A wetland is a special area that is partly covered by water, either all the time or only during certain seasons. The water makes the soil very wet, which means there is less oxygen in the soil. Wetlands are found between areas of water and dry land. The plants that grow in wetlands have roots that can survive in wet, oxygen-poor soil. Wetlands are among the most diverse ecosystems on Earth, supporting many types of plants and animals. The plants in wetlands help improve water quality by removing extra nutrients like nitrates and phosphorus from the water.

Wetlands are found on every continent except Antarctica. The water in wetlands can be fresh, salty, or a mix of both. Wetlands are grouped into types based on the plants that grow there and where the water comes from. For example, marshes have plants like reeds and cattails that grow above the water. Swamps have trees and shrubs, though some swamps in Europe are covered with reeds instead of trees. Mangrove forests have trees and plants that can live in salty water.

Wetlands can be classified by the source of their water. Tidal wetlands get water from ocean tides. Estuaries have water from both tides and rivers. Floodplains receive water when rivers or lakes overflow. Bogs and vernal ponds get water from rain or melting snow, sometimes from underground springs. Some of the world’s largest wetlands include the Amazon River basin, the West Siberian Plain, the Pantanal in South America, and the Sundarbans in the Ganges-Brahmaputra delta.

Wetlands provide many benefits to people. They help clean water, protect shorelines from erosion, reduce the damage from storms, and control flooding. Wetlands also absorb and store carbon, which helps reduce the effects of climate change. However, they can also release gases like methane and nitrous oxide when organic material breaks down in wet, oxygen-poor conditions.

Human activities harm wetlands in many ways, such as drilling for oil and gas, building roads and buildings, overgrazing animals, overfishing, and polluting water. Wetlands are more at risk from environmental harm than any other ecosystem, according to a 2005 study. Scientists use methods to check the health of wetlands, which helps protect them. Since 1971, an international agreement has worked to identify and protect wetlands that are important for the whole world.

Definitions and terminology

A wetland is an area of land that is often covered with water. More specifically, wetlands are places where water covers the soil or is near the soil's surface for part or all of the year, including during the time when plants grow. A patch of land that becomes wet after rain may not be considered a wetland, even though it is temporarily wet. Wetlands have special features that set them apart from other land or water areas. These features include the level of water and the types of plants that live there. Wetlands are defined by having a water table (the level of water underground) that is close to the land's surface for long enough to support plants that grow in water.

A simpler definition is a community of soil that holds water and plants that grow in wet areas. Wetlands are also described as ecotones, which are areas that act as a bridge between dry land and water. They are different from both land and water but depend on both.

In decisions about the environment, specific definitions are used to help make rules and policies.

According to the Ramsar international wetland conservation treaty, wetlands are defined as:
– Areas with marshes, fens, peatlands, or water, whether natural or man-made, and whether the water is still or moving, fresh, brackish, or salty. This includes areas of the ocean where the water is no deeper than six meters at low tide.
– These areas may also include nearby land areas, such as riverbanks or coastal zones, and islands or ocean areas deeper than six meters that are part of the wetland.

An ecological definition of a wetland is an ecosystem where water covering the land creates soil conditions that support both oxygen-rich and oxygen-poor processes. These conditions cause plants and other living things to adapt to being flooded.

Sometimes, a legal definition of wetlands is needed. In the United States, wetlands are defined as areas that are often covered by water from the surface or underground. These areas support plants that grow in wet soil, such as those found in swamps, marshes, bogs, and similar places.

All definitions of wetlands focus on hydrology, which includes shallow water and soil that holds water. The soil, plants, and animals in wetlands are also often described in these definitions.

Wetlands can be tidal (flooded by ocean tides) or non-tidal. The water in wetlands can be fresh, brackish, salty, or alkaline. The four main types of wetlands are marshes, swamps, bogs, and fens (bogs and fens are types of peatlands). Some experts also recognize wet meadows and aquatic ecosystems as wetlands. Other types include mangrove forests, floodplains, and peatlands.

In Australia, wetlands are classified into three groups: marine and coastal wetlands, inland wetlands, and human-made wetlands. In the United States, the most well-known classification systems are the Cowardin system and the hydrogeomorphic (HGM) system. The Cowardin system includes five main types: marine (connected to the ocean), estuarine (between the ocean and rivers), riverine (within rivers), lacustrine (near lakes), and palustrine (inland, non-tidal areas).

