How Wetlands Work

Alaska Image Gallery The Stikine River wetlands in southeast Alaska. See more pictures of Alaska.
Alaska Image Gallery The Stikine River wetlands in southeast Alaska. See more pictures of Alaska.
Carr Clifton/Minden Pictures/Getty Images

Water lilies, turtles, frogs, ducks, snakes, dragonflies, minnows, herons, sticky black muck, monsters, the body of Jimmy Hoffa. What do these things have in common? Wetlands.

A wetland is an area between dry land and water that is regularly saturated with surface or ground water. In fact, it's inundated with this water so consistently that vegetation and animals that thrive in wet conditions take up residence there. You can find wetlands on every continent on the planet, with the exception of Antarctica [source: EPA].


Since wetlands are so common and found almost everywhere, why is wetland preservation such a big deal? Actually, up until the mid-1980s, it wasn't. Wetlands were viewed as wild areas that needed to be controlled. The U.S. Army Corps of Engineers, in particular, spent a lot of time draining wetlands for future development or agriculture. In fact, since European settlers first arrived in what would become the United States, U.S. wetland area has declined from 220 million acres to 105.5 million acres [source: Zinn]. That's a 50 percent loss.

During the 1970s, people began to recognize the benefits of wetlands. In addition to hosting a wide variety of plant and animal life, wetlands also provide water storage, filtration and offer us protection from floods. Beginning with The Clean Water Act of 1972, the U.S. government began instituting a series of laws and acts that would protect wetlands from further degradation. Unfortunately, the majority of wetlands in this country are located on private land, so the government can only do so much. The government also has recently put focus on restoration and wetland creation.

Worldwide, threats to wetlands continue. Human exploitation, climate change, military activity, and drought all degrade or destroy the planet's wetland areas. For instance, in only 30 years, the Philippines has lost 80 percent of its coastal wetlands [source: WWF].

What­ lives in wetlands, and why do wetlands go by so many different names? Keep reading to find out.

Benefits of Wetlands

Lilly pads and colorful birds -- residents of the wetlands.
Lilly pads and colorful birds -- residents of the wetlands.
Richard Du Toit/Minden Pictures/Getty Images

At one time, people believed wetlands were useless, and they were drained for development. But we now realize that wetlands are a valuable and crucial part of the world's ecosystem. Let's talk about some of the many benefits wetlands provide.

When you're doing the dishes or washing your car, you probably use a sponge to soak up the water. Think of wetlands as a giant sponge, slowly absorbing water and releasing it when necessary. The sponge-like quality of wetlands allows them to return water to the ground during dry periods. Wetlands also slow down water's momentum as it travels to the ocean or the river, and less momentum means less soil erosion.


Because wetlands slow the flow of water down, they're also able to filtrate the water. Wi­thout that momentum, the water travels around plants and vegetation more slowly. As a result, any suspended sediment drops out of the flow. This natural cleansing helps to keep pollution, toxins and nutrients out of the water system. Water overloaded with nutrients is susceptible to algae bloom, which can be very destructive to plant and animal life [source: EPA].

Wetlands are comparable to rainforests in the amount of species they can support (it's no wonder they attract nature photographers and wildlife enthusiasts). The abundant vegetation and shallow water levels in wetlands play host to many plant and animal species. What types of animals thrive in a wetland depends on the type of wetland, but can include muskrats, beavers, moose, raccoons, bobcats, swamp rabbits, and white-tailed deer. Wetland birds include bald eagles, ospreys, hawks, egrets, herons and kingfishers [source: CTIC]. Some of the more familiar fish and shellfish that depend on wetlands for survival include flounder, sea trout, striped bass, shrimp, oysters, clams, and blue and Dungeness crabs. And many species of birds rely on wetlands for breeding or nesting grounds, including ducks, geese, woodpeckers, hawks and wading birds [source: EPA].

