Bog

• 1. Introduction

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  A bog is a wetland that builds itself out of its own dead. Layer by layer, the remains of plants pile up and refuse to rot. Over centuries, that refusal becomes peat, soft and brown and spongy underfoot. In some places the landscape is covered many meters deep in it. The water that drains out of a bog runs the color of strong tea, stained by dissolved peat tannins. Walk across certain bogs and the ground itself trembles. Larger steps send visible ripples across the surface, and they can even make trees sway. How does a place this waterlogged and this acidic become one of the most important habitats for biodiversity, especially in lands otherwise settled and farmed? Why does it preserve a human body so perfectly that finders mistake it for a fresh corpse? And why, after thousands of years of patient growth, can a bog vanish in a single dry summer?

• 2. How Decay Stalls

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  Peat is the answer to a simple imbalance. Plant material in a bog grows slowly, but it decays even more slowly, and that gap is everything. The low fertility and cool climate keep growth sluggish. Saturated bog soils hold little oxygen, so decay nearly stops. Dead plants, often mosses and typically sphagnum, accumulate faster than they break down. Bogs form in poorly draining lake basins in cooler northern climates, where water at the ground surface sits acidic and low in nutrients. The defining trait is where that water comes from. A bog draws most of its water and nutrients from precipitation, a condition called ombrotrophic, rather than from mineral-rich ground or surface water. Rain carries no dissolved calcium, magnesium, or carbonate to buffer the natural acidity of atmospheric carbon dioxide, so a bog is always acidic. Peat is usually present thicker than 30 cm, the wetland stays nutrient-poor, and it counts as one of the four main types of wetlands. The names pile up alongside the peat: mire, mosses, quagmire, muskeg. Alkaline mires, fed by mineral-rich water, get a different name entirely. They are called fens, and they range from slightly acidic to slightly basic precisely because their water is rich in dissolved minerals.

• 3. A World That Eats Insects

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  Sundews and pitcher plants solve the nutrient problem by hunting. In a place too poor to feed them, carnivorous plants like Drosera and Sarracenia purpurea draw nutrients from invertebrates instead. Orchids take a quieter route, partnering with mycorrhizal fungi to pull nutrients from the ground. Bog myrtle, or Myrica gale, carries root nodules where nitrogen fixation supplies an extra source of nitrogen. Sphagnum is generally abundant, threaded with ericaceous shrubs that are often evergreen, a trait that may help them conserve nutrients. Sedges rank among the most common herbaceous plants, and in drier spots evergreen trees take hold, where the bog blends into surrounding boreal forest. The animals are just as specialized. Caribou, moose, and beavers find habitat here, alongside nesting shorebirds such as Siberian cranes and yellowlegs. The vulnerable bog turtle lives in these waters. English bogs shelter a yellow fly called the hairy canary fly, Phaonia jaroschewskii, and North American bogs host a butterfly named the bog copper, Lycaena epixanthe. In Ireland, the viviparous lizard, the only known reptile in the country, makes its home in bogland.

• 4. Shapes Of The Land

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  Valley bogs settle into gently sloping valleys and hollows. Peat fills the deepest part of the valley, and a stream may run across the bog's surface. Because they depend on ground or surface water, valley bogs occur only on acidic substrates, though they can form in relatively dry and warm climates. Raised bogs tell a slower story, one that begins as open water. Over centuries a lake progresses to marsh, then to fen, then to carr, as silt or peat fills it in. Eventually peat builds the land too flat for outside water to reach the center. That part becomes wholly rain-fed, and a shallow dome of bog peat rises, typically a few meters high, often ringed by fen where groundwater can still percolate in. Blanket bogs need cool climates with rain on more than about 235 days a year. There the ground stays waterlogged long enough for bog to spread over hilltops and slopes alike. They drape the hills of Ireland, Scotland, England, and Norway, and in North America gather mostly in Canada east of Hudson Bay. They do not occur north of the 65th latitude in the northern hemisphere. A quaking bog floats outright. Sphagnum moss anchored by sedges such as Carex lasiocarpa forms a mat roughly half a meter thick on water, where white spruce, Picea glauca, may even take root. The mat can spread to cover small lakes, and pieces may detach into floating islands. Rarest is the cataract bog, formed where a permanent stream sheets over a granite outcrop, keeping the rock wet without eroding it, leaving a narrow strip too precarious for any tree.