Peatlands are a special type of wetland where plants grow quickly, and dead plants decay very slowly in waterlogged conditions. This process creates layers of organic peat. Bogs, fens, and mires are other names for peatlands.

Wetlands have different names in different regions. Examples include prairie potholes in North America, pocosins and Carolina bays in the southeastern United States, mallines in Argentina, Mediterranean seasonal ponds in Europe and California, turloughs in Ireland, and billabongs in Australia.

Wetlands are found worldwide in many climates. Temperatures vary depending on where the wetland is located. Many wetlands are in temperate zones, which are between the poles and the equator. These areas have warm summers and cold winters but not extreme temperatures. In subtropical zones, such as the Gulf of Mexico, average temperatures are about 11°C (52°F). Wetlands in tropical regions experience much higher temperatures for most of the year. In some areas, like the Arabian Peninsula, temperatures can exceed 50°C (122°F), leading to rapid water loss. In polar regions, such as northeastern Siberia, wetland temperatures can drop below −50°C (−58°F). Peatlands in Arctic and subarctic regions help protect frozen ground (permafrost) by slowing its melting and encouraging its formation.

The amount of rain a wetland receives depends on its location. Wetlands in Wales, Scotland, and western Ireland typically get about 1,500 mm of rain each year. In parts of Southeast Asia, where it rains heavily, wetlands can receive up to 10,000 mm of rain annually. In drier areas, wetlands may get as little as 180 mm of rain each year.

Wetlands can be classified into four types based on how often they are wet:
– Perennial systems: Always wet.
– Seasonal systems: Wet for part of the year.
– Episodic systems: Wet only occasionally.
– Ephemeral systems: Wet for a short time.

Some parts of wetlands may have water flowing on the surface, while other parts have water moving underground.

Processes

Wetlands differ because of local and regional changes in land shape, water movement, plant life, and other factors, such as human actions. Other important factors include soil fertility, natural events like fires or floods, competition between plants, plant-eating animals, soil burial, and salt levels. When dead plants form peat, bogs and fens form.

The most important reason wetlands exist is hydrology, or water movement. How long an area stays flooded or has wet soil determines if the wetland has water plants, marsh plants, or swamp plants. Other important factors include soil fertility, natural events, competition, plant-eating animals, burial, and salt levels. When peat from dead plants builds up, bogs and fens form.

Wetland water movement involves how water spreads across the land, how it flows, and its physical and chemical properties. Water enters wetlands mainly from rain, surface water (salt or fresh), and underground water. Water leaves wetlands through evaporation, water flowing over the surface, tides, and underground water movement. How water moves in and out of wetlands affects how water levels change over time.

Features of the land around wetlands influence water movement and water chemistry. Oxygen and carbon dioxide levels in water depend on temperature, air pressure, and mixing with air from wind or water flow. Water chemistry in wetlands is shaped by pH, salt, nutrients, conductivity, soil type, hardness, and water sources. Water chemistry changes depending on the landscape and climate. Most wetlands are minerotrophic (water contains minerals from soil), except ombrotrophic bogs, which get water only from rain.

Bogs mainly get water from rain and air moisture, so their water has low mineral content. Wetlands fed by underground water or tides have more dissolved nutrients and minerals.

Fen peatlands get water from both rain and underground water in different amounts, so their water chemistry ranges from acidic with low minerals to alkaline with high calcium and magnesium.

Salt levels strongly affect wetland water chemistry, especially in coastal areas and dry regions with little rain. Natural salt levels are controlled by how groundwater and surface water mix, which can be affected by human actions.

Carbon is the main nutrient cycled in wetlands. Many nutrients, such as sulfur, phosphorus, carbon, and nitrogen, are found in wetland soil. Oxygen-rich and oxygen-poor soil processes influence how carbon, hydrogen, oxygen, and nitrogen cycle, and how phosphorus dissolves, which affects water chemistry. Wetlands with very low pH and high salt levels may contain acid sulfates, while wetlands with average salt levels are often influenced by calcium or magnesium. Wetland chemical processes depend on soil with low redox potential.

