A bog, also called a bogland, is a type of wetland where layers of peat form from dead plant materials, such as mosses, especially sphagnum moss. It is one of four main wetland types. Other names for bogs include mire, quagmire, muskeg, and mosses. Fens are another type of wetland with alkaline soil. A bayhead is a specific kind of bog found in the Gulf Coast forests of the United States. These bogs often have heath or heather shrubs growing in sphagnum moss and peat. Over time, the slow decay of plant material in bogs stores carbon.

Bogs form in areas where the water on the ground is acidic and has few nutrients. They are usually found in soft, spongy areas made of peat, which is decayed plant matter. Bogs are common in cooler northern regions and often develop in areas where water drains poorly, such as old lake basins. Unlike fens, bogs get most of their water from rain, not from mineral-rich groundwater or surface water. Water that flows out of bogs is often brown because it contains dissolved tannins from peat. The cool temperatures and low nutrients in bogs slow plant growth, but decay is even slower because the soil has little oxygen. This slow decay allows peat to build up over time, sometimes forming layers several meters thick.

Bogs support unique communities of plants, fungi, and animals. They are important for biodiversity, especially in areas where land is used for farming or other human activities.

Distribution and extent

Bogs are found in many cold and temperate regions, especially in boreal ecosystems in the Northern Hemisphere. The largest wetland on Earth is the peat bogs of the Western Siberian Lowlands in Russia, which cover more than one million square kilometers. Large peat bogs also exist in North America, such as the Hudson Bay Lowland and the Mackenzie River Basin. Bogs are less common in the Southern Hemisphere, with the largest being the Magellanic moorland, which covers about 44,000 square kilometers in southern South America. Sphagnum bogs were once widespread in northern Europe but were often cleared and drained for farming. A study led by Graeme T. Swindles in 2019 showed that peatlands in Europe have dried quickly in recent centuries due to human activities like drainage, peat cutting, and burning. A 2014 expedition starting from Itanga village in the Republic of the Congo discovered a peat bog "as large as England" that extends into the neighboring Democratic Republic of Congo. Before large-scale deforestation in the 1800s, Ireland's geography was covered in boglands.

Definition

Bogs are a type of wetland, and it is hard to define them clearly because they vary in many ways. Wetlands are between land and water ecosystems, and different systems may use different rules to classify them. However, all bogs share some common features that help describe them:

• Peat is present and is usually more than 30 centimeters (12 inches) thick.
• Most of the water and nutrients come from rain (called ombrotrophic), not from groundwater or surface water (called minerotrophic).
• Bogs have very few nutrients, making them oligotrophic.
• Bogs are strongly acidic. However, bogs near the ocean may be less acidic because of salt from sea spray.

Since bogs contain peat, they are a type of peatland. As peat-producing ecosystems, they are also called mires, along with fens. Bogs and fens are different because fens get water and nutrients from mineral-rich groundwater or surface water, while bogs rely only on rain. Fens often have water that is slightly acidic or slightly basic because the minerals in groundwater help reduce acidity. Bogs remain acidic because rainwater lacks minerals like calcium, magnesium, and carbonate, which would otherwise neutralize the natural acidity from carbon dioxide in the air. The type of rock in the ground (bedrock) affects the minerals in groundwater, leading to differences in ions like manganese and iron. Bogs near coasts often have more sulfate and sodium because of their closeness to the ocean.

Ecology and protection

Bogs are home to many specialized animals, fungi, and plants. These organisms can survive in environments with very low nutrients and wet, waterlogged soil. Sphagnum moss is often found in large amounts, along with shrubs that belong to the ericaceous family. These shrubs are usually evergreen, which helps them keep nutrients. In drier areas, evergreen trees may grow, and the bog may blend into nearby boreal forests. Sedges are common plants in bogs. Some plants, like sundews (Drosera) and pitcher plants (such as Sarracenia purpurea), have adapted to the poor soil by catching insects for nutrients. Orchids use special fungi called mycorrhizal fungi to help them get nutrients. Some shrubs, like Myrica gale (bog myrtle), have root nodules where nitrogen is created, adding more nitrogen to the soil.

