Outforia Quicktake: Key Takeaways
- Wetlands are highly productive ecosystems that are home to diverse plant and animal species
- There are 4 main types of wetlands: marshes, swamps, bogs, and fens
- Wetlands can be classified depending on factors such as vegetation cover, water source, and land shape
- Wetlands provide vital services, including flood reduction, habitat for wildlife, water filtration, and erosion control
- Human activity and climate change have led to the decline of many wetlands around the world
Wetlands are recognized as some of the most productive ecosystems in the entire world. Wetland is an umbrella term that includes several different types of wetlands. Each wetland has its own unique characteristics.
Marshes, swamps, bogs, and fens are the four main types of wetlands. However, these wetlands can be broken down even further depending on their specific features.
What is a Wetland?
Wetlands are areas of land that have saturated soils or shallow water covering the surface for most of the year. The saturation of the soil and land is most dominant in wetlands.
Although water can build up in depressions after excessive rainfall, these instances can be temporary. Wetland soils or substrates maintain a heightened level of saturation for extended periods of time.
Some wetlands have substrate that’s completely covered with water for most of the year. Wetlands may dry up during the summer or in droughts, but this is usually the only time when water is less dominant.
Wetlands are special ecosystems because there are many plants and animals that can’t live in deeply saturated lands. Wetland animals and plants have unique adaptations that allow them to survive in the habitat.
Classification of Wetlands
Wetlands are classified in different ways. Wetland classification systems consider different characteristics of wetlands to determine the type. Some factors that are considered to classify wetlands include vegetation cover, water source, and land shape and position.
Lewis M. Cowardin created the Cowardin wetland classification system in the 1970s for the US Fish and Wildlife Service (FWS). The system recognizes five major types of wetlands, including:
- Marine – Marine wetlands are associated with open ocean waters that cover coastlines almost all the time or part of the time. This system is separated into two subclasses, which include subtidal and intertidal.
- Estuarine – These wetlands are more associated with land than the open ocean like marine systems. Estuarine wetlands are often a mix of freshwater and saltwater that comes farther inland.
- Lacustrine – Lacustrine wetlands are associated with land depressions. They’re also described as having more than 30% of emergent moss or lichen coverage.
These wetlands consist only of freshwater and are usually fed by permanent bodies of water, such as lakes.
- Palustrine – Palustrine systems are nontidal wetlands that may include or lack vegetation and aren’t associated with permanent bodies of water like lacustrine systems.
- Riverine – Riverine wetlands are associated with channels of moving water, such as rivers or streams.
Another wetland classification system is used by the US Army Corps of Engineers. These wetland classifications may sound more familiar. The US Army Corps of Engineers describe four main types of wetlands:
Each of these wetlands, except for fens, include subclasses that have different characteristics. When we jump into all the different types of wetlands, we’ll be using the US Army Corps of Engineers classification system.
Types of Wetlands
Each section will describe the major type of wetland, followed by its subclasses. Marshes have the most subclasses compared to other types of wetlands, with at least 8 different variations. Fens are the only type of wetlands that don’t have any specific subclasses.
Marshes have saturated soils with some vegetation. The main water source for water is surface water from precipitation. Some of the water collected in marshes also comes from groundwater.
Marshes associated with tides usually have a higher salt content than inland marshes. The pH level of marshes is typically neutral.
1.1 Inland Marshes
Inland marshes occur more on land. They’re not associated with open ocean tides or coasts. Inland marshes are categorized into different subclasses, all of which consist of freshwater.
These marshes can be super helpful to areas vulnerable to drought. They help replenish groundwater supplies and provide an extra water source to flowing water.
Everglades are subtropical freshwater marshes. One of the most notable everglades marshes is found in southern Florida. Known as the Florida Everglades, the extensive wetlands cover about two million acres of the state.
There are two main types of soils that occur in the Florida Everglades, which include marl and peat. Marl is dead algae and peat is waterlogged dead plant matter.
Much of the Florida Everglades are found in the Everglades National Park. The area is very biodiverse, housing a wide variety of species.
More than 360 bird species use the Everglades as habitat and feeding grounds. The Everglades also act as a rest stop for migratory birds passing through the area.
