Marsh plants breathe through built-in snorkels running down their stems
Rooted in waterlogged mud with almost no oxygen, marsh plants such as cattails and sedges survive by piping air from their leaves down to their roots through internal channels. The wetlands they build rank among the most biologically productive places on Earth, soak up floods, and scrub pollutants from passing water.
A marsh is a wetland dominated by soft-stemmed plants, grasses, rushes and reeds, rather than trees. That distinguishes it from a swamp, which is wooded, and from a mire, which accumulates acidic peat. Where low shrubs creep in, the result is sometimes called a carr. Marsh water tends to be neutral to alkaline, unlike the acid conditions of a bog. The channels that let plants survive are called aerenchyma, and many species also spread and store food through underground rhizomes. Animals cope too: some fish and salamanders tolerate low oxygen indefinitely, while others gulp air.
Three main types occur worldwide. Salt marshes form along sheltered coasts in mid to high latitudes, typically in lagoons, estuaries or behind sand spits, wherever sediment piles up faster than the land subsides; salt-tolerant grasses dominate them. Freshwater tidal marshes feel the tides without the salt and host far greater diversity. Plain freshwater marshes are North America's most common wetland. They include vernal pools that dry out each summer, prized by amphibians such as the endangered gopher frog because fish cannot survive there to eat their eggs, and prairie potholes, glacier-carved hollows that fill each spring and shelter breeding waterfowl.
Marshes earn their keep. Their productivity supports fisheries, they trap sediment and absorb nutrients before water reaches the sea, and they store heavy rain and release it slowly, blunting floods. They hold about 0.1 percent of the carbon stored on land and buffer coasts against storm-driven tides.
They have also been drained on a vast scale. Embanked tidal marshes are called polders in Dutch, Marsch in northern Germany and fens in East Anglia. Some regions have lost 90 percent of their wetlands to farming or urban growth, and most natural marshes face rising seas, though restoration projects, including letting rivers flood in spring, are bringing some back.
Source: Marsh
