the more uniform it seems. I am not sure what the speed threshold would be to a certain extent if there is no churning there is no particular speed. I am imagining a deep slow tank that takes the silt from the bottom first with an auger just using a more settled top layer to avoid churning. Its a massive project, if you try to take on the whole river, not that you have to start big. I am sure there are a few places that would like some fill. New Orleans could have used some.
-- MercuryNotMars, Feb 04 2009


If duckweed is a freshwater plant, and the farm is floating over salt water, that should prevent it from escaping the pen and overrunning any sensitive habitat.
-- BunsenHoneydew, Aug 09 2016



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