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valley bog


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A mire community that develops in wet valley bottoms, valleys with some downstream impedance, or badly drained hollows. Many European valley mires have layers of charcoal in their stratigraphy below the peat, suggesting that fire may originally have initiated peat formation by creating a charcoal deposit that effectively seals off basal soils from water penetration and causes waterlogging. The groundwater is base-poor and conditions are acidic. This type of mire is flow-fed (rheotrophic), so technically it is a poor fen type of community rather than a true bog. The supply of nutrients is determined by the concentration of elements in the drainage water (which is usually low) and the rate of water flow through the system. The central part of the mire often has the fastest water flow and is hence less oligotrophic than the lateral parts of the mire. In extensive valley mires the acidic, lateral mire expanses may become elevated and ombrotrophic if rainfall is adequate. Compare blanket bog; ombrogenous bog; raised bog.

Subjects: Plant Sciences and Forestry — Ecology and Conservation.


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