Marshes - Non-wooded Wetlands

Abstract

Freshwater marshes occur on nearly all continents and include 20–25% of all natural freshwater wetlands globally. Freshwater marshes include all nonforested wetlands except peatlands (e.g., bogs, fens, and mires) and shallow open water wetlands, and are dominated by herbaceous plants, particularly grasses, sedges, and rushes. Freshwater marsh is used in its broadest sense here and includes low, poorly drained areas such as wet meadows, wet prairies as well as deeper marshes dominated by emergent, submergent, rooted floating-leaved, and floating plants. Freshwater marshes include (a) riverine marshes transitional between rivers and uplands; (b) lacustrine marshes transitional between lakes and uplands; (c) palustrine marshes in depressions, seepage areas on hillslopes, and on waterlogged soils on low, flat areas in the landscape not connected to lakes or rivers such as prairie potholes and playas; and (d) freshwater tidal marshes. Freshwater marshes are among the most productive ecosystems on Earth, with mean primary production rates between 2000 and 2500 g m−2 year in permanent and semipermanent marshes but lower in seasonally flooded marshes. Plant production supports highly diverse plant, animal, and microbial communities that are linked in complex food webs. Plant communities often correlate with depth and duration of flooding and may extend from uplands into lakes or rivers to a depth of 2 m. Plant zones include wet prairies, wet meadows, shallow and deep emergent zones, and submergent, floating, and rooted floating-leaved plant zones. Not all marshes have all zones. Some may consist of a single plant zone (e.g., wet meadows in shallow depressions, emergent zones in steep-sided lakes and rivers). Marsh plants are represented by macrophytes (e.g., flowering monocots and dicots, ferns, mosses, filamentous macroalgae), phytoplankton (algae in the water), and benthic algae (algae on substrates, i.e., periphyton). Animal biodiversity includes high species richness of invertebrates, fish, amphibians, reptiles, mammals, and birds. Marshes provide many ecosystem services including water storage, flood protection, and water-quality renovation. Marshes produce many products valued by humans, including edible plants such as wild rice and cranberries, fish, shellfish, waterfowl, crocodilians, turtles, and mammals, which are eaten or produce valuable fur, skins, and other products. They also support a multimillion dollar business in ecotourism.