Marshes are generally treeless patches of land characterized by grasses, reeds and cattails and tend to be very lush ecosystems that sustain a wide variety of both plants and animals. Marshes usually exist in the shallows of nearby bodies of fresh water, such as lakes and rivers, or near the ocean, forming saltwater marshes.
The reason they sustain such a diversity of life is that water moving through the marshes typically replenishes the supply of oxygen available to native plant life, which in turn supports animals.
Bogs are wetlands characterized by watery masses of peat below surface level. Peat is partly alive and partly decomposed biomass formed over time by the plants that live on the surface of the bog, such as sphagnum mosses, shrubs and conifers. Bogs are also relatively acidic compared to other wetlands.
Bogs support a lesser variety of life than marshes because water doesn't move through them quickly enough to sustain high levels of oxygen in the water and because of the acidity of the environment. That doesn't mean bogs are barren, however; a number plants and animals have adapted to the bog environment.
Both marshes and bogs are threatened by human activities. For example, Louisiana has lost about 1,500 square miles of saltwater marshes due to levee building and other development since 1930. In places such as the British Isles, Scandinavia and Russia, peat is harvested from bogs for fuel. By one estimate, as much as 90 percent of bogs in the United Kingdom have been damaged or destroyed.