Biology

Wetland ecosystems include plants (flora), animals (fauna), and microorganisms such as bacteria and fungi. The most important factor affecting wetlands is how long the area remains flooded. Other important factors include the fertility and salt content of the water or soil. The chemical composition of water entering wetlands depends on the water's source, the geological materials it flows through, and the nutrients released from organic matter in higher elevation soils and plants. Plants and animals in wetlands may change seasonally or based on flooding patterns.

There are four main groups of water plants found in wetlands worldwide. Submerged vegetation can grow in both salty and fresh water. Some species have underwater flowers, while others have long stems to help their flowers reach the water's surface. Submerged plants provide food for animals, habitat for invertebrates, and help clean water. Examples include seagrasses and eelgrass. Floating plants, such as duckweeds, are small and float on the water's surface. Emergent plants, like cattails, sedges, and arrow arum, grow above the water.

When trees and shrubs cover wetland areas with saturated soil, these regions are often called swamps. The boundary between swamps and drier land is influenced by water levels, which can be affected by dams. Some swamps are dominated by a single tree species, such as silver maple swamps near the Great Lakes. Others, like those in the Amazon basin, have many different tree species. Examples of swamps include cypress and mangrove swamps.

Many fish species rely on wetlands for survival. Seventy-five percent of the United States' commercial fish and shellfish depend entirely on estuaries to live. Amphibians, such as frogs and salamanders, need both land and water to reproduce and find food. Because amphibians often live in isolated wetlands like prairie potholes and Carolina bays, the connection between these wetlands helps control their populations. Tadpoles eat algae, while adult frogs eat insects. Frogs are sometimes used to show if an ecosystem is healthy because their thin skin absorbs nutrients and toxins from the environment, which can increase their risk of dying in polluted areas.

Reptiles such as snakes, lizards, turtles, alligators, and crocodiles live in wetlands in certain regions. In freshwater wetlands of the southeastern United States, alligators are common, and a type of freshwater crocodile lives in South Florida. The Florida Everglades is the only place where American crocodiles and alligators live together. Saltwater crocodiles live in estuaries and mangroves. Snapping turtles also live in wetlands.

Birds, especially waterfowl and waders, use wetlands often. Wetlands are home to many mammals, including small and medium-sized species like voles, bats, muskrats, and platypuses, as well as larger plant-eating and top predator species such as beavers, coypus, swamp rabbits, Florida panthers, jaguars, and moose. Wetlands attract mammals because they provide plenty of food, such as seeds, berries, and vegetation for herbivores, and many invertebrates, small reptiles, and amphibians for predators.

Invertebrates in wetlands include aquatic insects like dragonflies, bugs, beetles, midges, and mosquitoes, as well as crustaceans such as crabs, crayfish, shrimp, and tiny crustaceans, and mollusks like clams, mussels, snails, and worms. Invertebrates make up more than half of all known animal species in wetlands and are an important link in the food chain between plants and higher animals like fish and birds.

Ecosystem services

Wetlands perform different functions based on where they are located. These functions help provide many benefits to the environment and people. The United Nations Millennium Ecosystem Assessment and the Ramsar Convention describe wetlands as being very important for the environment and society in the following ways:

• Storing water to control flooding
• Helping to refill underground water sources
• Stabilizing shorelines and protecting against storms
• Cleaning water
• Treating wastewater in man-made wetlands
• Home to many different plants and animals
• Helping pollinate plants
• Providing materials from wetlands
• Cultural importance
• Offering opportunities for recreation and tourism
• Helping reduce the effects of climate change

According to the Ramsar Convention, replacing these wetland services would require spending large amounts of money on things like water treatment plants, dams, and levees. Many of these services cannot be replaced at all.

Floodplains and wetlands in closed depressions can act as storage areas and protect against floods. Floodplains are formed near the ends of rivers. "Floodplains of major rivers act like natural storage areas, allowing extra water to spread out over a wide area. This reduces the water’s depth and speed. Wetlands near the start of rivers and streams can slow down rainwater and snowmelt, preventing sudden floods downstream."

Examples of rivers with large floodplains include the Nile River, the Niger River inland delta, the Zambezi River floodplain, the Okavango River inland delta, the Kafue River floodplain, the Lake Bangweulu floodplain (Africa), Mississippi River (US), Amazon River (South America), Yangtze River (China), Danube River (Central Europe), and Murray-Darling River (Australia).