Wetlands aren't just lovely to look at. They also protect us against floods. Like your car's brakes, wetlands halt the velocity of floodwaters and help to disperse the excess water. Undisturbed wetlands can store up to 60 days of floodwater [source: EPA]. When coastal wetlands are lost, it leads to weakened storm buffers. Wetlands can also act as a buffer against colder temperatures. As farmland has replaced wetlands, crops have become more susceptible to frost -- even in south Florida [source: O'Connor].

What are the different types of wetlands and how do they form? Find out on the next page.


Types of Wetlands

Cypress trees are common to wetlands, like these in a Charleston, S.C. swamp.
Cypress trees are common to wetlands, like these in a Charleston, S.C. swamp.
Eric Keil/Aurora/Getty Images

Wetlands can form naturally or through animal or human activity. Common causes of natural wetlands include:

  • Floodwaters from nearby lakes or rivers
  • Saturation from rain and runoff
  • Groundwater close to the surface that continually flows up
  • Coastal waters that often immerse nearby land

In addition­, wetlands ­might form when beavers dam a river or stream. The diversion of w­ater causes flooding and, as a result, wetlands develop. U.S. state agencies also may intentionally flood dry areas to encourage wetland formation to host wetland-dependent species.


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There are actually several types of wetlands. The U.S. Environmental Protection Agency (EPA) categorizes wetlands into marshes, swamps, bogs and fens. Though they have differences, they all serve the environment by acting as a buffer against flooding, absorbing excess nutrients, and providing habitats for a wide variety of species. Let's take a closer look at ­each type­.

A marsh is a wetland frequently or continually filled with water. Marshes can be found on the coast and inland, and can be either freshwater or saltwater. Characterized by grassy, soft vegetation that grows in the soggy soil conditions, marshes can be one of two types -- tidal or non-tidal. Found along coastlines, tidal marshes are most prevalent on the eastern coast of the United States and in the Gulf of Mexico. Non-tidal marshes are the most common type of wetlands in North America and occur along the boundaries of streams, rivers, ponds and lakes. Water is generally only a few inches or feet deep with soil that's extremely mineral-rich and organic. Non-tidal marshes host vegetation like lily pads, cattails, and reeds as well as a varied sample of animal life, including muskrats, otters, blue herons and blackbirds.

A swamp is any wetland dominated by woody plants and several feet of water. The Everglades in Florida is one example of a swamp. As with most wetlands, swamps function as flood protection and nutrient removal. The saturated ground and standing water form a black,­ thick and nutritious soil, providing a favorable environment for water-tolerant shrubs and trees. Fittingly, then, there are two types of swamps -- shrub swamps and forested swamps­. The difference between the two swamps simply is the type of vegetation present. You will often find shr­ub swamps and forest swamps adjacent to each other. Shrub swamps are swamps filled with lower, bushy vegetation such as willow, dogwood, swamp rose and mangroves. Forested swamps host trees like red maple, pin oak, tupelo, cypress and willows. They play a vital role in the survival of wetland-dependent animals, like ducks, snakes and otters.

Bogs receive most of their water from precipitation, rather than runoff or floodwaters. Their spongy, mossy floors contain fewer nutrients than a marsh or swamp. As the moss decomposes, it forms acidic peat. Acidic peat will burn for a very long time, and people harvest it for fuel. This peat is also very low in nutrients, and only specially adapted creatures may call a bog home, like salamanders, dragonflies, snakes and carnivorous plants. Found mostly in the northeast U.S. and Great Lakes regions, bogs are also an excellent area to grow cranberries.

A fen is similar to a bog, except that a fen receives its water from the ground­ rather than from precipitation. The water that feeds a fen is actually water from melted glaciers. As the glacier melts, it deposits sand and gravel into the soil, preventing its runoff from permeating into the soil. Instead, it flows sideways and picks up minerals and sediment as it travels. This means a fen's ­water is much more rich and nutritious than a bog. Therefore, fens host a diverse community of plants and animals. Wildflowers, deer, turtles, butterflies and even fish may find a home in a fen. Fens are rare, found primarily in the northern hemisphere in areas with low temperatures. It can take up to 10,000 years for a fen to form naturally [sources: EPA and U.S. Fish & Wildlife Service].

