National Water Summary-Wetland Resources 387 Virginia Wetland Resources Wetlands cover about 4 percent of Virginia (Dahl, 1990). These ers, 1979). The distribution of wetlands and deepwater habitats in wetlands support rich biotic conununities in freshwater, saltwater, Virginia is shown in figure 2A; only wetlands are discussed herein. and brackish-water settings across the State. Well-known Virginia Wetlands can be vegetated or nonvegetated and are classified wetlands include the extensive estuarine marshes behind the coastal on the basis of their hydrology, vegetation, and substrate. In this barrier islands and the forested wetlands along tidal rivers and in summary, wetlands are classified according to the system proposed the Great Dismal Swamp (fig. l). by Cowardin and others (1979), which is used by the .S. Fish and Wetlands have many chemical, physical, and biological func­ Wildlife Service (FWS) to map and inventory the Nation's wetlands. tions. They benefit entire ecosystems, including resident human At the most general level of the classification system, wetlands are populations (Hershner, 1992). Wetlands trap waterborne sediments grouped into five ecological systems: Palustrine, Lacustrine, Riv­ and retain nutrients and toxic chemicals by filtering them out of erine, Estuarine, and Marine. The Palustrine System includes only inflowing water and storing or transforming them. Wetlands al o wetlands, whereas the other sy terns comprise wetlands and can recharge ground-water supplies or serve a,; points of ground­ deepwater habitats. Wetlands of the systems that occur in Vuginia water discharge to the surface. Coastal-zone and flood-plain wet­ are described below. land mitigate the effects of flooding caused by tides and runoff by reducing flow velocity, storing water temporarily, and releasing it gradually. Vegetation in riparian wetlands maintains stream chan­ System Wetland description nel by stabilizing the banks, and vegetated tidal wetlands act a Palustrine .................. Nontidal and tidal-freshwater wetlands in which buffers against storm tides and waves, thus impeding erosion. One vegetation is predominantly trees (forested wet­ lands); shrubs (scrub-shrub wetlands); persistent of the most important functions of wetlands is to provide habitat or nonpersistent emergent, erect, rooted herba­ for waterfowl, terrestrial and aquatic animals, and a wide variety of ceous plants (persistent- and nonpersistent­ plant life. Wetlands in Virginia provide food, shelter, and resting emergent wetlands); or submersed and (or) places for migratory birds, as well as breeding areas and nurseries floating plants (aquatic beds). Also, intermit­ for many animals, including tho e of particular economic intere t tently to permanently flooded open-water bod­ ies of less than 20 acres in which water is less in Vrrginia uch as blue crabs, muskrat, fish, ducks, and geese. Many than 6.6 feet deep. rare and endangered plant species are adapted to hydrologic condi­ Lacustrine ................. Nontidal and tidal-freshwater wetlands within an tions present only in wetlands. intermittently to permanently flooded lake or Virginia's wetlands have considerable esthetic, historic, archeo­ reservoir larger than 20 acres and (or) deeper logical, recreational, and economic value (Hershner, 1992). Humans than 6.6 feet. Vegetation, when present, is pre­ dominantly non persistent emergent plants (non­ have inhabited the coastal wetlands of u ginia for thousands of persistent-emergent wetlands), or submersed years, and unique cultures have developed there. Wetlands provide and (or) floating plants (aquatic beds). or both. outdoor educational and recreational opportunities such as Riverine ..................... Nontidal and tidal-freshwater wetlands within a birdwatching, hilting, and canoeing. They also support the hunting, channel. Vegetation, when present, is same as fur trapping, commercial and sport fishing, lumbering, and tourist in the lacustrine System. industries, which benefit the economy of the State. Estuarine ................... Tidal wetlands in low-wave-energy environments where the salinity of the water is greater than 0.5 part per thousand (ppt) and is variable owing to TYPES AND DISTRIBUTION evaporation and the mixing of seawater and freshwater. Wetlands are lands transitional between terrestrial and deep­ Marine ....................... Tidal w etlands that are exposed to waves and cur- water habitats where the water table usually is at or near the land rents of the open ocean and to water having a surface or the land is covered by shallow water (Coward in and oth- salinity greater than 30 ppt. Palustrine wetlands comprise about 72 percent of the wetland area of Virginia (Tiner and Finn, 1986). Estuarine wetlands com­ prise about 23 percent of the State's wetlands. Lacustrine wetlands in freshwater ponds comprise mo t of the remaining 5 percent. Only a few hundred acres of marine and riverine wetlands exist in Vir­ ginia. Palustrine forested wetlands (swamps) are the most abundant type of wetland in Virginia, accounting for about 60 percent of the total wetland area in the State. Estuarine emergent wetlands (tidal marshe ) are the second-most abundant type of wetland, compris­ ing about 8 percent of the wetlands in the State (Tiner and Finn, 1986). Virginia has many different types of wetlands. Salt marshes include the extensive estuarine wetlands along the Chesapeake Bay that are characterized by vegetation tolerant of brackish to salty water. Other tidal marshes include estuarine wetlands located along Figure 1. Wetlands in the Great D ismal Swamp, a freshwater parts of tidal rivers. Interdunal swales are topographic palustrine forested wetland. (Photograph by Virginia depressions among sand dunes on the Atlantic coast that contain Carter, U.S. Geological Survey.) palustrine emergent or scrub-shrub wetlands. Virginia's Atlantic 388 National Water Summary-Wetland Resources: STATE SUMMARIES white cedar swamps, red spruce swamps, and cypress-tupelo supplies adequate moisture for wetland formation and maintenance swamps and its nontidal flood-plain forests are palustrine forested and ranges statewide from 36 to 52 inches per year (Prugh and Scott, wetlands that have seasonally occurring standing water and flood­ 1986). Precipitation does not have a strong seasonal pattern during tolerant trees. Pocosins are palustrine scrub-shrub wetlands that are the year, but 80 to 85 percent of evaporation from open bodies of slightly elevated above the surrounding landscape and have flat to­ water occurs from April to October. That period coincides with the pography and poor natural drainage. Vrrginia 's bogs, fens, and wet higher transpiration rates of the growing season. meadows are palustrine emergent wetlands that are often underlain Annual and seasonal fluctuations in local precipitation and by organic soi ls. The presence and composition of plant communi­ evapotranspiration rates combine with local differences in geology, ties in the wetlands of Virginia are determined by factors such as topography, and soil characteristics to create short- or long-term the extent and duration of flooding, climate, type of soil, and ground­ changes in the interactions of ground water and surface water in and surface-water chemistry. wetlands. T hese changes can result in alternating flooded and dry About 72 percent of the wetland area in Vrrginia, including all conditions, especially in small wetlands (Winter, 1992; Phillips and the estuarine wetlands and most of the large nontidal wetlands, is Shedlock, 1993). Additionally, larger wetlands (tidal and nontidal) in the Coastal Plain (fig. 2A and 2R) (liner and Finn, 1986). Ex­ can interact with regional ground-water flow systems. In tidal wet­ tensive estuarine wetlands have developed in low-lying areas along lands, a major source of water is tidal inundation. Overland runoff the shores of the Chesapeake Bay and its tributaries and behind the and ground-water discharge can be important secondary sources. barrier beaches of the Atlantic coast. Palustrine wetlands are dis­ The major sources of water in nontidal wetlands are precipitation tributed throughout the State and are located primarily in bottom and ground-water discharge. lands and in flood plains along stream channels, especially in head­ Virginia includes five physiographic provinces: the Coastal water areas. About 22 percent of the wetlands in Virginia are in the Plain, Piedmont, Blue Ridge, Valley and Ridge, and Appalachian Piedmont, and most of the remaining wetland area is in the Appa­ Plateaus (fig. 2B ). Each province is characterized by geologic fea­ lachian Plateaus (Tiner and Finn, 1986; Harlow and LeCain, 1991). tures, landforms, and soils that directly affect the hydrology of wetlands. HYDROLOGIC SETTING Coastal Plain. - The Coastal Plain is relatively flat, rising from below sea level to about 50 feet above sea level on the Delmarva Virginia's wetlands (fig. 3A-3C) are formed and maintained Peninsula cast of the Chesapeake Bay and to about 200 feet above by water supplied by precipitation, overland runoff from precipita­ sea level on the upper Coastal Plain west of the Chesapeake Bay. tion, local and regional ground-water flow, and tides. Precipitation This province is underlain by an extensive and locally complex B Piedmont {f' Province Blue Ridge Pf"ovince A WETLANDS AND DEEPWATER HABITATS Distribution of wetl•nds •nd deepwater habibts- 0 25 50 M ILES This map shows the approximate distribution of large wetlands in the State. Because