Peat formation

The habitat requirements for peat initiation and accumulation are similar in every geographical location (waterlogging, low pH, low nutrient availability, low oxygen supply, reduced decomposition rate) but the physical and chemical characteristics differ according to specific site characteristics of landscape area and topography, climate, water depth and flow, nutrient availability and biogeographical availability of plant species. 

Peat formation is the result of incomplete decomposition of the remains of plants growing in waterlogged conditions. This may happen in standing water (lakes or margins of slow flowing rivers) or under consistently high rainfall (upland or mountain regions). As a result, partially decomposed plant remains accumulate and become compacted, forming peat that changes the substrate chemical and physical properties leading to a succession of plant communities. 

This process is referred to as the hydrosere that begins classically in open water and proceeds through fen stages that are influenced by nutrient-rich ground water (and rainfall) to bog that receives nutrients and water supply only from rainfall.

The hydrosere

The hydrosere is a continuum of vegetation types that replace each other as habitat succession proceeds from an initial phase (open water or other) to bog in response to changes in water depth, trophic status and plant communities.

The hydrosere may be initiated in waters of any trophic status from oligotrophic to eutrophic followed by infilling of the water body by sediments of either external (allochthonous) or internal (autochthonous) origin. Hydroseral succession may also commence in response to excessively high rainfall on landscapes of mineral soil or rock.

The processes involved in hydroseral succession can be maintained under two distinctly different water supply regimes, namely, geogenous or ground water, which is enriched with dissolved nutrients and ombrogenous water from aerial precipitation. The terms ombrotrophic and rheotrophic are used to differentiate between mires formed under the influence of either geogenous or topogenous waters.

There is a large range of rheophilous mires that have developed because of differences in water chemistry, depth and flow rate, forming a continuum from highly calcareous mires with no or little peat to nutrient deficient ones in which peat accumulation starts to divert geogenous water away, making the mires dependent increasingly on ombrogenous water (rainfall). This intermediate stage in the hydrosere as acidification commences is often referred to as transition mire and is characterized by the presence of species of both rheotrophic and ombrotrophic mire the roots of which occupy different depths below the peat surface.

The terminal acidification stage of the hydrosere is characterized by ombrotrophic mires the vegetation of which is completely dependent on an ombrogenous water and nutrient supply. Their substrate is not only acidic but contains by-products of anaerobic decomposition of plant material that are toxic to many plants and hence biodiversity is reduced compared to rheotrophic mires.

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