Wetlands and Estuaries

What is a coastal wetland? 

Coastal wetlands are transitional areas between dry land and open water that are either permanently or seasonally inundated with fresh, brackish, or salt water. They contain a range of plant and animal species that are uniquely adapted to the wet soil conditions, the type of water present, and the degree of inundation. 

Types of coastal wetlands include salt marshes, freshwater marshes, seagrass meadows, mangrove swamps, and forested swamps. 

What is an estuary? 

Estuaries are created where watersheds meet the ocean, bringing land-based waters and salt water from the ocean together. A dynamic ecosystem is created where river flows meet ocean tides. These regions offer food sources and shelter for many different species, including humans. 

Estuaries also face a variety of issues that alter their productivity as an ecosystem—many related to the watershed that supplies water from the mainland, including:  

• Water diversion (dams)
• Invasive species
• Nutrient pollution
• Severe weather events
• Habitat loss and degradation
• Declines in fish and wildlife populations
• Contaminants and pathogens
• Stormwater
• Drought 

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Why are coastal wetlands and estuaries important? 

Some of America’s largest cities and communities are located along wetlands and estuaries, such as New York-New Jersey Harbor, Chesapeake Bay, San Francisco Bay, Biscayne Bay, Puget Sound, Tampa Bay, and many others. Coastal wetlands and estuaries provide numerous critical benefits and services to society—these are known as ecosystem services. Specifically, they:  

• Protect coastal communities from storms and flooding
• Help prevent erosion
• Provide essential food, refuge, and nursery habitat for commercially and recreationally important species
• Improve water quality by filtering runoff and absorbing excess nutrients
• Decrease the effects of climate change by storing large quantities of the greenhouse gas carbon dioxide from the atmosphere
• Provide recreational opportunities like boating, hiking, hunting, fishing, kayaking, and wildlife/bird watching
• Serve as important areas of commerce, shipping activity, and ocean/port access

USGS Research 

Estuaries are the mixing point between land and coasts. The water that flows into them is critical to their high biological productivity. Changes to the quality, quantity, and type of water, sediment, and river flow affect everything from the types of plants and animals that live there, the landscapes that develop, and the ecosystem services provided to coastal communities.  

USGS scientists work in and bring expertise in hydrology, water chemistry, ecology, and sediment transport science, to integrate various information that can help forecast, predict, and identify threats or effects of changes. This helps decision-makers and resources managers develop science-based policies that balance sustainable use of these rich coastal ecosystems while maintaining their productivity for the benefit of all.  

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Storms, sea-level rise, and other elements of climate and coastal change often involve coastal engineering in order to accommodate human needs. These natural systems are highly adaptable. Many plant and animal species can move and grow in response to changing conditions, but some management actions like building coastal defense structures (e.g., seawalls and dikes) and maintaining roads restrict the ability of these coastal ecosystems to adapt or migrate.  When estuaries and coastal wetlands are constrained by seawalls or unable to move, they can be inundated, dried out or exposed to too much salt or fresh water. When they are depleted or destroyed, the benefits and services they provide to people and the environment could be diminished or lost. The loss of estuary and wetland health can have far-reaching effects such as reduced fish catch, diminished water quality, algal blooms, and lost habitat and food sources for many migratory species. 

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The USGS conducts a variety of research on coastal wetlands and estuaries that support management decisions of federal, state, regional, and local partners and help in evaluating the effectiveness of restoring these valuable habitats so that will continue to provide the most benefits to society and ecosystems.  

The USGS creates topobathymetric digital elevation models (DEMs) to assist with identifying flood, hurricane, and sea-level rise inundation hazard zones. These maps also assist with other earth science applications such as the development of sediment transport and storm surge models. The DEM data are important for a range of applications needed for climate change analysis in sensitive coastal regions. Access the Coastal National Elevation Database (CoNED) viewer. 

Past, Present, and Future Conditions

USGS scientists collect basic observational data on physical processes (e.g., storms and sea-level rise) and human activities (e.g., nutrient loading), develop numerical models of these data, and apply models to understand the past, present, and future states of these ecosystems. Through this work, USGS scientists can assess vulnerability (e.g., UnVegetated-Vegetated marsh Ratio or UVVR), water-quality conditions, and resilience and identify human activities that are preventing wetland migration and causing tidal restriction, impoundments, and other issues causing degradation. 

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Blue Carbon

Additionally, USGS scientists are working to better understand blue carbon—carbon that is stored in coastal and marine ecosystems. Terrestrial and aquatic ecosystems can capture and store carbon dioxide from the atmosphere, a process known as carbon sequestration. Though coastal ecosystems, such as wetlands, may be smaller in size when compared to say, a forest, they can sequester more carbon per unit area, making them an incredible climate change mitigation tool.  

USGS scientists are researching how environmental changes and human activities (e.g., land use management) can impact the ability of coastal wetlands and estuaries to sequester carbon and store it in soil and plant materials. These ecosystems are powerful carbon sinks and store carbon that has accumulated over hundreds to thousands of years. However, when coastal ecosystems are degraded or destroyed, their capacity to store carbon is diminished, and the carbon stored there can be released back into the atmosphere. Improved management of coastal wetlands and estuaries, leading to enhanced conservation and restoration, is therefore a crucial climate change mitigation strategy. Ultimately, USGS blue carbon research and science-based tools will help guide decision-making regarding climate change mitigation and adaptation, wetland restoration, coastal resilience, and carbon sequestration and storage.