acrotelm

Acrotelm refers to the upper, dynamic portion of a peatland peat profile. It is the layer that remains actively involved in water exchange, oxidation-reduction processes, and biological activity, lying above the more permanently saturated catotelm. The term is used in peatland ecology and hydrology to distinguish the biologically active zone from deeper, more stable peat.

Composition and structure: The acrotelm includes the surface vegetation, such as Sphagnum moss, along with the upper peat layers that are repeatedly drained and rewet by rainfall, evapotranspiration, and capillary rise. It contains recently deposited litter, root networks of vascular plants, and microtopographic features that create variable pore spaces. Its porosity and hydraulic conductivity are higher than in the catotelm, allowing rapid drainage when the water table falls and quick rewetting after rain. The thickness of the acrotelm varies widely, commonly ranging from a few tens of centimeters to about a meter, depending on hydrology, peat formation history, and vegetation.

Hydrology and biogeochemical processes: Water table fluctuations within the acrotelm control oxygen availability and redox conditions, influencing decomposition rates and gas exchange. In wetter periods, the acrotelm becomes more reduced and aerobic decomposition slows; in drier periods, oxidation increases and decomposition accelerates. Although most methane production occurs in deeper, more anoxic zones, the acrotelm contributes to carbon dioxide and methane fluxes through intermittent aeration and drainage. The boundary with the catotelm marks a shift to more consistently saturated, slower-decomposing peat.

Ecological and climatic significance: The acrotelm is central to peatland carbon balance, hydrology, and vegetation dynamics. Changes in hydrology from drainage, climate warming, or land use can alter the depth and function of the acrotelm, potentially affecting peat formation and carbon losses from peat soils.