The ecosystem is home to endangered native species, such the Florida panther and West Indian manatee.
1.1.2 Prairie Potholes
Prairie potholes are freshwater marshes that develop in land depressions. The main water source for this type of wetland is precipitation.
Prairie potholes are found in regions with glaciated landscapes that have lots of depressions, or potholes.
Prairie potholes are most common in the northern Midwest. They may fill with water in the winter due to snowmelt or excessive rainfall in the spring and summer. Sometimes prairie potholes may dry up. Others stay saturated year-round.
These wetlands have many beneficial purposes. They collect rainfall and snowmelt, which reduces the risk of flooding. They also provide feeding and breeding grounds for migratory waterfowl and many other animals.
1.1.3 Wet Meadows
Wet meadows are freshwater inland marshes that form in low-lying fields or lake basins. They’re described as wet meadows because they’re mainly associated with grasslands. Wet meadows aren’t as saturated as other types of wetlands, unless after rainfall.
Groundwater is the main water source because the water table is higher in these low-lying areas. Wet meadows are rarely covered with surface water and may dry up at certain times of the year.
A variety of grasses that thrive in saturated soils can be found in this wetland, such as sedges and rushes.
1.1.4 Vernal Pools
Vernal pools are classified as seasonal wetlands because they’re covered with shallow water in the wet season and dry up in the dry season. These wetlands are most common in regions subject to warm, wet winters and dry, hot summers.
Vernal pools can be found in the west coast of the US and some areas in the Northeast and Midwest.
Depressions in the land collect water during the wet season, usually in the winter and spring months. They often dry up in the late spring and summer.
California once had an abundance of these wetlands, but has since lost more than 90% of its vernal pools.
1.1.5 Playa Lakes
Playa lakes are inland marshes exclusive to the Southern High Plains region in the US. Rounded deep depressions in the land collect fresh rainwater during the spring. This is the only time of the year when playa lakes remain dominated by water.
The origins of playa lakes is unclear, but they may have formed as a result of subsidence.
The freshwater collected in playa lakes supports a wide variety of wildlife, such as whooping cranes, bald eagles, and amphibians.
1.2 Freshwater Tidal Marshes
In the US, freshwater tidal marshes are mainly found in the mid-Atlantic coastal plain region. The Chesapeake Bay houses extensive freshwater tidal marsh wetlands.
The water levels in these marshes are affected by tides. The freshwater comes from flowing water sources, runoff, and groundwater.
1.3 Tidal Saltwater Marshes
Saltwater tidal marshes occur in coastal areas. They’re primarily sourced by ocean tides. The saline content in these marshes are higher than freshwater tidal marshes.
Also called salt marshes, these wetlands consist of spongy decomposing plant matter and saturated soil.
A salt marsh will usually maintain its surface water year-round. This causes the oxygen levels to be extremely low. Only unique plant species that can survive water dominated wetlands are capable of living in such low oxygen levels.
Some of the benefits of these wetlands include food sources, erosion protection, and flood prevention. Many fishes that provide food sources for coastal communities live in these marshes, such as blue crab and shrimp.
Swamps are heavily vegetated wetlands that collect water from precipitation. Swamps usually consist of freshwater. Saltwater swamps exist as a result of saltwater floodplains that feed the wetland with saltwater.
One of the most important swamps in the mid-Atlantic region is the Great Dismal Swamp located in southeastern Virginia and northeastern North Carolina.
The Great Dismal Swamp National Wildlife Refuge provides protection to the 113,000 acre area. The swamp used to cover about one million acres between the two states.
Another great swamp on the east coast is found in the Georgia Okefenokee National Wildlife Refuge. The refuge consists of 353,981 acres of protected land.
Rare and endangered species are protected in this area, such as the wood stork and red-cockaded woodpecker. The swamp houses more than 600 different types of plants.
Swamps have two main subclasses categorized by the type of vegetation present in them.
2.1 Forested Swamps
Swamps that contain an abundance of trees are classified as forested swamps. These swamps can be found all throughout the US.
Most forested swamps are fed by flowing water sources. They’re critical to reducing the risk of flooding.