In the next section, we'll examine the threats to wetlands. How quickly are wetlands disappearing?

Threats to Wetlands

A drought-stricken wetland in Sri Lanka, with elephant tracks through the mud.
A drought-stricken wetland in Sri Lanka, with elephant tracks through the mud.
Jason Edwards/National Geographic/Getty Images

The United States has lost more than half of its original wetlands due to drainage, conversion to farmland or other forms of development. The highest rates of wetland loss occurred between the 1950s and the 1970s, until conservation movements considerably slowed the rate of decline [source: EPA]. But wetlands are still under threat.

Human activity is probably the most prevalent cause of wetland destruction or degradation. Development -- whether it's drainage, damming to form lakes or ponds, adding pavement, or diverting water flow -- affects the soil's hydrologic condition, or the presence of water in the soil [source: Merriam-Webster]. If there's no water, there's no wetland.


Humans can't take all the blame, though. There also are natural threats to wetlands, such as droughts. Even though wetlands are sponge-like and can hold water in reserve for a long time, they can't do it forever. Some wetlands will eventually dry out if they aren't replenished. Wildlife can also be a detriment. Overgrazing by animals can cut down on the area's vegetation, leaving wetlands susceptible to erosion. Natural disasters like hurricanes or flooding can greatly erode a wetland area. While wetlands act as a buffer against these weather occurrences, they also pay the price with diminished vegetation and pollution from runoff.

Pollution als­o degrades wetlands and water quality. Again, wetlands act as a natural filter for polluted water, but they can only absorb so much. Pollution enters the water table through pesticides, sediment, sewage, fertilizers and many other forms. Once a wetland is polluted, it's difficult to clean it up. The best way to keep wetlands clean is to protect them from pollution in the first place, by ensuring a contaminant-free water supply.

Global warming is also a threat to wetlands. A study by the Pew Center on Global Climate Change found that as air temperatures rise, so do water temperatures. Because warmer waters are more productive, wetlands may end up overrun by algae, which degrades water quality and poses health problems­ to humans and animals. The algae bloom known as red tide releases toxins, which have killed thousands of fish. Eating affected shellfish can expose humans to these toxins. Breathing the air near a red tide can also cause respiratory issues in some people [source: CDC]. Also, many fish rely on cooler water to survive and can die out when smaller lakes or ponds warm up. Elevated temperatures also lead to reduced precipitation, which reduces the amount of runoff provided to wetlands [source: Pew Center].

So what can be done to save the wetlands? Keep reading to learn what the U.S. Clean Water Act and other private organizations are doing to protect wetlands.

The U.S. Clean Water Act

A sign identifies the wetlands route as a Coastal Heritage Greenway in Delaware.
A sign identifies the wetlands route as a Coastal Heritage Greenway in Delaware.
Steve St. John/National Geographic/Getty Images

The wetland preservation movement began in the U.S. in earnest with the Clean Water Act (CWA) of 1972. Although not specifically written to protect wetlands, the CWA is comprised of a series of regulations designed to prevent pollutants from contaminating U.S. waters. And, as we've already learned, pollution is a major threat to the health of wetlands.

The creation of the CWA was notable because for the first time, the U.S. federal government stepped up to regulate water quality. Up until then, each state was responsible for developing its own clean water standards. The CWA put the U.S. Environmental Protection Agency (EPA) in charge of implementing the goal of clean water nationwide.


Section 404 of the CWA specifically addresses wetland protection, prohibiting the release of any dredged or fill material into United States waters -- including wetlands. Any proposed development activities near or on wetlands must go through a regulation and permit process. The United States Army Corps of Engineers and the EPA jointly administer this process. The United States Fish and Wildlife Service (USFWS) also plays an advisory role. If this all sounds confusing, that's because it is. Let's break down the roles and responsibilities for the permit process.

