Peatlands are wetlands with soil comprised of undecomposed remains of plants that accumulate in such a way that both responds to and controls the flux and storage of surface water and groundwater, as well as controlling runoff to downstream ecosystems. Water tables are generally at or near the surface for much, or all, of the year.
Peatlands strongly influence global climate because they are the largest global terrestrial store of carbon.
Depending on the setting, peatlands develop into distinct forms that peatland scientists generally categorize as bogs, fens, and swamps with peat soils. Bogs have accumulated sufficient peat depth, mostly due to the abundance of Sphagnum mosses, that they become topographically isolated and receive water only via precipitation, thus shed surface water and groundwater. Bogs can have a typically sparse cover of stunted trees. Fens and peat swamps generally receive water and constituent dissolved ions from adjacent mineral terrains, although flow directions may reverse. As with bogs, the quantity and quality of incoming water controls the function and structure of their plant community and, therefore, their soil properties including the ability to store and transmit groundwater. Fens generally have a steadier supply of water than swamps, and thus a more stable water table that favors sedges and brown mosses, and sometimes trees. Swamps typically experience episodic water exchange; thus, their water table varies, which is more favorable for woody vegetation.
In peatlands, more recently formed, less decomposed soils occur in the upper layers – these newer soils can have extremely high porosity (≤95%) and are typically more permeable (saturated hydraulic conductivity up to 10-1000 m/d), whereas soils deeper than 0.3 – 0.5 m generally have low hydraulic conductivity (≤0.5 m/d). Consequently, there is transmissivity feedback that exacerbates surface and groundwater flows when the water table is particularly high.
Understanding the hydrology and water quality is key to effective land management where peatlands are common on the landscape.