WETLAND: CHARACTERISTICS, RELIEF, FLORA, CLIMATE, FAUNA, EXAMPLES - GEOGRAPHY - 2025

The wetland is an ecosystem formed by flooded or saturated lands, or bodies of water close to land that includes aquatic and terrestrial environments. The flood regime can be temporary or permanent and the source of water can be surface, underground or precipitation.

In a wetland, water can saturate the rhizosphere or cover the soil surface up to 10 m above. The rhizosphere is the zone with the highest proportion of roots in the soil that occupies the first 30-50 cm.

Pantanal in Brazil. Source: Leandro de Almeida Luciano

Wetlands are protected at the international level by the Ramsar Convention that entered into force in 1975. Under this convention, extensions of marshes, swamps and peatlands are included as wetlands. Likewise, wetlands are considered to be surfaces covered by water, whether natural or artificial, permanent or temporary, stagnant or flowing.

Therefore, it includes fresh, brackish or salty waters such as extensions of sea water whose depth at low tide does not exceed six meters. Hydrological and biogeochemical processes and associated flora and fauna are fundamental in these ecosystems.

Many of the plant species that inhabit wetlands have developed special adaptations to survive in these environments. Environmental conditions are characterized by a low oxygen concentration in the roots and in some cases high salinity.

Wetlands are azonal because their distribution is not influenced by latitude and longitude, as well as having no predetermined climate or soils.

The two most widely used classifications of wetlands are the United States National Inventory of Wetlands and the Ramsar Convention. There are seven main types of wetlands which are marine-coastal, estuarine, river-riparian, lake, marsh, geothermal and artificial.

Estuaries, marshes, coral reefs, mangroves, rivers, floodplains, lakes, swamps, peatlands, geysers, and constructions such as lagoons, canals, and ponds are covered.

Wetlands occur on all continents and at all latitudes and heights above sea level. The relief is varied from concave, low plains or plateaus and includes rivers and protected areas of low coasts.

The flora and fauna is very diverse, given the variability and geographic scope of the wetlands. You can find terrestrial, amphibian and aquatic animals and tropical, temperate and cold environments. The vegetation can be not very diverse and sparse as in the peat bogs of Tierra del Fuego or Siberia, or very diverse and exuberant as in the Amazon jungle.

The wetlands are the scene of various economic activities, including fishing, fish farming, breeding, hunting as well as the extraction of different resources. Some resources exploited in these ecosystems are wood, fibers and resins from forests as well as peat in peatlands.

The Ramsar convention has registered 2,370 wetlands, although there are many more that exist in the world. Some of these are under protection figures like national parks.

As an example of wetlands at a global level, we can point to the overflow or flood forests in the Amazon River basin. Equally noteworthy are the bogs of the Kurukinka Park in the Chilean Tierra del Fuego or the marshes of the Doñana National and Natural Park (Spain).

Another wetland is the largest wetland area in Europe in the Sjaunja Nature Reserve (Sweden). In turn, the largest wetland on the planet is the Pantanal, located in the Mato Grosso and Mato Grosso do Sul region of Brazil, reaching as far as Paraguay and Bolivia. It has an incredible area of ​​340,500 km².

General characteristics

- The definition of wetland

There is no universally accepted definition of wetlands, since they are complex ecosystems that oscillate between terrestrial and aquatic.

The Ramsar Convention applies a broad definition that includes wetlands as deep-sea habitats such as rivers, lakes and bays. While the US Fish and Wildlife Service differentiates wetlands and deep-sea habitats.

Another definition is that of the Committee for the Characterization of Wetlands of the United States. In this, in addition to the condition of saturation or flooding, the presence of hydric soils and hydrophilic plants is emphasized.

- Functional characteristics

Among the factors that determine the functioning of the wetland are its geomorphology, hydrology, biogeochemical processes, vegetation and fauna.

Geomorphology and hydrology

Geomorphology refers to the conformation of the terrain, which varies in each particular wetland. The conformation of the terrain affects the hydrology, which in turn determines the dynamics of the water in the wetland (hydrodynamics).

