World Wetlands Day is February 2, and there is no better time to tackle the question of what a wetland is, and why they are important. But before defining a wetland, let’s take a quick look at their characteristic feature: water

Humans rely on water to sustain our needs and daily activities, including drinking, hygiene, agriculture, transportation, electricity generation, and recreation. The water we used is called freshwater. Only about 3 percent of the water on Earth is considered freshwater.  

Freshwater is stored in freshwater ecosystems like rivers, streams, lakes, aquifers, and wetlands. Despite their critical importance to humans, freshwater ecosystems are globally threatened. Habitat loss, pollution, and excessive use are major contributors to their decline. 

Out of all the freshwater habitats, wetlands have suffered some of the greatest losses. The United States and much of the world has a long history of filling in wetlands, historically to make way for agriculture, but now wetlands are increasingly threatened by urbanization. As much as 87 percent of the world’s wetlands have been lost. In Indiana, the loss is nearly identical, with almost 85 percent of our original wetlands now gone from the state. So just what is a wetland? 

Wetlands are areas of land that are saturated with water, either seasonally (ephemeral wetland) or permanently, and are typically identified by the presence of the following:

  • Plants that love water, also known as hydrophytes 
  • Statured or wet soil, also known as hydric soil

Wetlands are transition zones between land and water. They have characteristics of both ecosystems, which means they are neither totally dry land or totally underwater. This is what makes wetlands so unique and able to support such high levels of biodiversity. 

An American bullfrog contemplating his life in the transition zone (wetland) Credit: Susie McGovern

Wetlands exist in all different climates and continents besides Antarctica. They are found along coastal areas, and inland areas near rivers or streams; near a spring or other groundwater source; or in a depression.

Government agencies in the United States classify wetlands based on different circumstances and characteristics. For example, the US Army Corps of Engineers defines a wetland based on plants, soils, and hydrology as laid out in the Corps of Engineers Wetlands Delineation Manual. This is used for regulatory purposes, including the implementation of Clean Water Act.

The US Fish and Wildlife Service classifies wetlands according to the Cowardin system, which includes five major types of wetlands and deep water habitats: marine (ocean), estuarine (estuary), lacustrine (lake), palustrine (marsh) and riverine (river). This classification system is the backbone of the National Wetlands Inventory (NWI) database

Common wetland types 

Swamp

A swamp is any wetland that is dominated by woody (hard-stemmed) plants, such as trees and shrubs. Swamps typically have saturated soils during the growing season and standing water during portions of the year. Swamps have nutrient rich soils and are highly productive at nutrient removal and flood mitigation.

Twin Swamps Nature Preserve located in Mt. Vernon, Indiana
Photo credit: Visit Indiana

Marsh

A marsh is a wetland that is frequently or continually saturated with water and dominated by emergent (soft-stemmed) plants, like cattails. Most marshes are fed by surface or groundwater. Marshes found along the coast can be saltwater or freshwater. Prairie potholes and the Florida Everglades are examples of marshes. 

Indiana used to be home to the largest inland marsh in the United States, the Grand Kankakee Marsh. Now, only portions of the Grand Kankakee are preserved. 

Celery Bog (which is actually a marsh) in West Lafayette, Indiana
Photo credit: Susie McGovern

Bog

A bog is an acidic wetland typically characterized by the presence of peat and sphagnum moss. Bogs are nutrient poor wetlands that contain anaerobic bacteria. Because of this, bogs are home to many carnivorous plants, which get their nutrients from bugs. These conditions also prevention decomposition of organic material, and many bogs are known to preserve things like pollen and even human bodies. Bogs receive most of their water from precipitation.

Pinhook Bog is a bog located in northwest Indiana. It is home to one third of Indiana’s rare or endangered plants. 

Elkhart Bog located in Elkhart, Indiana
Photo credit: Indiana DNR

Why are wetlands important?

