Bogs, marshes and fens

Bogs are a sub-category of ‘wetlands’ a term used for a wide variety of landscapes that are either permanently or seasonally saturated with water. There are many types of bogs, including raised bogs, fens and transitional types. These types are distinguished by their different formation processes.

Topogenous bogs

‘Topogenous bogs’ include wet meadows, fens or marshes. These are formed under the influence of groundwater in low-lying areas. Plants that grow on the edge of or in the open water of these bogs, die and disappear below the water. As there is very little oxygen here they do not fully decay and over time, as the dead plant material accumulates, the open water is replaced by peat.

Raised bogs -Formation

Raised bogs, in which most bog bodies are found, are of a different nature. They are a dead, water-saturated mass of peat that can be several metres deep. These bogs originate in a period of wet and cool climate when water tables rise. As a result, various bog and peat mosses, all of which belong to the moss genus Sphagnum, may start growing. Sphagnum moss produces and tolerates acid. This makes the environment increasingly acidic and poor in nutrients. Other plants are not tolerant to acid and they die, eventually only leaving bog mosses and a few tolerant plants. The mosses grow each year whilst dead plant material does not decay below the living surface.

Over time the link with groundwater is severed and the bog survives on rainwater, air and minerals from the atmosphere. To survive without groundwater Sphagnum mosses have the ability to absorb and store rainwater. This ability, in combination with their dense growth in a large network of induvial plants means they act a bit like a sponge, holding a big water bubble. Thus, the bog grows upwards and spreads across the landscape over time. Eventually, the surface of the bog may be raised above the rest of the landscape giving this type of bog its name: ‘raised bog’. Yet what makes these bogs such good environments for the preservation of organic materials like human bodies? Click here to find out.