Water sources and hydrodynamics

The wetland can receive water from rivers, the sea or both, or it can come mainly from rainfall. Another source of origin for wetland water comes from underground sources.

Sediments

The contributions of rivers and the sea have a particular relevance given the dynamics that they generate around the dragging and deposition of sediments. These include mineral and organic nutrients useful to food chains.

Likewise, these deposits and trawls affect the morphology of the terrain and therefore the hydrodynamics of the wetland.

Biogeochemical processes

As the wetland is a transitional ecosystem between the terrestrial and aquatic environment, it determines certain particular processes. The water saturation of the substrate generates anaerobic processes.

In some cases, such as peatlands, acidic waters are combined with aerobic-anaerobic processes that are responsible for the formation of peat.

Processes such as denitrification (conversion of nitrates into nitrogen), occur in wetlands with high concentrations of organic matter and anoxia. Anoxia (lack of oxygen) occurs depending on the degree of water saturation of the soil.

Another factor that intervenes is the contributions of nitrates, which vary from wetland to wetland. For example, in boreal peatlands they come from precipitation and in alluvial plains of rivers by runoff from agricultural areas.

Likewise, sulfate reduction and methanogenesis processes occur due to bacterial action. Sulfide production occurs in salt marshes while methane production is common under ombrotrophic conditions.

The ombrotrophic conditions occur in peatlands and refers to the fact that the nutrients and water are provided by precipitation.

Hydroperiod

The variables that most define the wetland are the depth, duration, frequency and seasonality of the flood. In the case of arid climates, the interannual variation of the hydroperiod is particularly important.

- Floors

Soils can be highly variable in texture and structure, depending on the type of wetland in question. However, the most characteristic condition as a general type of reference is hydromorphic or hydric soil.

These are soils affected in their properties by the condition of being subjected to flooding.

The biology of the wetland

Vegetation and fauna are an active part of the dynamics of the wetland since the density and type of vegetation affect the loss of water by evapotranspiration. In some cases certain animal species are true managers of the wetland, for example beavers (Castor sp.).

These rodents have the ability to build dams that are their refuge sites and that alter the water regime of the area.

The rhizosphere and the wetland

A terrestrial ecosystem differs from a wetland because in the former the rhizosphere is free of water saturation. The rhizosphere is the layer of soil where the greatest number of roots develop, generally in the first 30-50 cm from the ground.

In wetlands, the water level rises above the soil surface or at least reaches up to the rhizosphere. This forces the plants to develop certain adaptations to survive in this condition.

On the other hand, some wetlands reach considerable flooding above the substrate level. They include aquatic animals, such as fish, crocodiles, manatees, among others.

Adaptations

Plant adaptations to survive flood conditions are varied and depend on the type of wetland. For example, mangroves develop complex morphoanatomic systems that facilitate aeration of the roots.

They also have glands in their leaves that allow them to expel the salt they absorb with seawater.

Marsh grasses in swamps, marshes, and other wetlands develop aeriferous tissue in their roots, facilitating the movement of oxygen. Floating aquatic plants also have this tissue in their leaves that allows them to float.

In wetlands, wading birds are common, with long legs so they can walk through flooded areas. At the same time they have sharp beaks for harpooning fish.

- The Ramsar Convention

It was one of the first international conventions on the environment and was signed in Ramsar (Iran) in 1971 (in force since 1975). Its objective is the conservation and wise use of the planet's wetlands, given their importance as sources of drinking water.

For 2019 there are 170 signatory countries, covering 2,370 wetlands with a total area of ​​252,562,111 hectares.

- Types of wetlands

Proposals for classifying wetlands include the United States National Inventory of Wetlands and the Ramsar Convention. However, to simplify the complex diversity of wetlands we can focus on 7 wetland systems:

Marine-coastal wetlands

They are coastal wetlands and include coastal lagoons, coastlines, rocky shores, and coral reefs. Towards the sea they contemplate the open marine waters of little depth and inland as far as the splashing of the waves influences.

Estuarine wetlands

They are semi-enclosed seascapes, encompassing deltas, tidal-flooded marshes, fjords, estuaries, and mangroves. In general, any partially closed coastal area where fresh and marine water mix, reaching different degrees of dilution.

