ABSTRACT
Freshwater wetlands are one of the most productive ecosystems in the world. Biogeochemical cycles in freshwater wetlands are regulated by external material inputs, hydrology, vegetative communities, physicochemical characteristics of soils, and associated internal processes. Marshes, swamps, bogs, and fens constitute broad categories, with each group exhibiting distinct differences with respect to their hydrology, vegetative communities, and soil types (see Chapter 3). For example, marshes (tidal and nontidal) are periodically saturated, ooded, or ponded with water and characterized by herbaceous (nonwoody) vegetation. Soils can be either mineral or organic. Swamps are fed primarily by surface inputs and are dominated by trees and shrubs or mangroves (some examples in the United States include bottomland hardwood forests, Okefenokee Swamp, Georgia; Great Dismal Swamp, Virginia). Soils in swamps can be either mineral or organic. Bogs are freshwater wetlands characterized by spongy peat deposits. Many of these systems receive rainwater as the main input source. Fens are groundwater-fed, peat-forming wetlands covered with grasses, sedges, reeds, and other plants. Biogeochemical differences and relative rates of many of the individual processes measured in these systems are discussed in various chapters of this book.
