Sphagnum moss is an ecosystem engineer, much like many others found in nature. Think dam-building beavers or underwater forests of kelp. In this case, though, think bogs.

When certain species of sphagnum come together in open wetlands, they constrict the flow of water to a trickle, then rapidly and relentlessly metabolize available nutrients and cations (positively charged nutrient ions). The result is a wetland with very acidic, nutrient poor, stagnant water in which only the hardiest species can grow. Namely, more sphagnum.

Here’s where things get weird: when this sphagnum dies, its doesn’t decompose — at least not very fast. It’s preserved by the acidic waters in which it swims, pickled by its very own vinegar, soaking up and storing moisture with intact capillaries. It becomes peat, the undead moss of days gone by. But where, then, does the next generation of sphagnum grow? Atop the peat, of course, each generation layered over the last.

This is how bogs are born, and how they grow, swelling like inflatable mattresses of biomass: living moss on top, dead peat below. The ability of bogs to pack away peat makes them one of the most important carbon sinks we’ve got. Peatlands (of which bogs are one example) account for only three per cent of all land but contain 30 per cent of all soil carbon. North of the 45th parallel, peatlands sequester an average of 23 grams of carbon per square metre per year.

“It’s often quoted that peatlands contain more than twice as much carbon as the world’s forests,” says hydrogeologist Lauren Somers of Dalhousie University.

Big Meadow Bog, on Brier Island, Nova Scotia, is 65 hectares in size and about 750 years old, with its claim to fame being the Eastern Mountain avens — one of the most endangered plants in Canada — growing on its border, and, more recently, the herculean efforts dedicated to its restoration.

This bog was “ditched” and drained in 1958, then abandoned when crops wouldn’t take. Several unpleasant things happen when you drain a bog. For one, its stored peat is exposed to air for the first time in centuries, and begins to rapidly decompose, releasing carbon dioxide and methane like an uncapped gas well. If nutrients find their way back into the system — via fertilizer, for example — they are “volatilized” by the acidity, producing powerful greenhouse gasses like nitrous oxide, and supporting the invasion of less hardy species (which wouldn’t survive in a more acidic environment), like raspberries and trees — in this case, black spruce.

“This all happens very quickly,” says Nick Hill, botanist and ecologist with the Southwest Nova Biosphere Reserve Association. “Your bog can do one of two things. It can keep sequestering carbon and maintain its carbon storage, or you can drain it and send that carbon away.”

Choosing the former option, a coalition of conservation, research, academic, and governmental institutions came together in 2017 to restore Big Meadow Bog. That year, 150 ditch blocks were installed throughout the bog, and almost immediately the water table began to rise, submerging old peat and drowning the roots of invading trees. From there, sphagnum should have reasserted control, and probably would have, had it not been for the gulls.

When the wetland initially dried, a colony of Herring gulls — attracted to nearby mink farms – established itself in Big Meadow Bog and began bombarding its interior with nitrogen and phosphorous. It was assumed, said Hill, they would relocate when things got wet, but they didn’t. Instead, they built their nests a little higher, on piles of leaf litter beyond the reach of the restored water table, clinging stubbornly to habitat no longer ideal. Their droppings are forestalling the bog’s recovery, amounting to chemical warfare.

“We’re still seeing sphagnum come back,” says Hill. “But we’ve got a fight on our hands, between the nutrients the gulls are bringing in, and the sphagnum which is trying to absorb those nutrients and recreate acidity. If the gulls weren’t fertilizing the ecosystem, we’d have the bog back.”

It’s important to preserve pristine bogs, says Hill, both for their carbon storage and sequestration, but it’s equally important to restore damaged ones. There are several in Nova Scotia, he says, especially in the Annapolis Valley, which have been ditched and abandoned. Big Meadow Bog was meant to be a proof-of-concept, a blueprint for others to follow, and if the gulls can be convinced to leave, it should become exactly that. So far, however, no solution’s been settled upon, and the bog remains two-thirds unrestored.

“We want to show that restoration is possible,” says Hill. “If we find out how to stop the gulls, it’ll only take about 25 years for the rest of the bog to go back to normal.”

The Climate Story Network is an initiative of Climate Focus, a non-profit organization dedicated to covering stories about community-driven climate solutions.