These wetlands are more influenced by the terrestrial environment than in the case of marine-coastal wetlands.

In some cases, the salinity of the substrate may be higher than that of the open sea as in closed estuaries and some mangroves. This is because evaporation increases the concentration of salts.

On the other hand, it may happen that the dilution of the saline concentration penetrates outside waters such as in the deltas of large rivers.

River and riparian wetlands

They form along rivers and other watercourses as well as floodplains within them. These are deep-water wetlands contained in a canal.

These wetlands can be classified into subsystems depending on the water regime of the river as perennial or intermittent flow, including its variations.

In the riparian wetlands, the flood lagoons stand out, which are flat or concave areas formed by the sediments carried by the river. These sediments are periodically deposited on the plain with the river's peak flow peaks causing flooding.

This deposition of sediments originates different riparian ecosystems such as swamps, lagoons, overflow forests, among others.

Riparian wetlands occupy variable spaces determined by the size and characteristics of the basin. For example, the jungles of the Amazon River floodplain are up to 100 km wide.

In the Amazon we find two types of forest: flood or overflow, which are the várzea and the igapó.

The Várzea jungle is formed by the overflowing of white water rivers (waters rich in mineral sediments). The igapó is a forest flooded by rivers of black waters (rich in organic matter).

Lake wetlands

They are those associated with lakes and can have different origins, being volcanic, glacial, fluvial, marine, tectonic and even due to meteorite impact.

They also vary according to the depth and salinity of their waters as well as their source. Among these are permanent lakes fed by rivers and precipitation.

There are ephemeral saline lakes in arid zones maintained mainly by underground water discharges.

The lagoons can be originated by depressions in the ground of depth superior to the phreatic level. These fresh or salt water lagoons are formed in areas where rainfall exceeds evapotranspiration.

Marshy wetlands

The water source is mainly underground or due to precipitation and comes from contributions from rivers in internal deltas. Among the marshy wetlands there are some with a layer of free water and others where the water level is subsurface.

Also, in this group are flooded grasslands, oases, swamps and peat bogs, which are the most abundant type of wetland.

Peatlands are ecosystems that are located in areas where there is an excess of humidity. Although they occur mainly in temperate and cold zones, tropical peatlands are also found.

The formation of the peat bog requires greater precipitation than evapotranspiration and high relative humidity throughout the year. In addition, acidic waters are associated for the partial decomposition of organic matter to occur.

Under these conditions, the organic matter rots and undergoes partial carbonification (loss of hydrogens), forming the so-called peat. This is due to the action of aerobic bacteria on partially water-covered organic matter.

Geothermal wetlands

It includes all sources of hot springs, such as geysers, hot springs, sulfur springs, fumaroles and others. These waters are heated by geothermal energy generated by magma intrusions.

There are about 400-900 geysers in the world, of which 200-500 are in the Great Yellowstone Geyser Basin (USA).

Artificial wetlands

They are all those built by humans, such as fish and shrimp ponds and farm ponds and lagoons. Likewise, agricultural lands irrigated by floods such as rice fields, artificial salt pans, treatment plants and canals.

- Location in the world

There are wetlands in almost every country in the world, at various latitudes, from the tundra to the tropics. It is estimated that 6% of the planet's land surface is covered by wetlands.

Most are peatlands (50%) and swamps, followed by floodplains, coral reefs, mangroves, and finally lakes and lagoons.

Peat bogs

The deepest and most extensive peat deposits are found in the northern and southern temperate and cold bogs (90%). In the northern hemisphere they are in Alaska, northern Canada, Iceland, northern Europe and Asia

Peatbog. Source: isol

The largest peatlands are those found in the Siberian tundra and although they are associated with cold climates, there are also peatlands in the tropics.

Most are in shallow deposits in the Brazilian Amazon and deep in Peru, Ecuador and Argentina. This represents 44% in area and volume of all tropical peatlands.

In Asia, especially in Indonesia, there are 38% of tropical peatlands. There are also extensive deposits in the Congo Basin in Africa.

