Preface

Peatlands are wetlands whose soil comprises the partially decomposed remains of plants that accumulate in a way that both responds to—and controls—the flux and storage of surface water and groundwater within peatlands and runoff to downstream ecosystems. Water tables are generally at or near the surface, at least for much of the year. As the largest global terrestrial store of carbon, peatlands strongly influence global climate.

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. Boreal and temperate bogs often have a sparse cover of stunted trees, whereas tropical systems can have a dense cover of large trees.

In contrast to bogs, 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 water received controls their plant community function and structure and, therefore, their soil properties and 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 have a more episodic water exchange, thus variable water table, that is more favorable for woody vegetation.

In peatlands, more recently formed—thus less decomposed—soils occur in the upper layers; these newer soils can have extremely high porosity (≤ 95 percent) and are typically more permeable (saturated hydraulic conductivity up to 10 to 1000 m d^-1), whereas soils deeper than 0.3 to 0.5 m generally have low hydraulic conductivity (≤ 0.5 m d^-1). Consequently, the transmissivity feedback in peatlands exacerbates surface and groundwater flows when the water table is particularly high.

Understanding the hydrology and water quality of peatlands is key to effective land management where peatlands are common on the landscape.