permaculture

[Lawrence London <lfljvenaura@gmail.com>]

On Fri, Oct 23, 2026 at 10:39 PM Lawrence London <lfljvenaura@gmail.com> wrote:

On Fri, Oct 23, 2026 at 10:24 PM Lawrence London <lfljvenaura@gmail.com> wrote:

Created in a conversation with Claude AI Assistant (which did most of the work):

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On 13 October a 0.5 L sealed aquarium launched to the International Space Station on SpaceX CRS-35. It’s a student experiment called SCAMPI, supported by ESA. It holds three Hawaiian red shrimp, some Chaetomorpha algae, and lava rock carrying microbial biofilm. It’s modeled on the commercial “Ecosphere” sealed aquariums, which can run for years with no inputs.

Its science lead, Patrick Grove, says the main goal is to confirm that nitrogen cycling still works in space. The microbes that do it are the same ones we depend on in soil, compost, and aquaponics, and no one has checked whether they survive and function in orbit. The team will run genomic analyses on the module when it returns.

How manure nitrogen becomes nitrogen gas, and comes back

The route from manure to N₂ is a real loop, and nitrogen-fixing organisms close it.

1. Ammonification. Manure nitrogen is mostly protein and urea. Microbes break these down into ammonium (NH₄⁺), and urease splits urea within hours to days. Ammonium and ammonia (NH₃) are in equilibrium, and higher pH pushes it toward NH₃.
2. Nitrification (aerobic). Ammonium becomes nitrite and then nitrate (NO₃⁻). This is the step SCAMPI is testing.
3. Denitrification (low oxygen). When oxygen runs out, many ordinary soil bacteria breathe nitrate instead. They step it down: NO₃⁻ → NO₂⁻ → NO → N₂O → N₂. The last step, N₂O to N₂, is done by the enzyme nitrous oxide reductase. When that step is skipped, the nitrogen escapes as N₂O, a strong greenhouse gas.
4. Anammox. In some anoxic zones, a separate group of bacteria combines ammonium and nitrite directly into N₂. It matters in wastewater and the oceans, and possibly in wet soils.

N₂ is 78% of the air and is inert to almost every organism. Only specialists with the nitrogenase enzyme can pull it back out of the atmosphere. These include rhizobia in legume nodules, free-living Azotobacter, cyanobacteria, and Frankia in alders. That is why legumes and cover crops matter in any closed system.

Ammonia volatilization is a separate loss. Fresh manure or urine on a warm, alkaline, or dry surface can lose a substantial share of its nitrogen as NH₃ gas straight to the air, without ever becoming nitrate.

• Why the carbon-to-nitrogen ratio matters. Microbes need roughly a fixed balance of carbon and nitrogen to grow. Too much carbon and they pull nitrogen out of the soil to build their bodies (immobilization). Too little and the surplus is released as ammonium (mineralization), which can then be lost as gas.
• What changes the ratio. Woody and fibrous materials like sawdust and straw are carbon-rich. Manure, urine, grass and kitchen scraps are nitrogen-rich.
• How the enzymes work. Urease, the nitrifier enzymes (ammonia and nitrite oxidation), nitrate reductase and nitrous oxide reductase, and nitrogenase, which is damaged by oxygen. That’s why legumes keep their nodules low in oxygen.
• Where the numbers come from. Why the commonly cited compost ratio is around 25 to 30 to 1, and why it is a rule of thumb rather than a constant.

Where the 25 to 30 to 1 compost ratio comes from. Microbial bodies are nitrogen-rich compared with their food. Bacteria and fungi are often cited as roughly 5 to 10 parts carbon per part nitrogen. Microbes also burn off much of the carbon they eat as CO₂ for energy, and only a fraction, often cited as around a third, goes into new biomass. If a microbe needs about 8 parts carbon per nitrogen in its body and builds only a third of the carbon it eats into that body, the food needs about 24 parts carbon per nitrogen. That is close to the 25 to 30 figure.

It is a rule of thumb, not a constant. Carbon in sawdust or wood chips is mostly slow-to-digest lignin, so the effective ratio is lower than the number on paper. Fresh grass clippings break down quickly and release their nitrogen sooner. Temperature, moisture and aeration also change the outcome. 

How the enzymes work. Each step of the nitrogen loop depends on a specific enzyme.

• Urease splits urea into ammonia and carbon dioxide. This is the first step when urine or manure breaks down.
• The nitrifier enzymes need oxygen. One group of microbes oxidizes ammonia to nitrite, and a second group oxidizes nitrite to nitrate.
• Nitrate reductase and nitrous oxide reductase work in low-oxygen conditions. Together with the steps between them, they let denitrifying bacteria convert nitrate to N₂O and then to N₂ gas.
• Nitrogenase is the enzyme that converts N₂ from the air into ammonia. Oxygen damages it, so nitrogen fixers have to keep oxygen away from it. Legumes do this in their root nodules with a protein called leghemoglobin. It holds free oxygen very low but still delivers enough to the bacteria for respiration.

Some of this is simplified. Several of these steps involve more than one enzyme, and the pathways differ somewhat between organisms.

 

Why space makes this interesting

With no buoyancy, nothing rises or convects, so oxygen reaches the biofilm mostly by slow diffusion from the aquarium’s one big central gas bubble. My guess, not the team’s, is that this creates low-oxygen pockets and tips the community toward denitrification and nutrient loss.

We see the same failure in compacted, waterlogged, or sealed-over soil. Nitrifiers need oxygen and grow slowly, so when pore space collapses, nitrate production stalls and nitrogen leaves as gas.

What this means in the garden

• Carbon. Mixing manure with plenty of straw, leaves, or wood chips gives microbes a sink for ammonium, so they build it into their own bodies instead of releasing it.
• Cover manure and urine. Burying them or covering with mulch cuts ammonia loss. Dilution and soil contact help too.
• Keep soil aerated and drained. This favors nitrate formation over denitrification.
• Avoid compaction and waterlogging. Both promote denitrification and N₂O. Hot, wet, layered compost piles can lose much of their nitrogen this way and as NH₃.
• Keep living roots in the ground. Plants take up nitrate and ammonium before microbes can send them off as gas.

Which loss route dominates depends on temperature, pH, moisture, and carbon supply, so be cautious with any single “typical loss” figure.

Whatever SCAMPI shows, it’s a rare controlled look at the minimum machinery of a closed nutrient loop. If the cycle holds in a tiny sealed tank with the usual mixing taken away, that says something about how robust it is. If it breaks, the data should show which step failed first.

One detail is unsettled. Grove’s post says the module returns after 3 to 12 months, while the project page says 90 days. I’ll pass along whatever turns up.

Sources:

• Project: https://thespringinstitute.com/scampi/
• ESA announcement: https://education.esa.int/student-built-scampi-experiment-launches-to-the-international-space-station/
• Grove’s r/Aquariums post, with video: https://www.reddit.com/r/Aquariums/comments/1xdol4q/my_shrimp_aquarium_is_currently_on_the/

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Lawrence F. London, Jr.
lfljvenaura@gmail.com

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Lawrence F. London, Jr.
lfljvenaura@gmail.com

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Lawrence F. London, Jr.
lfljvenaura@gmail.com