Floodplain or floodplain

In South America there are large floodplains associated with the larger basins (Amazonas, Orinoco and Paraná). In Africa there are those of the Nile River and the Congo River and in Asia there is the alluvial plain of the Yellow River.

Mangroves

About 60-75% of the coastline of the tropical regions of the world is covered with mangroves. This encompasses America (Atlantic and Pacific coast), Africa (Atlantic and Indian coast), India, all of Southeast Asia, and tropical Oceania.

Deltas

All the great rivers that flow into the sea form a diversion cone due to the deposition of sediments, forming multiple arms. There are deltas on every continent, forming extensive alluvial plains.

The delta of the Nile River and the Congo in Africa and Asia, the Ganges delta in India-Bangladesh and the Yellow River in China stand out. For South America the delta of the Amazon and the Orinoco stand out.

On the other hand, we can mention the Colorado and Mississippi delta in North America and in Europe the Ebro delta and the Camargue delta (Rhone River).

Swamps

Swamps are found on all continents and climates and thus in Europe the largest wetland area is Sjaunja in Sweden, with 285,000 hectares. In North America extensive swamps are located in the Everglades at the southern tip of the Florida peninsula.

Wetland in Everglades National Park (United States). Source: National Park Service

In South America we find large swampy areas such as the Pantanal in southwestern Brazil, reaching Paraguay and Bolivia. As well as the Bañados de Otuquis in the southeast of Bolivia, near the border with Paraguay and Brazil.

Relief

Wetlands develop in flat places, such as coastal plains, low coasts, inland plains, or on plateaus. They can be located from altitudes below sea level to high plateaus close to 4,000 meters above sea level.

Thus, the floodplains of northern South America are plains established in depressions below sea level. For its part, the Lhalu wetland, in the Tibet Autonomous Region (southwest China), is located at 3,645 meters above sea level.

In general, wetlands develop in six basic types of terrain:

- Depressions in the ground that favor the accumulation of water.

- Tidal strips defined by the ebb and flow of the tide in coastal areas.

- Lake strips, determined by changes in the level of lakes.

- Fluvial, conditioned by the diversions of rivers, their variations in level and overflows.

- In areas of irregular and permeable terrain, they form springs, underground rivers and other deposits.

- Plains, which can generate different types of wetlands depending on their origin and characteristics.

Flora

Given the geographic and structural diversity of wetlands worldwide, their flora is quite variable. In general, it is made up of species adapted to the conditions of substrates saturated with water and deficit of radical oxygen.

- Peat bogs

Peatland vegetation in cool and temperate zones is treeless and made up of low grass and mosses. For example, mosses such as Acrocladium auriculatum and Sphagnum magellanicum predominate in Chilean peatlands.

Likewise, there are cushion herbs such as donatia (Donatia fascicularis) and astelia (Astelia pumila).

- Amazonian overflow forests: várzeas and igapós

The Amazon jungle is one of the places with the greatest diversity of life on the planet, with up to 285 species per hectare. However, the diversity is lower in the flooded forests, especially in the igapós (due to the acidity of the water due to organic acids).

Some species of trees typical of the flooded or overflow forest are Cecropia latiloba, Macrolobium acaciifolium and Nectandra amazonum.

- Mangroves

The species of plants that inhabit the mangrove are adapted to withstand the high concentrations of salts in seawater. Among them are the red mangrove (Rhizophora mangle), the black mangrove (Avicennia germinans) and the white mangrove (Laguncularia racemosa).

- Marshes

In these environments, the species must adapt to the high salinity of the substrate (halophytes). In the American marshes there are species such as the saladillo (Sporobolus virginicus) and various species of Atriplex (called salt plants).

Species such as marshmallow (Althaea officinalis) and salted chard (Limonium vulgare) are found in Europe. Some such as seagrass (Zostera marina) can even form submerged meadows together with algae.

- Aquatic plants

A fundamental element in the vegetation of wetlands are aquatic plants, which can be emergent or submerged. They can also be rooted to the bottom or float in the liquid medium.

In the mangroves there are submerged grasslands of Thalassia testudinum and in the South American lagoons and flooded plains the bora or water lily (Eichhornia spp.).

