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For botanists and ecologists the term peatland is technically a more universal term for any terrain dominated by peat to a depth of 30–40 cm (12–16 in), even if it has been completely drained (i.e., a peatland can be dry, but a mire by definition must be wet). Fens and bogs are two types of mires, bogs being situated higher than the surrounding landscape on a domed-shaped landform and obtaining most of their water from rainfall (i.e., are ombrotrophic) while fens are located on slopes, flats, or depressions and get theirs from both rainfall and surface water.
Also, while a bog is always acidic and nutrient-poor, a fen may be either acidic or alkaline, and either nutrient-poor or nutrient-rich. A mire is distinguished from a swamp by its lack of a forest canopy (though some bogs may support limited tree or bush growth, mires are dominated by grass and mosses), and from a marsh by its water nutrients and distribution (marshes are characterized by nutrient-rich stagnant or slow-moving waters; mire waters are located mostly below the soil surface level) as well as its plant life (marsh plants are generally submerged or floating-leaved; those in a mire are not).:p.13
Because mires rely on rainwater for moisture, they are usually deficient in both oxygen and phosphorus, though they may vary widely with regard to nitrogen.:p.14 These things mean that mires are a kind of "...living relic... [A] living skin on an ancient body" in which successive layers of regular plant growth and decay are preserved stratigraphically with a quality of preservation unknown in other wetland environments.
The term quagmire is a variant term for a mire, the prefix quag- having been variously written as qua-, quab-, quad-, quake-, qual-, quave-, and quaw- in the 16th and 17th centuries, and afterwards the prefixes bob-, gog-, and wag- having also been used in the same way. The relationship between these terms is not linguistically clear though they may all have been an attempt to express the same general idea of shaky, wet, unsteady ground which could not support the weight of a man or large animal and was therefore dangerous to enter and difficult to leave.