Forested swamps usually maintain a certain level of surface water. Sometimes the ground is covered in several feet of slow moving or stagnant water. Even if annual precipitation levels are low, a forested swamp can still have shallow surface water.
Forested swamps found in the southeast and south central US are often called bottomland hardwood swamps. These swamps are usually found along riversides in broad floodplains.
Almost 30 million acres of bottomland hardwood swamps once occurred throughout the southern US about 200 years ago.
A significant portion of these wetlands has been lost since then, primarily due to draining for agricultural use.
Other examples of forested swamps include cypress swamps, which mainly consist of bald cypress trees. Other trees that occur in forested swamps include red maples, willows, western hemlock, and pin oak. Types of trees can vary depending on the region.
2.2 Shrub Swamps
Swamps dominated by shrubs are referred to as shrub swamps. Shrub swamps have similar characteristics as forested swamps, but they’re dominated by shrubs instead of trees.
These swamps are also fed by flowing water systems. They’re usually submerged in water for most of the year.
Mangrove swamps may be classified as forested or shrub swamps. A mangrove swamp is dominated by shrubs and trees belonging to the mangrove family.
Mangroves are specially adapted to swamp ecosystems and can handle heavily saturated soils with relatively high salt content. Many mangrove swamps occur throughout southern Florida.
Bogs differ from other wetlands because of the type of plant matter found in them. The water is also acidic and has very low nutrient levels.
There are two main types of bogs, which are categorized by where they’re located and how they develop.
3.1 Northern Bogs
Northern bogs are mainly found in the northern US where glacial lakes once occurred. Large amounts of moisture are drawn in by northern bogs due to rainfall or snow melt and high levels of humidity.
The high acid content of bogs allows only certain types of plants to grow, such as peat and carnivorous plants.
Heavy layers of peat moss may cover northern bogs. The heavy coverage protects the water from evaporating. This process is called paludification.
3.2 Pocosin Bogs
Bogs found in the southeastern US are referred to as pocosin bogs. Pocosin is a term derived from the Algonquin Native American language, which translates to “swamp on a hill”.
The largest concentration of pocosin bogs is found in North Carolina. Rainfall is the primary water source for these wetlands.
While many northern bogs may have surface water for most of the year, pocosin bogs typically have no standing water. However, they’re classified as wetlands because the soil is heavily saturated almost all year.
Pocosin bogs may become dry during the spring or summer, causing natural fires. Peat moss, sand, and charcoal are the primary components of the soil in pocosin bogs.
Fens are similar to bogs because they contain peat mosses. The biggest difference between the two is fens don’t receive most of their water from precipitation.
Most of the water in fens comes from groundwater and drainage. Due to the differences in water sources, fens have more nutrients and lower acidity levels.
If peat moss builds up in a fen and fills it in a process called terrestrialization, it can turn into a bog.
Most fens in the US can be found in northeastern states, the Rocky Mountains, and the Great Lakes region. They can also be found throughout Canada. Along with peat moss, fens have other forms of vegetation like grasses, wildflowers, and sedges.
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Where Are Wetlands Located?
Wetlands can be found all around the world, except Antarctica. The wide ranging characteristics allow them to form in many places.
Since some wetlands develop primarily from precipitation, ample groundwater or other water sources may not be necessary to form. However, wetlands that rely mainly on rivers and streams are typically located near flowing water systems.
Tidal wetlands occur in coastal areas and some inland areas with estuaries.
South America is home to the largest tropical wetland in the world, the Pantanal.
About 5.5% of US land is wetlands, most of which are freshwater.
The type of wetlands you could find depend on where you live. The southeastern US has an abundance of mangrove swamps and a vast everglades marsh.
Mid-Atlantic and northeastern states have several types of wetlands. Playa lakes and vernal pools can be found in parts of the western US.
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Why Are Wetlands Important?
Wetlands are productive ecosystems that provide habitat to a wide range of plant and animal species. Since wetlands support such a great variety of fauna and flora, they promote biodiversity.