Victoria amazonica. Source: Wolves201

The Victoria amazonica lives in the Amazon with floating leaves 1-2 m in diameter and stems up to 8 meters rooted at the bottom.

Weather

Wetlands cover a great diversity of sites, from sea level to mountains and at all latitudes. Therefore it does not have a specific climate and can exist in cold, temperate and tropical climates.

Arctic, cold and dry climates such as the peat bogs of the Siberian tundra or warm rainy climates such as the Amazonian floodplain can occur. Likewise, arid climates of deserts such as oases in the Sahara or in humid climates in deltas such as some mangroves.

Fauna

Given the high diversity of habitats where wetlands develop, the fauna associated with them is also very rich.

- Rivers and streams

In the fluvial currents the species of fish and crustaceans abound and some aquatic mammals like the river dolphin (platanistoids). In the rivers and streams of the forests of some regions of the northern hemisphere, the beaver (Castor canadensis and C. fiber) stands out.

This animal stands out due to the fact that its habits imply an administration of the water regime of the wetland. The beaver knocks down trees with its teeth and builds dams to create ponds where they live and creates wetlands by regulating the flow of rivers.

- Amazonian overflow forests: várzeas and igapós

Among other species is the jaguar (Panthera onca) that hunts in these areas both in the dry season and in flood periods. Others such as the manatee (Trichechus manatus) invade the jungle properties when the water penetrates it.

- Mangrove

In the mangroves there are species typical of the terrestrial part (mammals, birds, insects), and other aquatic species such as fish and turtles. For example, the green turtle (Chelonia mydas) uses Thalassia testudinum grasslands as a food source.

In Southeast Asia, the Asian elephant (Elephas maximus) descends into the mangrove to feed. The mangroves of this region also inhabit the marine crocodile (Crocodylus porosus).

- Marshes and coastal lagoons

Seabirds abound, particularly waders characterized by having long legs that allow them to wade through shallow waters. A very characteristic example is the flamingo (Phoenicopterus spp.) Which is a large bird.

The flamingo enters shallow places and feeds by filtering the water from the marshes with its beak to capture small crustaceans and algae.

- Floodplains or plain alluvial plains

Both aquatic and terrestrial species abound in the overflow plains of the llaneros rivers and some that share both habitats. For example, in the floodplains of northern South America we find the spectacled caiman (Caiman crocodilus) and the anaconda (Eunectes murinus).

Likewise, the jaguar and capybara (Hydrochoerus hydrochaeris) inhabit these areas; as well as various species of herons.

The capybara is an animal adapted to the wetland, resting and feeding both in water and on land. On land it consumes grasses from the pasture and in the water it feeds on aquatic herbs.

- Peat bogs

The boreal bogs are part of the habitat of the reindeer (Rangifer tarandus) as a foraging area. These animals migrate in summer to the tundra where large areas of peatlands are found.

There they mainly feed on the abundant mosses that adapt very well to the acidic and oxygen-deficient radical environment.

- swamps

A species of crocodile (Crocodylus acutus) and an alligator (Alligator mississippiensis) live in the Everglades swamps. In addition, it is inhabited by the Caribbean manatee (Trichechus manatus) and the Canadian otter (Lontra canadensis).

American alligator (Alligator mississippiensis). Source: gailhampshire from Cradley, Malvern, UK

In these swamps you can find numerous species of birds such as the American flamingo (Phoenicopterus ruber).

Economic activities

- Agriculture, livestock, fishing and fish farming

Fishing

The most relevant economic activity is fishing, with estuaries and deltas being very productive fishing areas.

Pisciculture

Fish farming takes place both in natural wetlands or in artificial wetlands (ponds built by man).

Crops

A characteristic crop of wetland areas is rice (Oryza sativa), whose traditional form of production is in flooded melgas. In this crop, irrigation by continuous flooding is applied, thus constituting an artificial wetland.

Cattle raising

The flood plains are well adapted to the calf of the Water Buffalo (Bubalus bubalis) and the Capybara. In the latter case it is more about natural population management than a breeding system itself.

