Coastal Plain Depression Wetlands
This diverse group of poorly-drained basin wetlands is characteristic of flat Coastal Plain terraces with fluctuating, seasonally perched water tables. Similar wetlands are scattered throughout the mid-Atlantic Coastal Plain. The best-documented examples of this group in Virginia are the Grafton Ponds, located on The Peninsula in York County, but other sizeable complexes occur on Coastal Plain terraces in Dinwiddie, Surry, Isle of Wight, Gloucester, and Matthews Counties. Also included are the seasonally exposed shores of Lake Drummond, a 1,287 ha (3,180 ac) natural basin in the Great Dismal Swamp. South of the James River, two community types in this group extend into the eastern Piedmont, where they are associated with hardpan soils. Most of these wetlands are seasonally flooded and are believed to be sinkhole features that formed through dissolution of underlying carbonate-rich, shell marl deposits. The marl deposits are too deep to influence soil or water chemistry of the depressions, which are strongly acidic in most examples. A few depressions in extreme southeastern Virginia appear to have originated from deep peat burn-outs. Although the term "vernal pond" has been applied to some of the communities in this group, that name is rather restrictive and is a poor descriptor of the more extensive occurrences.
Vegetation in this group varies from nearly forested to entirely herbaceous, representing a sizeable number of distinct community types. Depth and duration of seasonal inundation are apparently the most important factors influencing community composition and the degree to which woody species become established. Dry-season fires in adjacent uplands may spread into ponds and may be another factor limiting the invasion of woody species, although fire frequencies throughout the region have been much reduced in recent decades. Typical trees occurring in wooded ponds are red maple (Acer rubrum), sweetgum (Liquidambar styraciflua), swamp tupelo (Nyssa biflora), blackgum (Nyssa sylvatica), willow oak (Quercus phellos), overcup oak (Quercus lyrata), and bald cypress (Taxodium distichum). Shrubs that dominate some ponds include buttonbush (Cephalanthus occidentalis), swamp loosestrife (Decodon verticillatus), common persimmon (Diospyros virginiana), and fetterbush (Eubotrys racemosa). Herbs characteristic of these communities are well adapted to long periods of submersion. Included are southern waxy sedge (Carex glaucescens), cypress-swamp sedge (Carex joorii), Walter's sedge (Carex striata var. brevis), long-tubercled spikerush (Eleocharis tuberculosa), square-stem spikerush (Eleocharis quadrangulata), creeping rush (Juncus repens), narrow-leaved seedbox (Ludwigia linearis), globe-fruited seedbox (Ludwigia sphaerocarpa), tall flat panic grass (Coleataenia rigidula ssp. rigidula), warty panic grass (Panicum verrucosum), mermaid-weeds (Proserpinaca palustris and Proserpinaca pectinata), short-bristled horned beaksedge (Rhynchospora corniculata), narrow plumegrass (Saccharum baldwinii), woolgrass (Scirpus cyperinus), and pale mannagrass (Torreyochloa pallida var. pallida).
Coastal Plain depression wetlands are relatively rare, small-patch communities that provide important habitat for the state-rare chicken turtle (Deirochelys reticularia) and three state-listed amphibians: Mabee's salamander (Ambystoma mabeei), tiger salamander (Ambystoma tigrinum), and barking tree frog (Hyla gratiosa). In addition, the globally rare plants Harper's fimbristylis (Fimbristylis perpusilla) and pondspice (Litsea_aestivalis) are confined to these habitats in Virginia.References: Fleming and Moorhead (1998), Rawinski (1997).
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Coastal Plain Seasonal Pond, dominated by plumegrasses (Saccharum baldwinii and S. giganteum), in flatwoods at Fort Lee Military Reservation, Prince George County. Photo: Nancy Van Alstine.
Two-ha (five-acre), isolated wetland dominated by willow oak (Quercus phellos), red maple (Acer rubrum), fetterbush (Eubotrys racemosa), and cypress-swamp sedge (Carex joorii). Near Beaumont, Powhatan County. Photo: Gary P. Fleming
Square-stem spikerush (Eleocharis quadrangulata) dominating a flooded Coastal Plain pond near Disputanta, Prince George County. Photo: Irvine Wilson.
Seasonally flooded woodland of swamp tupelo (Nyssa biflora) and cypress-swamp sedge (Carex joorii) in a wetland of the Grafton Ponds Natural Area Preserve in York County. Photo: Tom Rawinski.