Short answers, pulled from the story.
In ecology, a marsh is a wetland dominated by herbaceous plants rather than woody plants. It is often found at the edges of lakes and streams, forming a transition between aquatic and terrestrial ecosystems, and is typically dominated by grasses, rushes, or reeds.
A marsh is dominated by herbaceous plants such as grasses, rushes, and reeds, while a swamp is dominated by trees. A mire is a wetland that has accumulated deposits of acidic peat, whereas the pH in marshes tends to be neutral to alkaline.
The three main types of marsh are salt marshes, freshwater tidal marshes, and freshwater marshes. They differ mainly by location and salinity, and each can be found worldwide with a different set of organisms.
Marsh plants survive in wet mud with low oxygen through aerenchyma, channels within the stem that move air from the leaves into the rooting zone. They also tend to have rhizomes for underground storage and reproduction, with common examples including cattails, sedges, papyrus, and sawgrass.
Marshes have some of the highest levels of biological production in the world, supporting fisheries and habitats for invertebrates, fish, amphibians, waterfowl, and aquatic mammals. They also filter pollutants and sediment from water, absorb water during heavy rainfall to reduce flooding, and contain 0.1% of global sequestered terrestrial carbon.
A vernal pool is a type of freshwater marsh found seasonally in shallow depressions, often covered in shallow water but dry in summer and fall. Many amphibian species, including the endangered gopher frog, depend on vernal pools for spring breeding because the ponds are free of fish that eat amphibian eggs and young.
Embanked and artificially drained tidal marshlands are usually known by the Dutch name polders. They are called Marschland, Marsch, or marsk in Northern Germany and Scandinavia, marais maritime in France, marine clay districts in the Netherlands and Belgium, and Fens in East Anglia.