Groundwater can be refilled through wetlands such as marshes, swamps, and underground karst and cave systems. The visible water in wetlands is only part of the water cycle, which also includes water from the air (rain) and underground water. Many wetlands are directly connected to groundwater and help control the amount and quality of water below the ground. Wetlands with porous soil, like limestone, or in areas with changing water levels are especially important for refilling groundwater.

Soil and rock that allow water to pass through help water flow into underground water sources, which supply much of the world’s drinking water. Wetlands can also help refill groundwater when water levels are low and release water when levels are high.

Mangroves, coral reefs, and salt marshes help protect shorelines and reduce storm damage. Tidal and intertidal wetlands protect coastal areas. Coral reefs act as a barrier for shorelines. Mangroves stabilize the coast from the inside and move with the shoreline. These systems help reduce the speed and height of waves and floodwaters during storms.

The United Kingdom has started using a method called managed coastal realignment. This method protects shorelines by restoring natural wetlands instead of using engineering. In East Asia, coastal wetlands have been greatly reduced due to development, with up to 65% of wetlands lost. One study estimated that wetlands provide a natural storm protection service worth about US$33,000 per hectare each year.

Wetlands help clean water by trapping sediments and nutrients. They act as a buffer between land and water. Plants in wetlands absorb, store, and remove nutrients like nitrate from runoff water.

Rain and runoff can cause soil erosion, moving sediment into waterways. Wetland plants slow water flow and trap sediment for short or long periods. Sediment can contain harmful metals that are also trapped when wetlands stop sediment from moving.

Wetlands are very good at removing nutrients and trapping sediment, but they have limits. Too much pollution from fertilizers, sewage, or erosion can cause problems like too many nutrients in water. Deforestation can also harm wetlands by causing too much sediment to enter them, leading to loss of plants and animals.

Constructed wetlands are man-made wetlands used to treat wastewater. An example is the East Kolkata Wetlands in India, which cover 125 square kilometers and help treat the city’s sewage. Nutrients from the wastewater support fish farming and agriculture.

Constructed wetlands are artificial systems designed to treat sewage, greywater, stormwater, or industrial waste. They can also help reclaim land after mining or protect natural areas lost to development. These systems use natural processes like plants, soil, and organisms to clean water. The design depends on the type of wastewater being treated. Constructed wetlands are used in both large and small wastewater systems. Primary treatment is needed if there is a lot of solid waste or organic matter.

Like natural wetlands, constructed wetlands help remove pollutants such as organic matter, nutrients, and harmful substances from water. They can also reduce the number of disease-causing germs in water. Wetlands below the surface are better at removing germs than those on the surface.

Wetlands are important for biodiversity, as highlighted by the Ramsar Convention and World Wildlife Fund. Protecting wetlands helps create jobs, support communities, and ensure sustainability. An example is the Lower Mekong basin, which supports over 55 million people in Cambodia, Laos, and Vietnam.

A fish species called the Piramutaba catfish, Brachyplatystoma vaillantii, travels more than 3,300 kilometers from the mouth of the Amazon River to its spawning grounds in Andean rivers. Along the way, it helps spread plant seeds.

Intertidal mudflats have high productivity even though they have few species. The many small animals in the mud provide food for migrating birds.

Mudflats, salt marshes, mangroves, and seagrass beds have high levels of both the number of species and the amount of resources they produce.

Disturbances and human impacts

Wetlands, along with the services they provide and the plants and animals that live there, can be harmed by different types of disturbances. These disturbances, which may also be called stressors or changes, can be caused by humans or natural events, and they can be direct or indirect, temporary or long-lasting, and isolated or combined with other effects.

Examples of disturbances include natural events like flooding or drought. Humans also harm wetlands by activities such as extracting oil and gas, building roads and buildings, overgrazing animals, catching too many fish, changing wetlands by dredging or draining them, and polluting water with nutrients or chemicals. The impact of a disturbance depends on its type and how long it lasts.

Common disturbances of wetlands include:

Disturbances can be grouped into three categories:

• Minor disturbance: Causes little harm and helps the ecosystem stay healthy.
• Moderate disturbance: Damages the ecosystem, but it can recover on its own over time.
• Severe disturbance: Requires human help for the ecosystem to recover.

Nutrient pollution happens when too much nitrogen enters water systems. This increases the amount of nitrogen in wetlands, leading to eutrophication, which harms the balance of life in these areas.

