Figure 15. Great Dismal Swamp National Wildlife 

 Refuge, Virginia and North Carolina (from USFWS 

 1986b). 



Development and g eo graphy . Although 

 paleogeography of the Atlantic coast is still the sub- 

 ject of debate (e.g., Watts and Stuiver 1980; Bloom 

 1983), it is generally believed that the Dismal Swamp 

 probably first developed along coastal streams 

 1 1,000 to 12,000 years ago (Oaks and Coch 1973; 

 USFWS 1986b). Palynological evidence (Whitehead 

 1965) indicates that full-glacial boreal spruce-pine 

 forests were succeeded by pine-spruce forests and, 

 toward the end of the late-glacial, by northern 

 hardwood forests. During the early postglacial 

 period, the forests were dominated by hardwoods 

 that currently grow in the region. A variable cypress- 

 gum forest has characterized the Dismal Swamp for 

 the past 3500 years (Whitehead and Oaks 1979). The 

 wetland expanded along watercourses, and peat 

 accumulated until by 3,500 years B.R, peat had blan- 

 keted the present-day Dismal Swamp. Whitehead 

 (1965) and Whitehead and Oaks (1979) found that 

 cypress (Taxodium) and cedar pollens first appear in 

 the peat about 6,500 yrs B.P, increasing to 60% of 

 pollens by 3,000 yrs B.P Since then, cypress and 



cedar have comprised 40°/o-60% of the peat pollen 

 profile. (Chamaecyparis pollens were not counted 

 separately.) 



Climate, physio graphy, topo graphy, and 

 geology . Temperatures, precipitation patterns, and 

 humidity are similar to that of Dare County, North 

 Carolina (see Chapter 7). The Dismal Swamp lies on 

 the Atlantic Coastal Plain, between the Suffolk Scarp 

 and the Deep Creek Swale. Elevations range from 

 4.6 to 7.6 m. The topography slopes gently to the 

 east at the rate of 0.2 m/km (Carter 1987). 



The geologic formation most intimately as- 

 sociated with the Dismal Swamp water budget, 

 which accounts for the majority of water that upwells 

 in the swamp, is a shallow aquifer composed of coar- 

 sely-grained to finely-grained old marine sands 

 (Lichtlerand Walker 1979). Formerly termed the Nor- 

 folk Formation (now recognized as the Shirley and 

 Tabb Formations [Carter 1987]), this is a water-bear- 

 ing layer through which water moves laterally. 



Soils. The soils of the cedar swamps are 

 black, fine-grained, highly decomposed mucky 

 peats characterized by poor drainage and high 

 acidity, with mean annual soil temperatures between 

 15 and 22 °C. Undecomposed logs and stumps are 

 buried in the decomposed organic material at depths 

 ranging from a few centimeters to 1 .5 m (Lichter and 

 Walker 1979; Otte 1981). Permeability varies with 

 the composition of the subsoil. 



Hydrology . As the wetland district's 

 hydrological functions are interrelated, and data 

 restricted to the cedar stands are unavailable, infor- 

 mation on the water regime of the entire Dismal 

 Swamp (Lichtlerand Walker 1979; USFWS 1986b; R 

 Gammon, pers. comm.) is examined here. 



Inflow . Ground water (a major influence) 

 flows into the swamp from the west through perme- 

 able layers that interface with the shallow "Norfolk" 

 aquifer The average annual precipitation is 127 cm 

 (U.S. Weather Bureau 1926-1975, quoted in USFWS 

 1 986b). Surface water inflow from the west along the 

 Suffolk Scarp is a minor influence, with most of it 

 moving out rapidly through streams and ditches. 



Water loss . Evapotranspiration (the com- 

 bined effects of evaporation and transpiration) in 

 areas upstream (i.e., west) of the swamp severely 

 limits inflow during summer months despite high 

 rainfall. In the summer months, evapotranspiration 

 probably accounts for the biggest portion of water re- 

 moval from the swamp ecosystem. It exceeds rain- 

 fall during the growing season and causes a lowering 



20 