• 5. Fuel, Soil, And Smoke

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  More than 20% of home heat in Ireland comes from peat. After drying, peat has served as fuel for centuries, and it still burns in Finland, Scotland, Germany, and Russia. Russia leads the world in exporting peat for fuel, at more than 90 million metric tons per year. Ireland's Bord na Mona, whose name means peat board, was among the first companies to harvest peat mechanically, a practice now being phased out. Dried peat also feeds gardens, sold as moss peat or sphagnum peat to help soil hold moisture and to enrich it, and it works as a mulch. In the Islay whisky-producing region, distilleries use smoke from peat fires to dry the barley for Scotch whisky. The cost of all this extraction is steep. More than 90% of the bogs in England have been damaged or destroyed, and once peat is gone, restoring the wetland is difficult because peat accumulates so slowly. In 2011 the UK government announced plans to eliminate peat from gardening products. The bogs offer gentler harvests too: blueberries, cranberries, cloudberries, huckleberries, and lingonberries are gathered from the wild, while bog oak, wood partially preserved by the bog, has been made into furniture.

• 6. Bodies In The Peat

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  When the Tollund Man surfaced in Denmark in 1950, the people who found him thought they had stumbled on a recent murder victim. He was that well preserved. The anaerobic conditions and tannic acids of a bog can keep organic material remarkably intact, and researchers could even name his last meal: porridge and fish. The same chemistry, low oxygen joined with high acidity, has produced some of the best-preserved mummies known, with hair, organs, and skin intact, buried thousands of years ago after apparent Germanic and Celtic human sacrifice. Denmark also yielded the Haraldskaer Woman, and England gave up Lindow Man, found at Lindow Common. Finds of such material have come from Slovenia, Denmark, Germany, Ireland, Russia, and the United Kingdom, offering archeological insight reaching as far back as 8,000 years. Bogs preserve more than bodies. In County Mayo, Ireland, the Ceide Fields lay hidden under a blanket bog: a 5,000-year-old neolithic farming landscape complete with field walls and hut sites. Bog-wood, including ancient oak logs, has proven useful in dendrochronology. Stranger still is bog butter, large masses of fat usually held in wooden containers, thought to be stored food, both butter and tallow.

• 7. Carbon And Collapse

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  Bone material drawn from bogs has decayed faster since the first analyses in the 1940s. Fluctuations in groundwater and rising acidity in the lower reaches are attacking the rich organic material that bogs are prized for preserving. Oxygen has reached the lowest levels of some bogs, drying and cracking the layers. Temporary fixes, such as piling soil onto threatened areas, fail in the long term. The likely cause is extreme weather like dry summers, which lower precipitation and drop the groundwater table. In Arctic and sub-Arctic circles many bogs are warming at 0.6 degrees Celsius per decade, twice the global average. That heat turns a carbon sink into a source. The gradual accumulation of decayed plant material normally locks carbon away, but as bogs warm they release large amounts of greenhouse gases. If the peat decays, its carbon dioxide enters the atmosphere and feeds global warming. The scale of what is at stake is vast. The world's largest wetland is the peat bogs of the Western Siberian Lowlands in Russia, spanning more than a million square kilometres, while the Magellanic moorland in southern South America covers some 44000 km2. A 2014 expedition from Itanga village in the Republic of the Congo found a peat bog as big as England, reaching into the Democratic Republic of Congo. A 2019 paper led by Graeme T. Swindles showed peatlands across Europe drying rapidly in recent centuries from drainage, peat cutting, and burning. Because bogs take thousands of years to form, rewetting drained peatlands may be one of the most cost-effective ways to slow climate change, a repair measured against the 52 Tg of carbon the peatlands of the former Soviet Union were once calculated to pull from the air each year.