Function of wetlands
• Hydrologic Flux and Storage
• Biogeochemical Cycling and Storage
• Biological Productivity
• Community Structure and Wildlife Support
Hydrologic Flux and Storage
Wetlands play an important role in regulating the movement of water within watersheds as well as in the global water cycle (Richardson 1994; Mitsch and Gosselink 1993). Wetlands are characterized by water saturation in the root zone, at, or above the soil surface, for a certain period of time during the year. This fluctuation of the water table above the soil surface is unique to each wetland type.
Wetlands store precipitation and then slowly release the water into surface water resources, ground water, and the atmosphere. Wetland types differ in this capacity based on a number of physical and biological characteristics, including: landscape position, soil saturation, degree of decomposition of the organic soils, vegetation density and type of vegetation (Taylor et al. 1990).
Ground water recharge
Wetlands help to maintain the level of the water table and exert control on the hydraulic head (O’Brien 1988; Winter 1988). There are many factors which determines the extent of ground water recharge by a wetland such as soil, vegetation, site, perimeter to volume ratio, and water table gradient (Carter and Novitzki 1988; Weller 1981). Ground water recharge occurs through mineral soils found mainly around the edges of wetlands (Verry and Timmons 1982). Most wetlands consist of relatively impermeable soil. Wetlands having high perimeter to volume ratio specially small wetlands have high surface area through which water can infiltrate into the soil(Weller 1981). It has discovered that ground water recharge is up to 20% of wetland volume per season (Weller 1981).
Climate control is another hydrologic function of wetlands. According toRichardson and McCarthy (1994) many wetlands return almost two-thirds of their annual water inputs to the atmosphere through evapotranspiration. Wetlands play an important role to moderate temperature extremes in adjacent uplands (Brinson 1993).
The oxidation-reduction (redox) conditions are controlled by the fluctuating water levels of wetland. These redox conditions play a key role in nutrient cycling, availability, and export; pH; vegetation composition; sediment and organic matter accumulation; decomposition and export; and metal availability and export.
Microbial and chemical processes occur in dry soil using oxygen as the electron acceptor. When wetland soil is saturated with water, microbial respiration and biological and chemical reactions consume available oxygen. This shifts the soil from an aerobic to an anaerobic condition. Acceptors other than oxygen are used for the reactions when the conditions become reduced. These acceptor are nitrate, ferric iron, manganese, sulfate, and organic compounds.
Hydrologic flux and life support
Changes in frequency, duration, and timing of hydroperiod may impact spawning, migration, species composition, and food chain support of the wetland and associated downstream systems (Crance 1988). Normal hydrologic flux supports exchange of nutrients, detritus, and passage of aquatic life between systems.
Values of wetlands as a result of the functions of hydrologic flux and storage include: water quality, water supply, flood control, erosion control, wildlife support , recreation, culture, and commercial benefits.