Swamps, marshes and bogs are not the same thing. Strictly speaking, they are varieties of wetlands. This family of ecosystems is a stretch of land saturated with water, neither fully land nor sea. Wetlands may be found on the edges of oceans, lakes or rivers, or be regions unto themselves. They are crucial pillars of the world’s biodiversity.
Wetlands are buffers for storms and strong winds and absorb excess water from rainfall and flooding. They serve a crucial ecological function by naturally filtering chemicals, metals and pollutants in their soil. As insects breed in them, they are also rife with disease. At the bottom layer, wetlands may house coal, while bogs and fens house peat, a valuable biofuel.
World folklore depicts wetlands – swamps and bogs, in particular, as dangerous haunted places, home to real dangers like alligators and tigers, and imaginary ones like witches and bunyips.
There are four types of wetland: swamps, marshes, bogs and fens. These differ considerably by the plants that grow in them.
Swamps are forested wetlands. Wooded plants dominate these regions, growing beneath the water and rising high above it. Saltwater swamps are found on tropical coastlines, freshwater swamps inland. Swamps tend to be humid and rich in wildlife. Famous swamps include the Bayou of Louisiana and the Mangrove Forests of Southeast Asia.
Marshes are wetlands dominated by herbaceous plants such as grasses, rushes and reeds. Saltmarshes ‘catch’ pollutants from human settlements downriver and stop them from entering the sea. Freshwater swamps form on the slow stretches of rivers or the edges of lakes. Migratory birds nest in saltmarshes before heading to sea. Famous marshes include the Everglades of Florida, the Mesopotamian Marshes of Iraq and the Okavango Delta.
Bogs are the remains of ancient glaciers which melted at the end of the Ice Age. Unlike swamps and marshes, they are found only inland in colder, northern climates. Rather than trees or grasses, bogs are home to peat, a thick, spongy soil created from ancient, decaying plant matter, which eventually turns into coal. The excess of peat stifles plant growth, meaning bogs are often acidic and low in oxygen. Bogs dominate regions of Ireland, Russia, Scandinavia and North America and take over ten thousand years to form.
Fens form from glaciers but, unlike bogs, are fed by rivers and are alkaline, not acidic. They host both peat deposits and grassy plants. From a distance, fens resemble low-lying meadows. If enough peat develops or it loses access to freshwater, a fen can turn into a bog.
‘Mire’ is another word for a peat wetland, like a fen or bog. Human activity threatens wetlands. Rising sea levels caused by climate change can flood coastal wetlands and destroy these valuable habitats. Since the Industrial Revolution, humans have drained wetlands for agriculture and urban development and dammed the rivers which feed them. The loss of wetlands threatens the species who live there and risks losing the protection they offer. Since 1900, half the world’s wetlands have disappeared.
Sources: National Geographic, The Wildlife Trust, WWF