Ecology of the Mississippi River Delta Region

The following wetlands classification is adapted from Cowardin et al. (1979).

PALUSTRINE WETLANDS
All non-tidal freshwater wetlands containing trees, shrubs, emergents; also, such habitats where tidal driven salinity is below 0.5 ppt. Non-tidal wetlands lacking these plant characteristics and being less than 20 acres in size are also palustrine. Includes the following types of Palustrine Wetlands:

• Bottomland hardwoods - Basically, the alluvial plains of rivers, characterized by a mixture of trees and other vegetation that can tolerate occasional flooding (gum, oak, ash, maples, hackberry, holly, bays, magnolia, elderberry, etc.)
• Swamps- Areas that are usually flooded and have woody vegetation. In the south, the characteristic species include Bald Cypress (Taxodium disticum) and Tupelo gum (Nyssa aquatica) (hence "cypress-tupelo swamps"). Their natural salinity is very near 0 ppt.
• Marsh - Areas with standing water for part of the year that also contain non-woody standing vegetation.
• Freshwater marsh - Marshes having a salinity range of 0-2 ppt with very high plant species diversity (at least 89 species of plants representing >0.01% of the total). Typical resident plants include Cattail (Typha), Water Lilies (Nymphaea, Nymphoides, and Nuphar), Sedge (Scirpus), and many, many more.
• Floatant marsh - A type of marsh, usually found in freshwater or intermediate situations, composed of thick, floating mats of vegetation with open water beneath.
• Intermediate marsh - Marshes having a salinity range of 2+-10 ppt with high plant species diversity (about 51 species of plants representing >0.01% of the total). Visually, these marshes exhibit a mix of freshwater and brackish marshes, having Wiregrass (Spartina patens) and such plants as Cattail (Typha), Water Lilies (Nymphaea, Nymphoides, and Nuphar), Sedge (Scirpus), etc.
• Brackish marsh - Marshes having a salinity of 10+-20 ppt with moderate plant species diversity (about 36 species of plants representing >0.01% of the total). The characteristic plant is Wiregrass (Spartina patens) (usually more than 50% of the total vegetation).[see Estuarine Wetlands section below for the final type of marsh - saline, or salt]
• Fens - Alkaline wetlands fed by ground water and drainage rather than precipitation. Accumulate peat.
• Bogs - Peat-accumulating wetlands that receive most of their water from precipitation and exist where a high water table waterlogs the soil. Precipitation leaches out the nutrients and the bogs are acidic. Have acid adapted plants, especially sphagnum moss.
• Mire - European name for peat-accumulating wetland that is soggy and muddy.
• Moor - European name for an open high area, also peat-accumulating, and usually wet.
• Peatland - Generic term for any area that accumulates peat.
• Muskeg - Large zones of peatlands, usually interspersed with coniferous trees, in boreal areas such as Canada and Alaska.
• Pocosins - A swamp in an upland coastal zone. This term is used in the southeastern U.S., especially in the coastal portions of the Carolinas.
• Wet prairie - Basically, prairie whose plant assemblages are tolerant of periodic submergence.
• Prairie potholes - Shallow marshes in midwestern U.S. prairie region. Formed by glaciation. May contain other types of wetlands such as fens, saline ponds, and the like. Usually do not have inlets or outlets. Other glacial lakes include kettle lakes, cirque lakes, and thaw lakes.
• Playa lakes - Shallow marshes in southwestern U.S. desert basins.
• Wet (or Sedge) Meadows - Places where water saturates the soil for most of the year but usually doesn't stand at the surface of the soil.
• Slough - May be Palustrine, Lacustrine, or Riverine, depending on usage. In the southeastern U.S., usually a slow moving swamp or marsh; in the north and midwest, a swamp or shallow lake; in the west, a channel into a coastal marsh from the ocean or estuary.

RIVERINE WETLANDS
Basically, rivers, streams, bayous, etc. with sparse vegetation. All freshwater wetlands contained within a channel. Subject to the nature of the channel (bottom type, slope, source of water, etc.). Includes rivers, creeks, bayous, canals, and the like. Salinity is less than 0.5 ppt. When plants are present, they are often rooted in the bottom (water lilies, algae) and are most abundant in eddys along the margins.

ESTUARINE WETLANDS
Tidally influenced bodies of water and their adjacent wetlands that are semienclosed by land but are at least periodically open to the sea at one end and have freshwater flowing into the other. Subject to salinity fluctuations depending on the amount of freshwater received from adjacent river(s) and the amount of sea water from the adjacent sea.
Specific zones:

• Open estuary -The open water portion. Salinity may range from fresh near the mouths of rivers and bayous to very saline near the open sea.
• Saline (salt) marsh -Marshes having a salinity of >20 ppt (frequently full sea water: 35 ppt) with low plant species diversity (about 13 species of plants representing >0.01% of the total). The characteristic plant is Oyster grass (Spartina alterniflora) (usually more than 60%, not infrequently 100%, of the total vegetation). Black Rush (Juncus romerianus) may also be abundant, as is Pickleweed (Salicornia sp.) and Batis (Batis maritima). [Though part of the Palustrine Wetlands, the other types of marsh feed the Estuarine Wetlands and may be found nearby.]

MARINE WETLANDS
The open sea over the continental shelf. Subject to waves, currents, and tides. Salinity is typically 30+ ppt (sea water is 35 ppt). Vegetation includes algae and phytoplankton.

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