Among wetland types, peatlands are characterized by permanently waterlogged soils, which determine biogeochemistry, vegetation composition, microbiological processes and slow decomposition rates, and make them to effective carbon sinks and stores.

Fens, i.e. ground- and surface water-fed peatlands, occur from the Arctic to the Tropics and from the high mountains to the sea. They exhibit a large ecological diversity, from oligotrophic to highly eutrophic and from slightly acidic to strongly calcareous and often have a high and special species richness. However, because of increased nutrient availability, they are also often strongly degraded by drainage and agricultural use.