Bogs are important habitats protected by many government and conservation groups. They support mammals like caribou, moose, and beavers, as well as nesting shorebirds such as Siberian cranes and yellowlegs. Some reptiles, like the bog turtle, live in bogs. Bogs also have unique insects, such as the hairy canary fly (Phaonia jaroschewskii) in English bogs and the bog copper butterfly (Lycaena epixanthe) in North America. In Ireland, the only reptile found in the country, the viviparous lizard, lives in bogland.

The United Kingdom includes bog habitats in its Biodiversity Action Plan as a key focus for protection. Russia has large protected areas in the West Siberian Lowland. The highest level of protection is given to Zapovedniks (IUCN category IV), such as Gydansky and Yugansky.

Bogs are fragile ecosystems that are deteriorating quickly, as scientists have discovered. Bone material found in bogs has broken down faster than in the past, likely due to changes in groundwater and increased acidity in lower parts of bogs. These changes affect the rich organic material in bogs. Many areas have very little oxygen, causing layers of soil to dry and crack. Some temporary fixes, like adding soil to threatened areas, have not worked long-term. Dry summers, which reduce rainfall and lower groundwater levels, may be a main cause. Scientists think these problems will worsen as global temperatures rise. Bogs take thousands of years to form and create the thick peat used as a resource. Once destroyed, they are very hard to restore. In Arctic and sub-Arctic regions, bogs are warming at 0.6 °C every decade, twice as fast as the global average. Since bogs and other peatlands store carbon, they release large amounts of greenhouse gases as they warm. These changes have caused a major drop in biodiversity and species populations in peatlands across Northern Europe.

Types

Bog habitats can form in different places, depending on the weather and the shape of the land.

Bogs can be grouped based on their land shape, how close they are to water, how water reaches them, and how much nutrients they have.

Valley bogs form in gently sloping valleys or low areas. A layer of peat fills the deepest part of the valley, and a stream may flow across the surface of the bog. Valley bogs can develop in dry and warm climates, but they only form on acidic soil because they depend on ground or surface water.

Other bogs form from a lake or flat wet area, on either acidic or non-acidic soil. Over time, the area changes from a lake to a marsh, then to a fen (or valley bog on acidic soil), and finally to a carr as silt or peat builds up. Eventually, peat accumulates so much that water can no longer reach the center of the wetland. This area becomes fed only by rainwater, creating acidic conditions that allow a bog to form, even on non-acidic soil. Over time, the peat forms a shallow dome, which becomes a raised bog. The dome is usually a few meters high in the center and is often surrounded by fens or other wetland plants along the edges or near streams where groundwater can enter.

Raised bogs can be divided into several types:
• Coastal bog
• Plateau bog
• Upland bog
• Kermi bog
• String bog
• Palsa bog
• Polygonal bog

In cool areas with very high rainfall (more than about 235 days a year), the ground can stay wet for most of the year, creating conditions for bog plants to grow. In these places, bogs can cover large areas, including hills and slopes. While blanket bogs often form on acidic soil, they can also develop on neutral or slightly alkaline soil if acidic rainwater is more common than groundwater. Blanket bogs may occur in drier or warmer climates only in shaded areas where the ground does not dry out too often. In very cold climates, a patterned form of blanket bog called a string bog can form. In Europe, thin layers of peat without large surface features are found in Ireland, Scotland, England, and Norway. In North America, blanket bogs are mostly found in Canada east of Hudson Bay. These bogs are often still influenced by groundwater. Blanket bogs do not occur north of the 65th latitude in the northern hemisphere.

