Wetlands Types and Classifications
Wetlands have different characteristics. The most common feature of all wetlands is that the water table (the groundwater level) is very near to the soil surface or shallow water covers the surface for at least part of the year. The main characteristics of a wetland are determined by the combination of the salinity of the water in the wetland, the soil type and the plants and animals living in the wetland. Because of the high variability of the conditions, and because of the different needs for distinguishing among different types of wetlands, so far, there is no single wetlands classification system that would account for the manifold aspects of this specific ecosystem type. We will give more details about the two major types of classification of wetlands, discussed above the first is based on the traditional concept of a wetland, and the second is based on scientific grounds:
Figure 2 Marsh (source FORESTED WETLANDS: Functions, Benefits and the Use of Best Management Practices).
Figure 3 Tidal marsh along the Edisto River, South Carolina (source the US Environmental Protection Agency website).
Figure 4 Common Cattail (Typha latifolia) is a freshwater and estuarine marsh species (source US Environmental Protection Agency website).
Figure 5 Swamp (source FORESTED WETLANDS: Functions, Benefits and the Use of Best Management Practices).
The dominant vegetation, therefore, distinguishes the two major types of mineral soil wetlands: grasses dominate marshes, while trees dominate swamps. Both marshes and swamps may be freshwater or saltwater.
Generally these wetlands are referred to as "peatlands" in recognition of their common ability to form peat (organic soil produced by the accumulation of plant material). There are two major types of peatlands bogs and fens, both of which occur in similar climatic and geographic regions.
Figure 6 Bog (source FORESTED WETLANDS: Functions, Benefits and the Use of Best Management Practices).
Figure 7 Bog (source FORESTED WETLANDS: Functions, Benefits and the Use of Best Management Practices).
Figure 8 Fen (source the US Environmental Protection Agency website).
The two major types of organic soil wetlands are, therefore, distinguished by their hydrological regime (see Fig. 9): bogs receive water mainly from precipitation, while fens are supplied with water mostly from surface and groundwater sources:
Figure 9 Main differences between a bog and a fen (source FORESTED WETLANDS: Functions, Benefits and the Use of Best Management Practices).
Bogs and fens often occur side by side (FORESTED WETLANDS: Functions, Benefits and the Use of Best Management Practices). Often there is no strict borderline between the two wetland types but a smooth transition from one type to the other, as is the case of the Augstumal mire/peatland complex in Lithuania (see Figure 10):
Figure 10 Augstumal mire/peatland complex in Lithuania (source the International Mire Conservation Group website).
Unfortunately, the "traditional terminology" has the significant disadvantage of being based on the traditional concept of a wetland (see part on what wetlands are). As such, it takes into account comparatively few wetlands, mostly of inland freshwater character and of a relatively narrow climatic zone. Another great disadvantage of these traditional names is that many of them are highly localized for example, Johnson outlines that a "heath" in New Hampshire or Maine might be referred to as a "spong" in New Jersey (Johnson, 1985, in Johannesen and Gurganus), and Aber (2003) notes that the term "mire" is used mainly in Europe to denote any peatforming wetland (either bog or fen). To avoid these disadvantages, attempts have been made to develop a classification system that would take into consideration the various wetland types all over the world.
Figure 11 Classification hierarchy of wetlands and deepwater habitats, showing Systems, Subsystems and Classes. The Palustrine system does not include deepwater habitats (source Cowardin et al, 1979).
As initially developed, the classification system set up by Cowardin and co-workers (1979) did not include many wetland types that have resulted from human activities.
Ramsar Classification System for Wetland Type
(source the Convention on Wetlands website)
A Permanent shallow marine waters in most cases less than six metres deep at low tide; includes sea bays and straits.
B Marine subtidal aquatic beds; includes kelp beds, sea-grass beds, tropical marine meadows.
C Coral reefs.
D Rocky marine shores; includes rocky offshore islands, sea cliffs.
E Sand, shingle or pebble shores; includes sand bars, spits and sandy islets; includes dune systems and humid dune slacks.
F Estuarine waters; permanent water of estuaries and estuarine systems of deltas.
G Intertidal mud, sand or salt flats.
H Intertidal marshes; includes salt marshes, salt meadows, saltings, raised salt marshes; includes tidal brackish and freshwater marshes.
I Intertidal forested wetlands; includes mangrove swamps, nipah swamps and tidal freshwater swamp forests.
J Coastal brackish/saline lagoons; brackish to saline lagoons with at least one relatively narrow connection to the sea.
K Coastal freshwater lagoons; includes freshwater delta lagoons.
Zk(a) Karst and other subterranean hydrological systems, marine/coastal
L Permanent inland deltas.
M Permanent rivers/streams/creeks; includes waterfalls.
N Seasonal/intermittent/irregular rivers/streams/creeks.
O Permanent freshwater lakes (over 8 ha); includes large oxbow lakes.
P Seasonal/intermittent freshwater lakes (over 8 ha); includes floodplain lakes.
Q Permanent saline/brackish/alkaline lakes.
R Seasonal/intermittent saline/brackish/alkaline lakes and flats.
Sp Permanent saline/brackish/alkaline marshes/pools.
Ss Seasonal/intermittent saline/brackish/alkaline marshes/pools.
Tp Permanent freshwater marshes/pools; ponds (below 8 ha), marshes and swamps on inorganic soils; with emergent vegetation water-logged for at least most of the growing season.
Ts Seasonal/intermittent freshwater marshes/pools on inorganic soils; includes sloughs, potholes, seasonally flooded meadows, sedge marshes.
U Non-forested peatlands; includes shrub or open bogs, swamps, fens.
Va Alpine wetlands; includes alpine meadows, temporary waters from snowmelt.
Vt Tundra wetlands; includes tundra pools, temporary waters from snowmelt.
W Shrub-dominated wetlands; shrub swamps, shrub-dominated freshwater marshes, shrub carr, alder thicket on inorganic soils.
Xf Freshwater, tree-dominated wetlands; includes freshwater swamp forests, seasonally flooded forests, wooded swamps on inorganic soils.
Xp Forested peatlands; peatswamp forests.
Y Freshwater springs; oases.
Zg Geothermal wetlands
Zk(b) Karst and other subterranean hydrological systems, inland
Note : "floodplain" is a broad term used to refer to one or more wetland types, which may include examples from the R, Ss, Ts, W, Xf, Xp, or other wetland types. Some examples of floodplain wetlands are seasonally inundated grassland (including natural wet meadows), shrublands, woodlands and forests. Floodplain wetlands are not listed as a specific wetland type herein.
1 Aquaculture (e.g., fish/shrimp) ponds
2 Ponds; includes farm ponds, stock ponds, small tanks; (generally below 8 ha).
3 Irrigated land; includes irrigation channels and rice fields:
4 Seasonally flooded agricultural land (including intensively managed or grazed wet meadow or pasture).
5 Salt exploitation sites; salt pans, salines, etc.
6 Water storage areas; reservoirs/barrages/dams/impoundments (generally over 8 ha).
7 Excavations; gravel/brick/clay pits; borrow pits, mining pools.
8 Wastewater treatment areas; sewage farms, settling ponds, oxidation basins, etc.
9 Canals and drainage channels, ditches.
Zk(c) Karst and other subterranean hydrological systems, human-made