Biodiversity loss in wetlands occurs due to changes in land use, destruction of habitats, pollution, overuse of resources, and the spread of non-native species. For example, plants like water hyacinth, which originally grew in South America, and duckweed, which was introduced to parts of Australia, have taken over wetlands in new areas. These plants crowd out native species, reducing the variety of plants and animals that live there.

To grow crops, wetlands are sometimes turned into dry land using barriers and drainage systems. Building these structures harms wetlands and the larger areas they are connected to. Wetlands are often near rivers and lakes, so they are developed for human homes. Once homes are built and protected by barriers, the land becomes more likely to sink and flood. The Mississippi River Delta near New Orleans, Louisiana, and the Danube Delta in Europe are examples of this.

Water pollution is another major cause of wetlands being lost. Wetlands hold water longer than other water bodies, so they can collect harmful chemicals from pollution. These chemicals harm native plants and animals, reducing biodiversity. Wetlands in high mountain areas show this loss of life clearly.

Draining floodplains or building structures that narrow floodplain areas, like levees, reduces the ability of rivers and their floodplains to control flooding. These changes force rivers to handle the same amount of water in smaller areas, leading to stronger and faster floods.

In the past century, human-made structures like dykes, bunds, levees, weirs, barrages, and dams have damaged floodplain wetlands. These structures direct water into a main river channel, limiting the natural spread of water over wide, shallow areas. This loss of wetlands increases the risk of severe flooding. For example, during Hurricane Katrina, a levee failure in New Orleans caused hundreds of deaths. Along the Yangtze River, human-made barriers have increased the frequency and severity of flooding, leading to loss of riverbank plants, soil erosion, and reduced water storage in floodplain lakes.

Overfishing is a serious problem for wetlands. Farm fishing, which uses wetlands and waterways to raise fish for people to eat, is growing rapidly, especially in China, where 90% of aquaculture farms are located. This industry contributes 80% of the world’s aquaculture value. However, practices like shrimp farming have destroyed large areas of wetlands, such as mangroves. Although the harm caused by shrimp farming is well known, it is difficult to stop because people in these areas often lack other job opportunities. At the same time, global demand for shrimp continues to grow, making it hard to reduce this impact.

Conservation

Wetlands have been drained for development, such as building homes, farms, or creating lakes for recreation and hydropower. Many of the world's most important farming areas were once wetlands that were turned into farmland. Since the 1970s, more attention has been given to protecting wetlands to keep their natural roles. Between 1900 and now, more than half of the world's wetlands have been lost. To keep wetlands healthy and working well, changes that go beyond what is normal should be avoided.

Wetlands are important ecosystems that help people who live near them have better lives. Research shows that it is possible to protect wetlands while also improving the lives of people nearby. Studies in Malawi and Zambia looked at how dambos—wet, grassy valleys or low areas where water rises from underground—can be farmed in a way that is not harmful to the environment. Results included high crop production, new farming methods, and water management plans that provide enough water for farming.

The Ramsar Convention (full name: Convention on Wetlands of International Importance, especially as Waterfowl Habitat) is an international agreement aimed at solving problems related to wetland loss and damage. The main goals of the treaty are to identify wetlands that are important worldwide and to encourage their use in a way that protects them. Methods include limiting access to certain wetland areas and teaching people that wetlands are not wastelands but valuable ecosystems. The convention works with five international partners: BirdLife International, IUCN, the International Water Management Institute, Wetlands International, and the World Wide Fund for Nature. These partners help with research, education, and funding to support wetland protection.

Restoration

Restoration ecologists work to help wetlands return to their natural state by supporting the natural processes of the ecosystem. These methods differ based on how much the environment is physically changed and are linked to different levels of restoration. Restoration is needed after a wetland is disturbed or damaged. There is no single way to restore a wetland, and the level of restoration required depends on the amount of damage. However, every method of restoration requires planning and careful management.

Factors that influence the chosen approach include budget, time limits, project goals, the level of damage, landscape and ecological conditions, political and administrative decisions, and social and economic priorities.