Each type of wetland serves special purposes for the areas where they’re located. Some of the benefits that wetlands provide include:
- Flood reduction or prevention
- Habitat and breeding and feeding grounds for wildlife
- Act as natural water quality filters
- Erosion control and prevention
- Farming for various human food sources
Wetlands provide a place where flood water can escape. Without wetlands, areas could suffer from flooding and harm humans, wildlife, and non-aquatic plants.
Many migratory birds and waterfowl depend on wetlands for feeding during long migrations. Reptiles, amphibians, microbial communities, and mammals also depend on wetlands for their needs.
Wetlands have the ability to act as a natural water filter, which can improve the quality of water in an area.
These ecosystems can collect runoff, which contains excess nutrients that pollute water sources. Wetlands can also protect water sources from other forms of pollution.
Coastal wetlands are especially helpful in preventing erosion by binding substrate.
Although draining wetlands for agricultural use can be harmful, wetlands provide food sources for humans. Cranberry and wild rice farms may be located in wetlands. Fisheries use coastal wetlands to collect shrimp, crabs, and oysters.
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Conservation Status of Wetlands in the US
A vast amount of wetlands have been lost in the US over the past few centuries. The biggest threat to wetlands is human activity, but some threats occur naturally.
California has lost more than 90% of its wetlands since 1780. Other states that have lost more than 80% of their wetlands since the late 18th century include Ohio and Iowa.
More than 20 states have lost more than 50% of their original wetlands.
Based on data collected in the 1970s and ‘80s, there were approximately 96.5 million acres of wetlands throughout the lower 48 states. According to the US Environmental Protection Agency, it’s estimated that 220 million acres of wetlands once existed in the lower 48 states in the 1600s.
Between 1996 and 2016, human development contributed to about 640,000 acres of wetlands lost.
Alaska has more than 150 million acres of wetlands, which is significantly more than any other state.
A variety of human activities contribute to the loss of wetlands, such as:
- Drainage for agricultural use
- River or stream dredging
- Construction of dams
- Runoff and pollutants
- Logging and mining
Warming temperatures as a result of climate change have also affected wetlands. Extended drought periods prevent some wetlands from receiving enough water to maintain saturated soils.
The introduction of non-native plant and animal species harms the biodiversity of wetlands.
Many wetlands have been lost due to draining for urban development. Wetlands are also drained for farming because of the fertile soils they provide.
What are the 3 largest wetlands in the world?
The largest wetland in the world is a tropical wetland called the Pantanal. It’s located in South America, mainly in Brazil and part of Bolivia and Paraguay.
The Pantanal spans across 42 million acres of the continent. It’s home to more than 4,700 plants and animals, making it one of the most biodiverse ecosystems in the world.
The Ngiri-Tumba-Maindombe is a freshwater wetland found in the Democratic Republic of the Congo. It’s the largest body of freshwater on the entire continent of Africa.
The area is recognized as internationally important by the RAMSAR Convention on Wetlands. The total area is about 16.2 million acres (6.57 million hectares).
The Queen Maude Gulf Migratory Bird Sanctuary found in northern Canada is the world’s second largest RAMSAR wetland in the world. It covers about 15.5 million acres (6.27 million hectares) and provides habitat for many migratory birds.
What is the largest wetland in the USA?
The Atchafalaya River Basin is the largest wetland found in North America. It spans across almost one acre of land in Louisiana.
Most of the Atchafalaya River Basin is forested swamplands. A smaller portion of the basin is marsh. Bald cypresses are the dominant trees in the forested swamp area. The basin sources its water from the Atchafalaya River, which is fed by the Gulf of Mexico.
What is the most common wetland?
Non-tidal marshes are the most common type of wetlands found in the US, according to the EPA. They’re widely distributed across the country. Most non-tidal marshes in the US are freshwater. Some may be brackish or alkaline.
What is the most interesting wetland in the world?
The Pantanal is widely considered one of the most interesting wetlands in the world. It’s not only interesting for its size, but it has large concentrations of unique species like crocodiles and jaguars. It contains about 10 million caimans, which are food sources that attract jaguars.
Other dense populations of animals found in the wetland include tapirs and giant river otters. It’s home to more than 600 different bird species, such as the vulnerable hyacinth macaw.