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Question: What is the characteristics of peatland hydrology?

Answer: The hydrological functioning of peatlands varies depending on the season, the position in the
watershed and the state of drainage or degradation (Acreman and Holden, 2013). The large surface,
flat topography and water-holding capacity generally allows low lying peatlands to play a buffering role
in regional hydrology. Peatlands and other wetland types, including marshes and floodplain wetlands,
are often seen as ‘sponges’, delaying flood peaks and reducing their amplitude. During dry periods,
these wetlands may provide a source of water to the regional stream network. Less well known is the
potential for wetlands to enhance flooding. Though more common in headwater and upland rainfed
wetlands, this effect can happen in any peatland with a high water table already at holding capacity
before a storm. In this case, peatlands can be a source of overland flow.
Peatland hydrology, as well as much of its ecology, has been described according to a system with two
distinct layers: the ‘acrotelm’ and the ‘catotelm’ (Ingram, 1982; Clymo, 1984; Holden and Burt, 2003;
Morris et al., 2011). In this system, the catotelm is the permanently saturated lower portion of the peat
profile that underlies the acrotelm, a high-hydraulic conductivity ‘active’ layer. The catotelm is nearly
always anoxic with slow biogeochemical kinetics, while the acrotelm is aerobic (i.e. oxygen-containing)
during periods when the water table is deep (and possibly year-round depending on site conditions).
More recent conceptual modeling has found it beneficial to view to peatland biogeochemistry and
hydrological interactions in terms of ‘hot spots’. This conceptual model proposes greater degrees of
lateral and vertical variation than a simple boundary layer between catotelm and acrotelm. Hot spots
may occur at interfaces between different microtopographic units and may be responsible for the bulk
of a site’s CH4
emissions or aquatic biogeochemical processing.
Drained or agricultural peatlands have different hydrological functions, which are often governed
by changes in the peat’s physical properties (e.g. compaction) or by management history. Generally,
the drainage of these peatlands lowers the depth of the water table and allows greater infiltration
of precipitation. For flood management, however, this storage effect can be partially or totally
counteracted by the increased rate of drainage from tiled, channelized or otherwise managed systems.
The varying proportion of vegetation cover in all peatlands, particularly in agricultural settings, plays a
role in controlling the speed of overland flow. Variations in vegetation add another component to the
variability of the peatlands hydrological function.
Drainage also has critical, nearly irreversible, effects on peat structure and on the ecological services
provided by peatlands (Oleszczuk et al., 2008). The substantial drop in the water table that is required
for agricultural production (ranging from 0.4 metres for grasslands to 1.2 metres for crop production)
leads to a decline in soil moisture content and the contraction of peat volume, which is further
compounded by oxidation. This consolidation increases the specific density of the upper peat layers and
causes the soil surface to subside. These shifts in peat properties decrease its structural porosity and
hydraulic conductivity, which makes it difficult to carry out continued draingage in peatland landscape
(Pfadenhauer and Klötzli, 1996; Kechavarzi et al., 2010).

(Source: MITIGATION OF CLIMATE CHANGE IN AGRICULTURE SERIES 9 - Climate-responsible peatlands management (Food and Agriculture of United Nations), 29 Jan 2021)

Source Link: http://www.fao.org/3/a-i4029e.pdf