In one strategy, no physical changes are made to the environment. Instead, the ecosystem is left to recover naturally through a process called succession. The focus is to stop further damage and ensure the wetland can recover on its own. This method requires research to determine if the wetland can naturally recover. It is often the first choice because it is the least disruptive and least costly, though some small, non-intrusive changes, like controlled burns or planting specific plants, may help speed up recovery. Examples include burning small areas, encouraging soil microbes and plant growth through planting, and increasing the variety of habitats to support more species. These actions help remove obstacles and allow natural species to thrive.

Another strategy combines natural recovery with more active management. This may involve engineering work, such as breaking up soil, using herbicides or insecticides, spreading mulch, planting seeds mechanically, or planting trees on a large scale. In these cases, the wetland is too damaged to recover without human help. Restoration methods must be chosen based on the specific needs of each location, considering the level of damage and local ecosystem conditions. Some partial restoration methods include using semi-natural wetlands, like paddy fields, which are farmland flooded during planting seasons. These areas require human care but can help reduce flooding in inland regions.

The most expensive and disruptive method involves completely rebuilding the ecosystem from the ground up. Since the entire system is redesigned, it is important to consider the wetland’s natural path and choose plant species that will help the ecosystem return to its original state.

In many cases, constructed wetlands are built to treat stormwater or wastewater. They are used in urban areas as part of systems that manage water more effectively. These wetlands help reduce flooding, remove pollutants, store carbon, provide habitats for wildlife, and support biodiversity in cities where natural areas are limited.

Wetlands help reduce flooding in several ways. They can hold extra water during heavy rains or high water flow, which lowers the area, depth, and length of floods. They also slow down water movement, reducing damage to ecosystems and nearby property.

Traditional ecological knowledge can guide wetland restoration by considering how all parts of the ecosystem are connected. These practices include monitoring wetland resources, planting seeds or young plants, and adding key species to create a self-sustaining wetland. These methods improve productivity, biodiversity, and the wetland’s ability to withstand challenges.

Climate change aspects

In Southeast Asia, peat swamp forests and their soils are being dried up, burned, mined, and overgrazed, which contributes to climate change. When peat is drained, the carbon that built up over thousands of years—usually kept underwater—is exposed to the air. This causes the peat to break down and release carbon dioxide (CO₂) into the atmosphere. Peat fires speed up this process and also create large clouds of smoke that travel across international borders, which happens nearly every year in Southeast Asia. Although peatlands cover only 3% of Earth’s land, their destruction produces 7% of all CO₂ emissions globally.

Wetlands are a major source of greenhouse gases, mainly methane and nitrous oxide. Wetlands are the largest natural source of methane in the world, making them a key concern for climate change. They release about 20–30% of all methane in the atmosphere, adding roughly 161 million tonnes of methane each year.

Wetlands are defined by wet, waterlogged soils and unique plant and animal life that live in water-rich environments. These conditions support methane production because wetlands lack oxygen. Microbes in warm, moist areas use oxygen faster than it can be replaced from the air, creating ideal conditions for methane-producing bacteria. However, methane production depends on factors like oxygen levels, soil temperature, and soil composition. Warmer, wetter soils with more organic material allow for more methane production.

Some wetlands release methane and also emit nitrous oxide, a greenhouse gas 300 times more powerful than CO₂. Nitrous oxide is the main substance that harms the ozone layer today. Wetlands can also absorb greenhouse gases.

Studies show that coastal wetlands, also called blue carbon ecosystems, can help reduce climate change in two ways: by protecting them to stop carbon emissions from their loss, and by restoring them to increase CO₂ absorption and long-term storage. However, using coastal wetlands for CO₂ removal may not be cost-effective if only climate change solutions are considered.

When wetlands are restored, they help reduce climate change by storing carbon. Through photosynthesis, plants convert CO₂ into solid material, and wetlands also help regulate water. Globally, wetlands store about 44.6 million tonnes of carbon each year. Salt marshes and mangrove swamps, in particular, absorb about 210 grams of CO₂ per square meter yearly, while peatlands absorb 20–30 grams of CO₂ per square meter yearly.

Coastal wetlands, like tropical mangroves and temperate salt marshes, store carbon that would otherwise contribute to climate change as CO₂ or methane. These wetlands help reduce methane emissions from tidal areas, leading to efforts to protect and improve their carbon-storing abilities.

Restoring coastal wetlands benefits climate change adaptation, coastal protection, food production, and biodiversity.

