La Boganii — Bogs, fens and peatlands: how each | la-boganii.com
Four wetland types, one deciding variable — where the water comes from — and a table that sorts them by pH, nutrients and plants.
Start with the water budget. A bog is ombrotrophic: rain only, no streams in, no springs. A fen is minerotrophic: groundwater arrives carrying dissolved minerals. Swamps and marshes are also minerotrophic, but their water is surface flooding and nutrient-rich runoff rather than the slow seepage that feeds a fen.
Acidity sorts them next. Sphagnum bog pools measure pH 3.0-4.5; rich fen water sits near pH 6.0-7.5. Swamps and marshes, flushed with mineral-rich surface water, sit near neutral and carry far more nutrients than either peat type.
Plants finish the identification. Bogs carry a Sphagnum carpet with heather and cotton-grass. Fens carry sedges, reeds and brown mosses. Swamps are wooded — trees and shrubs standing in water. Marshes are open grass-and-sedge stands, usually on mineral soil with little or no peat.
On narrow screens, swipe or scroll the plate sideways.
Worked example, bog: the blanket bogs of western Ireland and Scotland, where yearly rainfall around 1,000 mm or more with low evaporation lets peat spread across whole hillsides; the same formation covers Tierra del Fuego.
Worked example, fen: a valley-bottom rich fen where springs keep the water near pH 6.0-7.5, sedges dominate, and peat builds slowly under the sedge litter — the mirror image of the rain-fed dome uphill.
Worked example, swamp and marsh: a wooded swamp reads as wet forest with standing water between trunks, while a marsh reads as a flooded meadow; neither carries the deep, acid, Sphagnum-built peat that defines a bog. To confirm any of the four on the ground, run the six-step check at /identify-a-bog-field-steps, and for the peat beneath them see /peat-depth-age-carbon.
Further reading