A quaking bog, also called a floating bog, is a type of bog that forms in wet parts of valley or raised bogs and sometimes near acidic lakes. The plants, mostly sphagnum moss held in place by sedges, create a floating mat about half a meter thick on water or very wet peat. White spruce trees may grow in these areas. Walking on the surface causes it to move, creating ripples or making trees sway. Over time, the floating mat may cover bays or small lakes. Bogs near lakes can sometimes break away and form floating islands.

A cataract bog is a rare wetland that forms where a stream flows over a hard rock surface, such as granite. The constant flow of water keeps the rock edges wet without eroding the soil, but the unstable ground prevents trees or large shrubs from growing. This creates a narrow, permanently wet habitat.

Uses

After peat is dried, it is used as a fuel and has been used this way for many years. More than 20% of home heating in Ireland comes from peat, and it is also used as fuel in Finland, Scotland, Germany, and Russia. Russia is the largest exporter of peat for fuel, sending over 90 million metric tons each year. Ireland's Bord na Móna, a company that harvests peat using machines, was one of the first to do so. This method is now being replaced gradually.

Dried peat is also used as a soil amendment, sold as moss peat or sphagnum peat, to help soil hold more water and improve its quality. It is also used as a mulch. Some distilleries, especially in the Islay region of Scotland, use smoke from peat fires to dry barley used in making Scotch whisky.

Once peat is removed from bogs, it is hard to restore the wetland because peat forms very slowly. More than 90% of bogs in England have been damaged or destroyed. In 2011, the UK government announced plans to stop using peat in gardening products.

Peat in bogs helps store carbon. If peat decays, it releases carbon dioxide into the atmosphere, which contributes to global warming. When undisturbed, bogs act as carbon sinks, absorbing carbon from the air. For example, peatlands in the former Soviet Union were found to remove 52 teragrams of carbon from the atmosphere each year. Rewetting drained peatlands may be one of the most effective ways to reduce the effects of climate change.

Peat bogs also help store fresh water, especially in the upper parts of large rivers. The Yangtze River, one of the world's largest rivers, begins in the Ruoergai peatland in Tibet.

Wild berries such as blueberries, cranberries, cloudberries, huckleberries, and lingonberries are collected from bogs. Bog oak, wood preserved by bogs, is used to make furniture.

Sphagnum bogs are also used for outdoor activities like ecotourism and hunting. For example, many canoe routes in northern Canada pass through peatland areas. However, some activities, such as using all-terrain vehicles, can harm bogs.

Archaeology

Bogs have special conditions that help preserve organic materials for a long time. These conditions include low oxygen levels and the presence of tannic acids. Scientists have found well-preserved materials in bogs in Slovenia, Denmark, Germany, Ireland, Russia, and the United Kingdom. Some bogs have preserved ancient wood, like old oak logs used in the study of tree rings to determine age. Bogs have also preserved human remains, such as bodies with hair, organs, and skin still in good condition. These bodies were buried thousands of years ago, likely as part of Germanic and Celtic religious rituals. Examples of these preserved bodies include the Haraldskær Woman and Tollund Man in Denmark, and Lindow Man in England. When Tollund Man was discovered in 1950, people first thought he was a recent murder victim. Researchers later found that his last meal before death was porridge and fish. This preservation happens because bogs have very little oxygen and are highly acidic. These conditions create some of the best-preserved mummies, giving archaeologists valuable information about ancient societies as far back as 8,000 years. In Ireland, the Céide Fields in County Mayo, a 5,000-year-old Neolithic farming area, has been preserved under a blanket bog, including field walls and hut sites. Another item found in bogs is bog butter, which consists of large amounts of fat, often stored in wooden containers. These were likely used to store butter and tallow.

Image gallery

• Sphagnum moss growing with northern pitcher plants at Brown's Lake Bog in Ohio, United States
• A bog located in Ostfriesland, Germany
• Rainwater collects in many bogs, creating pools of water, such as Koitjärve bog in Estonia
• Bog-wood and large rocks found at Stumpy Knowe near South Auchenmade, Ayrshire, Scotland, United Kingdom