Many, many years ago I entered graduate school at the Yale School of Forestry and Environmental Studies in New Haven, CT. My graduate interests lay primarily in water resources, so I searched that first semester for a lead professor/advisor in that vast field – and, due to recent retirements, found none.
As luck would have it, a Ph.D. candidate hosted a course in basic wetland hydrology 101 that fall. He was young, energetic, no nonsense kind of person, a stickler for getting out in the field and measuring things like water flow, water inputs, outputs and what was going on underneath our feet and the wet soils he was interested in. He took us to interesting places called bogs, fens, and cedar swamps requiring hip boots. We saw great swamp trees, like tupelos or black gum. We brought back funny looking, stained sketches of bogs and fens, with arrows showing what we thought was the direction of water flow pointing in various directions. I learned that a fen was a kind of boggy wetland where surface and/or ground water flowed through, introducing minerals and oxygenated conditions and thus making a fen somewhat less mineral impoverished than a bog lacking such through flow.