Rising. Elizabeth Rush
littered throughout the Sprague,” Beverly chimes in. “And hundreds throughout marshes up and down the coast.”
A recent study released by the National Academy of Sciences predicts that as coastal wetlands continue to be transformed by atmospheric warming, they will release more methane into the air. But what makes a wetland vulnerable may be more complicated than its height and altitude. As Kimbra Cutlip wrote in a recent issue of Smithsonian magazine, “How much carbon wetlands take up, how much they release, how quickly soil accumulates … are all factors that are intertwined with one another and dependent upon a variety of influences. Like the tugging of one line in a tangled web of ropes, as one loop loosens, another tightens, changing the shape of the whole bundle.” When humans interfere with marsh hydrology—by ditching, plugging, draining, diking, culverting, and developing alongside and in these unique landscapes—they are yanking, even severing, the ropes that tie the marsh together.
In the short term, widening the culverts that restrict tidal flow, removing man-made infrastructure—things like ditch plugs and roadways—and reconnecting marshes to the rivers that have long provided the silt that fuels accretion would likely increase these important ecosystems’ ability to keep pace with sea level rise. However, as the rate of the rise itself accelerates, what tidal marshes will need more than anything else is space, room to migrate up and in. And, though few want to admit it, providing space will likely mean relocating some of the human communities we have built along the seashore.
Just below the buckled piece of plywood, Dana drops a Plexiglas chamber over a preselected square of healthy marsh vegetation. Joanna, who has spent much of the past year using the ring-down mass spectrometer to calculate net fluxes all around New England, lays the Science Box on two milk crates. She plugs the machine into a set of tubes that connect to the chamber. Then she presses a button and the Science Box begins to whir, almost immediately producing data. Everyone crowds in to look at the stream of numbers scrolling up the screen.
“Right now we aren’t seeing any methane emissions, which is what we want,” says Beverly. A molecule of methane, one of the most potent greenhouse gases on the planet, can, over the span of a decade, heat the atmosphere eighty-six times faster than a molecule of carbon dioxide. “And the carbon dioxide is dropping too, because the plants are photosynthesizing,” she adds. In essence, they have verified what they already know—healthy marshes are good at sequestering and storing greenhouse gases. The data gathered here, below the ditch plug, will serve as a control to measure the rest against. It takes only a few minutes for a heap of healthy cordgrass to become a set of numbers, a kind of bottom line.
After sampling three different areas where the ground is firm and the grass luxuriant, we move the field station back two hundred feet or so, above the ditch plug. The land starts sucking at our boots again, squelching and giving way beneath us as we plod in.
“An alternative name for my thesis might be ‘Measuring Marsh Farts,’” Dana jokes as he tries to keep his balance near a particularly pestilent pool covered in brown scum.
As the group prepares the fourth test site, a lanky research technician who hasn’t said much all morning points at the hollow of my throat and asks, “What’s with that necklace?”
For a second I am confused. I reach up and grasp a silver hexagon hanging on a silver chain, a Christmas present I hadn’t taken off since receiving it. “It was a gift,” I say. “Why?”
“It looks like a shorthand representation of the atomic structure of benzene.” Then he adds in a wooden voice, “It’s classified as a carcinogen in California.” The research technician breaks out into a wry and knowing smile, claps a hand on my shoulder, and laughs. I have come to adore science-geek small talk almost as much as I enjoy learning about the inner workings of these often-overlooked landscapes. Those who are devoted to tidal marshes are members of the same scattered and idiosyncratic tribe. They are more at home thigh deep in sulfurous mud than they are at the local shopping mall, and increasingly—as they bear witness, if not to the end of the world, then certainly to the end of one world—their humor has taken a turn for the macabre. “You have to laugh to keep from crying,” a geologist in the Everglades once told me.
The cavity ring-down mass spectrometer beeps, a warning that there is humidity in the lines. Benzene Man turns away from me and faces the malfunctioning machine. The crew disconnects and reconnects the hoses. The beeping continues.
“Science,” Beverly says over her shoulder. “Winging it every day.”
Once the water is cleared from the lines and we have all eaten a snack, the Plexiglas chamber is lowered over another square of marsh grasses. This time nearly half are rotten. For a moment the world goes silent, everyone leaning in toward the bleached-out computer screen. The first reading is 1.55 parts per million of methane, then 1.6 parts per million, then 1.7 parts per million. All the scientists let out a little yelp.
“It’s kind of twisted,” Beverly tells me, chuckling. “But when we see that methane increase, it’s good, in a way, because it means that our hypothesis is at least partially correct.”
Just as they supposed, the rotting patch of marsh grass above the ditch plug is contributing more methane and carbon dioxide to the atmosphere than the sample plot of the same size below. Beverly and her students suspect that the water infiltrating the marsh and now impounded by the ditch plug stimulates methanogens to spring into action, breaking down the organic matter the Sprague has long stored. A kind of fermentation follows that causes the marsh to decompose from within while also releasing methane and carbon into the atmosphere at an unprecedented clip. Tug at a couple of ropes and the shape of the whole bundle changes.
“I’m not opposed to the idea of ‘monkey wrenching’ the ditch plug,” says Laura Sewall, an eco-psychologist and the caretaker of the Bates-Morse Mountain Conservation Area, who has joined us for the second half of the morning. Laura is advocating the kind of small-scale act of eco-defense Edward Abbey once encouraged to reestablish healthy hydrological patterns in the American West. While localized interventions of this sort won’t do much to stem the threat sea level rise poses to our most vulnerable coastal landscapes, they can help to temporarily preserve a world worth rescuing. Removing the ditch plug surely is a step in the right direction: coaxing saltwater marshes back toward their original hydrology in the hopes that they will be able to, at least in the short term, rise with sea levels as they have in the immediate historic past.
Whether that immediate past is an appropriate analog for the future is an important question to ask. Sea levels are currently rising much faster than was previously predicted. James Hansen, a former NASA scientist who now teaches at Columbia University, recently published a controversial paper that suggests that the rate of the rise will continue to accelerate exponentially in the coming years. So much so that he predicts that by century’s end the world’s oceans will likely be many meters higher. In which case monkey wrenching the ditch plug isn’t likely to save the Sprague. Removing the human infrastructure, and in particular the road that runs along its upland edge, would provide space for migration, and might be the only chance the marsh has to make it into the next century.
Dana stands next to the Science Box and does some rough calculations on his phone. “It looks like the area above the ditch plug is releasing significantly more methane than the area below.”
“Methane,” Beverly reminds me, “is, generally speaking, thirty times more effective at trapping heat than carbon dioxide, making it the most potent, if short lived, of the world’s greenhouse gases.”
In that moment my desperation, of the monkey-wrenching sort, gives way to monumental uncertainty. If what is happening right now on the Sprague is also unfolding in impounded tidal marshes the world over, then the likelihood that we will witness widespread marsh collapse goes up. But no one knows whether it will go up by a factor of one or one hundred, because humans have never recorded these kinds of events before.
What we do know is this: each molecule of methane released into the air warms the oceans and the atmosphere, speeding up the rate at which glaciers and ice sheets are melting, which in turn accelerates the rate at which sea levels are rising, which diminishes the chances that a marsh