Breeding

In tropical America there are confined breeding systems for the spectacled caiman by skin and meat consumption.

- hunting

Crocodile hunting is practiced in the wetlands of the Gulf of Mexico, Florida and Louisiana (USA). This is done illegally in some cases, while in others it is regulated.

- Tourism

Because of their importance, wetlands are protected worldwide, in the form of national parks and nature reserves. In these areas one of the priority activities is tourism for the natural beauties associated with the wetland.

- Resource extraction

Given the diversity of wetlands, the resources that are extracted are equally diverse. Wood, fruits, fibers and resins, among others, are obtained from the jungles and the peat that is used as fuel is extracted from the bogs.

Peat can also be used as organic compost and to improve moisture retention in agricultural soils.

For the indigenous people of the Amazon, the várzea jungle areas are among the most productive for obtaining their food.

Examples of wetlands in the world

Marshland

It is the largest wetland on the planet, with an area of ​​340,500 km2 located in the Mato Grosso and Mato Grosso do Sul region of Brazil. The pantanal continues to extend and reaches Paraguay and Bolivia.

It consists of a depression formed when the Andes Mountains rise, to which a series of rivers discharge. The main of these rivers is the Paraguay, which feeds this depression on its way to the Paraná River.

Additionally, there are contributions from precipitation, since the region has a rainfall of 1,000 to 1,400 mm per year.

Amazon floodplain forests: várzea and igapós

The great rivers of the Amazon basin present periodic overflows, flooding about 4% of the Amazonian territory. The sheet of water reaches a depth of up to 10 m and penetrates into the jungle up to 20 km, so it is estimated that it is flooded.

These areas present dense tropical forests with up to 5-6 layers of vegetation. The water covers up to a quarter of the length of the tallest trees and totally the understory and smaller trees.

The soils are not very fertile, but those of the várzea forests are among the most fertile in this basin. This higher fertility is associated with the contributions of sediments from flood waters.

Under these conditions, an ecosystem is generated where aquatic animals feed on the fruits that fall from the trees. The fish known as the Amazonian arawana (Osteoglossum bicirrhosum) hunts insects and even bats and small birds that are in the branches.

Kurukinka Park: peat bogs of Chile

It is located on the Big Island of Tierra del Fuego in Chile, and biogeographically corresponds to the Antarctic kingdom. It is a private park managed by an international conservation organization called the Wildlife Conservation Society based in New York.

It is home to forests of lenga or southern beech (Nothofagus pumilio) and mixed forests of this species with coigüe or oak (Nothofagus dombeyi). Likewise, there are extensive peat bogs dominated by mosses and herbaceous species of angiosperms.

Among the fauna, the guanaco (Lama guanicoe) and the culpeo fox (Lycalopex culpaeus) and the black-necked swan (Cygnus melancoryphus) stand out. Unfortunately, the beaver was introduced in this area and has generated important changes in the habitat.

Doñana National and Natural Park (Spain)

It is located in the southwest of the Iberian Peninsula, in the autonomous community of Andalusia. This park protects an area that is part of the marshes of the Guadalquivir river.

Marsh in Doñana National Park (Spain). Source: Dvazquezq

It is an old coastal cove filled with marine and river deposits that extends over 122,487 hectares. The area is an important reserve for aquatic birds, especially migratory birds, due to its Mediterranean location and proximity to Africa.

In the park there are about 300 species of birds, such as the stone curlew (Burhinus oedicnemus) and the cinnamon jar (Tadorna ferruginea). The Iberian lynx (Lynx lynx), the wild boar (Sus scrofa) and the European hedgehog (Erinaceus europaeus) also live here.

Among the plants there are grasses such as Vulpia fontquerana and gymnosperms such as Juniperus macrocarpa (maritime juniper).

Sjaunja Nature Reserve (Sweden)

Sjaunja is the second largest nature reserve in Sweden, established in 1986 being the largest wetland area in Europe with some 285,000 hectares. It includes mountainous areas, marshes and swamps as well as broadleaf and coniferous forests.

It is found in the region of the Sami people (reindeer herders) and inhabits species of ducks, geese, wading birds, swans and raptors.

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