Practice question

A fen is a peat-forming wetland supplied by groundwater or mineral-rich surface water in addition to precipitation. Water moving through soil and rock carries dissolved calcium, magnesium, bicarbonate, and other ions, making most fens less acidic and more nutrient-rich than rain-fed bogs. Some are neutral or alkaline, especially in limestone regions, although mildly acidic fens also occur; groundwater influence is more fundamental than a universally high pH. Sedges, grasses, brown mosses, and specialized flowering plants commonly dominate, and peat accumulates because saturation restricts oxygen and slows decomposition. Bogs are mainly ombrotrophic, receiving water from rain, and are usually acidic and nutrient-poor. Wetlands with mineral soil and trees are more commonly called swamps, while shallow rocky conditions do not define a fen. The keyed description combines the usual chemical tendency—alkaline conditions—with the causal hydrology—groundwater feeding. That water source explains the greater mineral availability, distinctive vegetation, and generally higher productivity of fens compared with bogs.