Field notes on things that run themselves
The Plant That Buries Its Own Water Supply
Walk out onto a raised bog and the shape of it ought to bother you. The ground in the middle is higher than the land at the edges — a low dome, metres thick, made of water and dead moss, sitting above the water table it should have drained into long ago. Nothing holds it up but the remains of the plant growing on top of it. And the moss on that surface is not drinking from the ground below. It cut itself off from the ground a long time ago, on purpose, by burying it.
Start with the plant. Sphagnum — peat moss — has no roots, and alternates two kinds of cell in its leaves: small green ones that photosynthesize, and large hollow ones, ribbed with spiral thickenings and punched through with pores, that are dead. They die on the way to maturity, which is the point of them. Empty, they hold water like a vase — wicking it up the stem cell by cell, some species carrying twenty-odd times their dry weight, so the living tip stays wet a foot above standing water. The moss hauls its own pond up with it.
Now the part almost everyone gets wrong. Sphagnum is famous for acidifying its own bog by ion exchange — cell walls rich in uronic acids whose carboxyl groups hold hydrogen loosely, so the moss pulls calcium and magnesium from the water and releases hydrogen in trade. Real chemistry, long described. But in 2010 Nadejda Soudzilovskaia and colleagues measured it against a control, screening twenty subarctic mosses: bog Sphagnum alongside the brown mosses of alkaline fens. Exchange capacity came out nearly identical in both, roughly 155 to 185 microequivalents per gram. Brown mosses carry the same equipment. Their fens stay alkaline anyway. What differed was how much of it was in use — the Sphagnum sites sat largely empty, the fen mosses’ nearly full — which turns the arrow around. Sphagnum’s sites are unspent not because the moss is a better acidifier but because bog water has almost nothing left to trade for. Living exchange capacity, the authors concluded, “does not play any considerable role in the fen–bog shift.” The agent they proposed instead is the peat: enough dead moss piled up to block alkaline groundwater from rising into the living layer. The moss does not neutralize the buffer. It buries it, and lives on rain.
So the dome is not a by-product. It is the organ — and it is built from a very thin margin.
Peat is what survives, and most of what the moss makes does not. The bog’s top layer, the acrotelm — ten to fifty centimetres, wet but still breathing — is where decay does its work, and on the standard accounting some ninety percent of the year’s growth is destroyed in transit. A tenth reaches the waterlogged catotelm beneath, where oxygen runs out and decomposition slows to a crawl. It does not stop. That is the whole story. Moss grows at the tip four to thirteen centimetres a year; peat, in western Washington, accumulates an inch every forty years. A hundred millimetres of moss for half a millimetre of bog.
R. S. Clymo drew out the consequence in 1984, and it is the most elegant thing in the subject. Input to the catotelm is roughly constant — fifty grams per square metre per year. But the catotelm decays everywhere at once, at a rate proportional to how much is down there. A young bog loses little, having little to lose; a deep one loses a great deal, because loss scales with the pile. Somewhere the curves cross, and past that the bog cannot deepen: every gram arriving is matched by a gram rotting below. Divide input by decay coefficient and you have the ceiling — five hundred kilograms per square metre, which at ordinary peat densities is a dome around five metres thick.
A bog at that limit has not slowed down. The moss on top grows exactly as fast as it ever did. What changed is that the bog is finally large enough to consume everything it is handed. It has been the same shape for centuries, and not one gram of it is the same gram.
Which makes the failure lopsided. Cut a ditch, the water table drops, and a column sealed from oxygen for four thousand years meets air along its whole depth at once. Drained tropical peat, past the first violent year of settling, sinks about five centimetres a year — and over eighteen years some ninety-two percent of that was not compaction but combustion without flame. Half a millimetre a year to build; fifty to unbuild. How much is at stake is less settled than it sounds: the best estimate for northern peatlands is 500 ± 100 gigatons of carbon, published figures for that same quantity run from 137 to 621, and the reason is simply that nobody has enough cores.
These pages have met a plant surviving a hostile world before, at a hydrothermal vent, where the poison belonged to the planet and life merely learned to eat it. This is the other direction. Nothing about a bog was there first. The acid, the waterlogging, the starvation, the dome — the moss made all of it from its own remains, faster than the world could take it apart. A thing that wins by dying badly enough, in one place, for long enough.
One loop I’m watching
Next: the Earth wobbles. Not the slow ceremonial precession, but a small free wobble of the rotation axis, about 433 days around, spotted by Seth Carlo Chandler in 1891. Friction in the oceans and the give of the mantle should have damped it away within a few decades of whatever set it off. It is still going, and something — most likely the weather, pressing unevenly on the sea floor — keeps knocking it back into motion at random. A planet ringing like a struck bell that never quite stops being struck.
Tip: the ← and → arrow keys move between issues.
Prefer feeds? Follow by RSS or JSON Feed.
Want something playable between issues? Thought Toys has its own email list and RSS feed.
New to The Standing Wave? Start here →