Applied Wetlands Science - Chapter 1

Kent, Donald M. “Definition, Classification, and U.S. Regulation” Applied Wetlands Science and Technology Editor Donald M. Kent Boca Raton: CRC Press LLC,2001 CHAPTER 1 Definition, Classification, and U.S. Regulation Donald M. Kent CONTENTS Definition Classification Classification of Wetlands and Deepwater Habitats of the United States A Hydrogeomorphic Classification for Wetlands U.S. Regulation Regulating Agencies Army Corps of Engineers Environmental Protection Agency Fish and Wildlife Service National Resource Conservation Service National Marine Fisheries Service References DEFINITION Wetlands are defined directly or implicitly in a variety of ways. Several factors, including personal perspective, position in the landscape, and wetland diversity and function, contribute to the tractable nature of the definition. Each individual or group brings to the definition its own perspective based upon cumulative experience and personal needs (Figures 1 to 4). For example, the lay person asked to define wetlands may envision a deep-water marsh teeming with ©2001 CRC Press LLC ducks, or alternatively a dark swamp. To an engineer a wetland may be a place that will require a specialized construction design to accommodate poorly drained soils. The scientist likely has a functional perspective, defining a wetland as a place where anaerobic processes occur, and plants are adapted specially for living in saturated or inundated conditions. Finally, those charged with regulating wetland use are likely to have a structural perspective, defining wetlands by characteristic soil, hydrology, and plants so as to facilitate permit decision making. Figure 1 Salt marsh is an emergent, interdial estuarine wetland system characterized by persistent plant species such as cordgrass (Spartina alterniflora). Saltmarsh has a fringe geomorphic setting, and the water source and hydrodynamics are pre-dominantly surface or near surface bidirectional flows. Defining wetlands is further complicated by their position in the landscape. Wetlands are transitional habitats in the sense that they are neither terrestrial nor aquatic, but exhibit characteristics of both. Their boundaries are part of a continuum of physical and functional characters, and may expand or contract over time depend-ing upon factors such as average annual precipitation, evapotranspiration, and mod-ifications to the watershed. The transitional nature of wetland characteristics and the shifting of wetland boundaries renders precise identification of wetland boundaries difficult if not impossible. The diversity of wetland types also contributes to the tractable nature of the definition. Wetlands include such familiar habitats as marsh and swamp, as well as less familiar seasonal wetlands such as vernal pools and intermittent streams. They may be tidal or nontidal, saline or fresh, lotic or lentic, permanent or imper-manent. Vegetation may consist of herbaceous or woody species, or there may be no vegetation. ©2001 CRC Press LLC Figure 2 Figure 3 This marsh is an emergent, palustrine wetland with a depressional setting. It is subject to vertical fluctuations in water level, and derives its water from precipitation and groundwater discharge. Palustrine wetlands may also be wooded as illustrated by this hardwood swamp. Swamps frequently have a riverine setting and unidirectional, surface or near-surface flows. Wetlands also defy a unifying functional definition. Each wetland is unique with respect to its size, shape, hydrology, soils, vegetation, and its position in the land-scape. As such, wetlands exhibit a wide range of functional attributes, including provision of aquatic and wildlife habitat, retention of sediments and toxicants, flood ©2001 CRC Press LLC Figure 4 This vernal pool in California is inundated or saturated for a short time in early spring. It occurs in a depressional setting and is dependent upon precipitation for water. attenuation, nutrient metabolism, groundwater recharge, and production export. Individual wetlands may exhibit some of these attributes, all of these attributes, or in rare instances, none of these attributes. Moreover, individual wetlands of similar attributes are likely to provide functions to differing degrees. Despite the difficulty in singularly defining wetlands, several formal definitions have been proposed. The earliest definition was for managers and scientists, partic-ularly those concerned with waterfowl and wildlife (Shaw and Fredine, 1956). Largely a structural definition, it uses language understandable to the lay person. The term wetland … refers to lowlands covered with shallow and sometimes tempo-rary or intermittent waters. They are referred to by such names as marshes, swamps, bogs, wet meadows, potholes, sloughs, and river-overflow lands. Shallow lakes and ponds, usually with emergent vegetation as a conspicuous feature, are included in the definition, but the permanent waters of streams, reservoirs, and deep lakes are not included. Neither are water areas that are so temporary as to have little or no effect on the development of moist-soil vegetation. The definition established two parameters essential for a habitat to be a wetland: the presence of surface water and the development of moist-soil vegetation. At a workshop of the Canadian National Wetlands Working Group, 23 years later, a definition evolved that recognized a third parameter, hydric soils, and which noted the functional attributes of wetlands (Tarnocai, 1979). Furthermore, it expanded the previous definition of wetland to include not only those habitats with surface water but also those having saturated soils. ©2001 CRC Press LLC ... - tailieumienphi.vn