Wetlands are intricate ecosystems defined by the flooding or saturation of soil, resulting in low-oxygen environments that nurture a unique variety of plants, animals, and microbes. These organisms have developed specialized adaptations to thrive in conditions characterized by slow-moving or stagnant water. In Wetland Studies and Solutions, wetlands are typically categorized based on their soil types and plant life, including bogs, marshes, swamps, and other similar habitats. Understanding these classifications is essential for appreciating the vital roles wetlands play in our environment and their importance to biodiversity.

What is a Wetland?

Wetlands are areas where water covers the soil, or is present either at or near the surface of the soil all year or for varying periods of time during the year, including during the growing season. Water saturation (hydrology) largely determines how the soil develops and the types of plant and animal communities living in and on the soil. Wetlands may support both aquatic and terrestrial species. The prolonged presence of water creates conditions that favor the growth of specially adapted plants (hydrophytes) and promote the development of characteristic wetland (hydric) soils.

How are wetlands formed?

Although some wetlands can form relatively quickly, many others took thousands of years to develop. Here are some of the processes that form or modify wetlands:

Flooding of coastal lowlands

Extreme flooding during storms and rising sea level transforms some coastal lowlands to coastal marshes. Barrier islands or reefs protect these marshes from crashing waves. Coastal wetlands also form in areas where rivers reach the ocean. While flowing, the rivers deposit some sediment in coastal areas. Then, plants can take root and hold the soil firm to protect the marsh from the forces of tides and waves.

River floodplains

River floodplains develop from erosion processes and sediment depositing on riverbanks during floods. When there is enough water saturation on riverbanks, “riparian” wetlands form. These riparian wetlands change as new river channels form and floods either scrape away or deposit new sediment.

Glaciers

Glaciers helped to create wetlands in the northern states 9,000-12,000 years ago. Large wetlands formed when glaciers dammed rivers, scoured valleys, and reworked floodplains. As Earth’s climate warmed and the ice age ended, glaciers began to recede. As the glaciers moved, they left behind large blocks of ice which formed pits in the land. Many of these depressions later filled with water if they had poor drainage or intersected the water table. These areas became wetlands.

Other forces of nature

Wind action in the sand hills of Nebraska formed depressions, many of which have become wetlands. Wetlands may also form in “sink holes” and other areas where percolating water has dissolved bedrock. Earthquakes can create wetlands by damming rivers or causing land to drop down near the water table or shoreline. Waterfalls often have lush wetland vegetation under and around them, sustained by the spray. Coastal processes such as currents and wave action can form, sustain, modify, or eliminate wetlands over time.

People

Some “incidental” wetlands are formed when highway and dam construction, irrigation projects, or other human activities alter drainage patterns or impound water. Government agencies, conservation groups and individuals intentionally create and restore wetlands. Research to improve restoration methods continues.

Beavers

Beavers once played a more significant role in forming smaller inland wetlands by damming rivers and streams. Though trapping has greatly reduced the number of beavers in the U.S., recent wildlife protection measures have resulted in recovery of beaver populations. Beaver dams may last in excess of 100 years, though many are shorter-lived.

Categories of Wetlands

Wetlands vary widely because of regional and local differences in soils, topography, climate, hydrology, water chemistry, vegetation and other factors, including human disturbance. Indeed, wetlands are found from the tundra to the tropics and on every continent except Antarctica. Two general categories of wetlands are recognized: coastal or tidal wetlands and inland or non-tidal wetlands.

Coastal/Tidal Wetlands

Coastal/tidal wetlands in the United States, as their name suggests, are found along the Atlantic, Pacific, Alaskan and Gulf coasts. They are closely linked to our nation’s estuaries where sea water mixes with fresh water to form an environment of varying salinities. The salt water and the fluctuating water levels (due to tidal action) combine to create a rather difficult environment for most plants. Consequently, many shallow coastal areas are unvegetated mud flats or sand flats. Some plants, however, have successfully adapted to this environment. Certain grasses and grasslike plants that adapt to the saline conditions form the tidal salt marshes that are found along the Atlantic, Gulf, and Pacific coasts. Mangrove swamps, with salt-loving shrubs or trees, are common in tropical climates, such as in southern Florida and Puerto Rico. Some tidal freshwater wetlands form beyond the upper edges of tidal salt marshes where the influence of salt water ends.

Inland/Non-tidal Wetlands

Inland/non-tidal wetlands are most common on floodplains along rivers and streams (riparian wetlands), in isolated depressions surrounded by dry land (for example, playas, basins and “potholes”), along the margins of lakes and ponds, and in other low-lying areas where the groundwater intercepts the soil surface or where precipitation sufficiently saturates the soil (vernal pools and bogs). Inland wetlands include marshes and wet meadows dominated by herbaceous plants, swamps dominated by shrubs, and wooded swamps dominated by trees. Certain types of inland wetlands are common to particular regions of the country. For more information, see Wetland Classifications and Types for a full list.

Many of these wetlands are seasonal (they are dry one or more seasons every year), and, particularly in the arid and semiarid West, may be wet only periodically. The quantity of water present and the timing of its presence in part determine the functions of a wetland and its role in the environment. Even wetlands that appear dry at times for significant parts of the year such as vernal pools often provide critical habitat for wildlife adapted to breeding exclusively in these areas.

Why are Wetlands Important?

Wetlands are important features in the landscape that provide numerous beneficial services for people and for fish and wildlife. Some of these services, or functions, include protecting and improving water quality, providing fish and wildlife habitats, storing floodwaters and maintaining surface water flow during dry periods. These valuable functions are the result of the unique natural characteristics of wetlands.

Case Study: Tres Rios

The arid urban area of Phoenix, Arizona, serves an example of how wetlands support the economy, health, and wildlife of an area. In the early 1990s, city leaders worked with the Army Corps of Engineers, the Environmental Protection Agency, and local environmental groups to create a wetland, the Tres Rios Demonstration Project. Tres Rios receives its water from a wastewater facility serving the busy urban area of Phoenix, as well as the seasonal streams of the Gila, Salt, and Agua Fria rivers.

More than two million gallons of wastewater flow into Tres Rios every day. Thousands of birds flock to Tres Rios: waterfowl, such as ducks and cormorants; terrestrial species, such as sparrows and cardinals; and migratory species, such as blackbirds. Even raptors such as osprey inhabit Tres Rios.

The habitat established at Tres Rios was so successful that wildlife managers were forced to relocate beavers, native to Arizona marshes, because multiplied too quickly for the wetland to sustain.

Tres Rios cleans the wastewater that flows into it. The ecosystem acts as a filter for toxic chemicals. Its position along the Salt River also makes Tres Rios a natural flood-control mechanism.

Conclusion

Wetland Studies and Solutions highlight the critical role that wetlands play in maintaining ecological balance and supporting biodiversity. These unique ecosystems not only provide essential services such as water filtration, flood control, and habitat for various species, but they also serve as vital resources for human communities. Understanding the formation processes of wetlands, from natural phenomena to human influences, is crucial for their conservation and restoration.

As urban areas expand and climate change poses new challenges, the importance of protecting and restoring wetlands cannot be overstated. By implementing effective wetland management strategies and fostering community involvement, we can ensure that these invaluable ecosystems continue to thrive, benefiting both wildlife and human populations for generations to come.

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