Since the middle of the 20th century, human-caused climate change has changed the global water cycle. A warmer climate increases the severity of extreme wet and dry events, leading to more floods and droughts. Wetlands help with climate change adaptation by providing services like storing water, controlling floods, replenishing groundwater, stabilizing shorelines, and protecting against storms. In most parts of the world, changes in the water cycle and extreme weather are expected to increase faster than average climate changes.

Valuation

To understand the value of wetlands to local communities, scientists first map the wetlands in a region. Then, they study the wetlands to learn about the benefits they provide, such as cleaning water, supporting wildlife, and preventing floods. After collecting this information, they use it to decide which wetlands need the most protection, restoration, or management. Over time, scientists keep records of all known wetlands and monitor a group of wetlands to track changes caused by natural events or human activities.

Scientists use quick methods to evaluate wetlands. These methods help them score, rank, or categorize wetland benefits, the health of the wetland, and the presence of plants or animals. This is often done to decide which wetlands should be protected or to find ways to replace wetland benefits lost due to development, such as by restoring wetlands in other areas. These methods are also used before and after wetlands are restored or changed to see how those actions affect the wetlands. Assessments are considered "quick" if they take less than a day to complete, which may include looking at satellite images or using computer tools like GIS, but not detailed lab tests of water or soil samples.

To make sure different scientists get similar results, quick methods use standardized forms with questions or checklists. These forms help combine answers into estimates of how well a wetland functions compared to other wetlands studied before. These methods use many indicators, such as conditions inside and around the wetland, to give more accurate and repeatable results than just naming the wetland type. Quick assessments are needed when government agencies have deadlines for decisions or when many wetlands need evaluation.

Creating a complete list of all wetlands worldwide is very challenging. However, many local efforts have been successful. Current methods rely on available data, but sometimes the details of wetlands are not clear enough for planning. Small, long, or narrow wetlands are hard to identify. Some satellite images lack the detail needed to monitor wetlands, but newer satellite data, like from IKONOS and QuickBird, may help if the resolution is 4 meters or better. Many images mix different plants, making it hard to see wetland vegetation. However, 3D data from LiDAR technology has helped improve mapping in some areas.

Wetlands must be monitored over time to see if they are healthy or if they are becoming damaged. Damaged wetlands may have worse water quality, fewer special plants or animals, and problems with soil processes.

Many wetlands are hard to monitor from the ground because they are in hard-to-reach areas or have dangerous plants, animals, or diseases. Tools like satellite images and aerial photos help scientists map and monitor wetlands over large areas. Combining data from different sources, like LiDAR and aerial photos, with modern computer methods, such as deep learning, makes mapping more accurate. Using digital data helps create consistent records and allows information to be shared in a geographic information system.

Legislation

The Ramsar Convention on Wetlands of International Importance Especially as Waterfowl Habitat is an agreement between countries to protect and use wetlands wisely. It is also called the Convention on Wetlands. The name comes from the city of Ramsar in Iran, where the agreement was signed in 1971.

Every three years, leaders from countries that signed the agreement meet in a group called the Conference of the Contracting Parties (COP). This group makes decisions about how to protect wetlands, such as choosing new wetland areas to protect and setting rules for wetland care. In 2022, COP15 took place in Montreal, Canada.

Each country has its own way of defining wetlands for legal reasons. In the United States, wetlands are described as areas that are often covered by water or soaked by groundwater long enough to support plants that grow in wet soil. These areas usually include swamps, marshes, bogs, and similar places. This definition is used to enforce the Clean Water Act. Some states, like Massachusetts and New York, have their own definitions that may differ from the national one.

In the United States Code, a wetland is defined as land that (A) has soil that holds water, (B) is covered by water or soaked by groundwater often enough to support plants that grow in wet soil, and (C) normally supports these plants. The term "normal circumstances" means conditions that happen during the wet part of the growing season under typical weather, not during unusually dry or wet times. It is common for wetlands to be dry for long parts of the growing season. However, under typical conditions, the soil will be covered by water, creating conditions without oxygen that last through the wet part of the growing season.

• Wetlands and wetland policies in Canada
• Other Individual Provincial and Territorial Based Policies

Examples

Some of the largest wetlands in the world are the swamp forests in the Amazon River region, the peatlands in the West Siberian Plain, the Pantanal in South America, and the Sundarbans in the Ganges-Brahmaputra delta.