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Arid Wetlands and Riparian AreasThe desert oasis, made famous in movies, clearly shows the contrast between its productivity and high value and that of its dry surroundings. Wetlands and riparian soils are extremely important in arid lands and to the management of the surrounding non-wetland soil. The boundary between wetland and non-wetland is most clear in desert environments and its identification less difficult than in more humid areas with less contrast. Wetland is defined as an area of shallow water or saturated soil with vegetation adapted to wet conditions. Riparian areas are ecosystems where soil and soil moisture are affected by adjacent rivers and streams. Riparian ecosystems are highly productive because great amounts of energy and materials converge and pass through them (Mitsch & Gosselink, 1993). In spite of their importance, wetlands and riparian areas are often underestimated because their small size or narrow, linear shape makes them difficult to inventory and map. As a result they usually do not receive adequate attention when planning and implementing development activities. This has serious implications both in terms of lost economic opportunities and maintenance of biodiversity. Threats to arid wetlands and riparian areas are many. Urban development and building on flood plains lead to expensive flood control measures, such as concrete canals, to protect property owners' investments from flooding. Watershed degradation that increases runoff, through such actions as overgrazing, causes abnormal peak flows that incise channels and cause lateral gully erosion. The erosion and lower water tables degrade the habitat. Large dams, especially for irrigation development, can cause desertification. Upstream they flood productive habitats and soils. Down stream they reduce flooding and stream flows, reduce aquifer recharge, and cause lower water tables. Vegetation that depends on this water disappears leaving a more desert like population of plant and animals (Johnson & Simpson, 1988). For example, dam construction on the Senegal-Bafing River of West Africa directly caused the desertification of soil. The reduced flooding changed the soil classification of some riparian soils from Alfisols to Aridisols (USDA system). Salinization of irrigated riparian soils is another common example of desertification. ReferencesJohnson, R.R. and J.M. Simpson (1988). Desertification of wet riparian ecosystems in arid regions of the North American Southwest. pp. 1383-1393. In Arid Lands Today and Tomorrow, eds. E.E. Whitehead, C.F. Hutchinson, B.N. Timmermann, and R.G. Varady. Boulder Colo.: Westview Press. 1435 p. Mitsch, W.J. and J.G. Gosselink (1993). Wetlands. New York: Van Nostrand Reinhold. 722 p. Text by Joe Tabor |
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URL:http://cals.arizona.edu/OALS/soils/aridwetlands.html
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