The Army Corps of Engineers is responsible for day-to-day administration of the program, development and enforcement of policy, and verifying jurisdictional determinations of wetlands. The EPA also develops and interprets policy, oversees state and tribal rights, reviews permit applications and has the authority to deny the use of any wetland-defined area. Finally, the USFWS evaluates possible impacts on surrounding fish and wildlife for all proposed federal projects [source: EPA].

Because it can be difficult to delineate where some wetlands begin and end, some people feel the CWA does not truly protect all wetlands. One group may call an area wetlands, while another may designate it otherwise. The Emergency Wetlands Resources Act of 1986 attempted to address this problem by requiring the USFWS to address a national wetlands conservation plan, and required all states to include wetlands in their outdoor recreation plans.

However, the wetlands delineation issue is contentious and controversial, and continues to be to this day. For example, in 2006 a Supreme Court case known as Rapanos vs. United States clearly illustrated the division over the definition of wetlands. John Rapanos, a Michigan landowner, violated the Clean Water Act when he filled in and dried out wetlands on his property. However, Rapanos argued that because his property was 20 miles (32 kilometers) from a large body of water, it wasn't under a federal jurisdiction of wetlands protection.

The U.S. Supreme Court eventually returned a fractured decision. Four judges argued for a sharper restriction of the definition of federally preserved wetlands, believing that the existing definitions of wetlands were too vague and open to debate. Four judges argued in favor of retaining the broad wetland definitions created by the Army Corps of Engineers. Justice Anthony Kennedy, whose opinion controlled the outcome, stated that a wetland should have a "significant nexus" to a body of water in order to qualify for protection under the Clean Water Act. This opinion alarmed environmentalists, as it opened the door to remove protection from many wetlands. But Kennedy also stated that the Rapanos' property did meet the expert definition of wetlands, and its destruction was indeed a violation of the Clean Water Act [source: Greenhouse].

Besides U.S. federal regulations, what other actions have been taken to protect wetlands? Read on to find out how.

Preservation of Wetlands

U.S. Army Corp of Engineers wetlands restoration project in Empire, La.
U.S. Army Corp of Engineers wetlands restoration project in Empire, La.
Tyrone Turner/National Geographic/Getty Images

Many programs are in place not only to preserve wetlands, but to rehabilitate destroyed wetlands. In addition to U.S. federal regulations, individual states are encouraged to implement their own water-quality standards and wetlands protection programs.

The U.S. Environmental Protection Agency (EPA) estimates that 75 percent of wetlands are privately owned. So, the EPA and United States Fish and Wildlife Service (USFWS) offer financial assistance and expertise to landowners who would like to restore or protect wetlands on their own property. In addition, the EPA's "5 Star Restoration Program" provides grants to community organizations, students, landowners and local government groups for wetland and stream restoration projects. Since 1999, it has kicked off over 250 projects [source: EPA].


The rehabilitation of destroyed wetlands also is essential. It can take a long time for a wetland to form again naturally, but we can boost it in that direction. The EPA defines three types of rehabilitation: restoration, creation and enhancement.

Restoration returns a degraded or former wetland to its original state. A simple example of this is filling a previously drained ditch with water and letting nature take its course. Restoration can happen on small or very large scales. Wetland creation, or creating a wetland where one didn't exist before, is done by flooding an area or diverting a water source (like a stream, for example) to a dry area. Wetland creation can be difficult, as there are many factors at play, including recreating a viable and natural ecosystem. Taking an existing wetland and increasing its function is called wetland enhancement. If a wetland doesn't have a suitable amount of fish, for example, we can add water. Or if it doesn't have enough birds, we can decrease water. However, wetland enhancement usually comes with a tradeoff -- adding that water will indeed result in more fish, but it will also decrease the wetland's ability to hold back floodwater [source: EPA].

For more information on wetlands and other natural phenomena, take a look at the links on the next page.

Lots More Information

Related HowStuffWorks Articles

More Great Links



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