What distinguishes marshes, swamps, bogs, and fens
Wetlands are classified mainly by their water source and dominant vegetation. Marshes are dominated by soft-stemmed herbaceous plants such as reeds, cattails, and grasses, and are fed by surface or ground water with relatively high nutrient levels. Swamps are dominated by woody plants, including trees and shrubs, and are common along slow rivers and floodplains.
Bogs and fens are both peatlands, meaning they accumulate partially decayed plant matter. The key difference is water source: bogs receive water almost entirely from precipitation, making them acidic and nutrient-poor, while fens are fed by groundwater that carries minerals, making them less acidic and more nutrient-rich.
Why wetland type matters for ecology
Water chemistry follows directly from these distinctions. The acidic, low-oxygen conditions of bogs slow decomposition and favor specialists like sphagnum moss and carnivorous plants, while the mineral-rich water of fens supports a wider range of sedges and wildflowers.
All wetland types provide flood buffering, water filtration, carbon storage, and habitat. Peatlands in particular store disproportionately large amounts of carbon relative to their area, so their preservation is significant for climate as well as biodiversity.