  • Wetlands are a form of green infrastructure. Often considered nature’s wastewater treatment plants, wetlands are areas where water is purified and filtered. Wetlands intercept water as it moves through the water cycle, slowing down the flow and removing harmful pollutants. Wetland soils and plants play a critical role in water filtration and purification. Their storage and filtration abilities make them an incredibly important form of green infrastructure on the landscape.
  • Wetlands recharge and purify groundwater. As wetlands store and purify water above the surface, they also recharge groundwater below the surface by allowing water to slowly percolate back into our aquifers. Wetlands and groundwater are part of the same water cycle where water is continually exchanged above and below ground
  • Wetlands tackle water quality issues. Wetlands filter out harmful chemicals, nutrients (especially nitrogen and phosphorus), and sediment from urban stormwater and agricultural practices, which improves our water quality, making our waterways fishable and swimmable. They also tackle larger issues like algal blooms, dead zones, and fish kills, which are associated with excess nutrient pollution. One study estimates that the Congaree Bottomland Hardwood Swamp in South Carolina removes the same amount of pollutants as a multi-million dollar wastewater treatment facility. 
  • Wetlands support outdoor recreation and attract new residents. Outdoor recreation is a powerful economic driver across Indiana and the United States. According the Indiana Department of Natural Resources, 77 percent of US adults consider high-quality parks and recreation opportunities important factors when choosing a new place to live. Preserved, high quality wetlands can make for robust park and recreation areas. 
  • Wetlands protect biodiversity and provide critical wildlife habitat. 40 percent of all plant and animal species live or breed in wetlands, and approximately half of all federally listed endangered species depend on wetlands for survival. Ephemeral wetlands are particularly important to breeding amphibians since they don’t have enough water year-round to support predatory fish populations. 
  • Wetlands provide food and medicine and can be useful in regenerative agriculture efforts. For example, rice, a globally important agricultural commodity, is often grown in flooded fields that resemble or mimic wetlands. Wild rice (manoomin), which is a native plant cultivated in wetlands in the Great Lakes region, was and still is an important food staple to Indigenous Americans. Medicinal plants that grow in wetlands include elderberry, peppermint, silky dogwood, cranberry, alder, and jewelweed.
  • Wetlands provide agrotourism opportunities. In parts of the northeast United States, cranberries are cultivated in cranberry bogs. Some of these operations provide agrotourism opportunities like farm tours for locals and tourists, which stimulates the local economy. 
  • Spending time near wetlands can improve our health. Protected wetlands offer recreational opportunities, encouraging people to live healthier lifestyles through exercise and interaction with nature. Studies have shown that spending time near “blue spaces,” or areas with water, can increase happiness and improve mental health.

Are stormwater ponds wetlands?

Stormwater ponds are a common feature in urban environments. Many people wonder whether these stormwater ponds are considered wetlands. While stormwater ponds do contain water, they are not considered wetlands unless they are carefully designed to mimic wetlands. In this case, they are considered a constructed wetland. Let’s take a look at some of the differences between stormwater ponds and wetlands. 

Stormwater ponds are artificially created ecosystems that are primarily designed to receive stormwater from urban environments to prevent flooding. They typically receive water through a series of pipes, culverts, and outlets. Much of the pollutant removal of stormwater ponds is sediment settling and pollutant uptake through biological interactions in the pond. 

Because stormwater ponds often lack any native or wetland vegetation and are typically lined with rocky substrate or short grasses, their ability to remove pollutants is substantially reduced. The lack of plants also means there isn’t much food or habitat for wildlife, though occasionally some species will frequent the ponds. Stormwater ponds also have compacted soil bases which reduces water infiltration and aquifer recharge. In some cases, they are completely lined to protect the area from potentially harmful pollutants, which prevents the water from contacting the soil. 

These ponds also contain larger amounts of water that are more like deep water habitats, such as a lake. The water depth in ponds does not allow for the growth of many wetland plant species. Wetlands typically have more gentle slopes than stormwater ponds, which means they fill up at a slower rate than a pond would but cover more area across the landscape. 

Researchers at Cornell University have attempted to define what a pond is, due to a lack of comprehensive understanding of these ecosystems. They concluded that a pond is a small and shallow waterbody whose surface area is less than twelve acres, with less than 30 percent emergent vegetation. They also stated that ponds are functionally different than a wetland or lake.