What Is A Salt Marsh And How Is It Formed?

Salt marshes provide food sources for many species of wildlife.
Salt marshes provide food sources for many species of wildlife.

A number of salt marsh varieties exist throughout the world. Different types of salt marshes include open coast, drowned valley, back barrier, deltaic, embayment, and estuarine. Additionally, areas known as lagoons may also have salt marsh habitats around its borders. The distinction is often made based on the plants and animals that thrive in the area. According to some research, salt marshes cover at least 5,495,089 hectares across several countries. Some of the largest of these are found along the North Atlantic coastal regions.

What Is a Salt Marsh?

A salt marsh is a special type of wetland habitat that can be found along coastal regions throughout the world, although it is most commonly found in mid-range and high-range latitude areas. The comparable habitat in tropical areas is known as a mangrove. A salt marsh may also be known as a tidal marsh or a coastal salt marsh. The base of a salt marsh is made up of large amounts of peat, which consists of decomposing plant matter that may extend several feet in depth. The entire area is flooded by seawater at high tide and drained at low tide. This combination of flooding and peat soil creates an environment of low oxygen, referred to as hypoxia, that promotes the growth of special bacteria. Due to these conditions, only a few specific type of plants can survive here. A salt marsh is characterized by the growth of grass and low shrub species. The vast majority of these plants are salt tolerant in order to resist the saltwater conditions prevalent in this habitat. These plants help the salt marsh habitat to retain its sediment, which is generally deposited by rivers flowing into the ocean, by preventing erosion. In addition, salt marshes work to prevent flooding by taking in excessive rainfall.

How Is a Salt Marsh Formed?

Salt marshes generally form in coastal areas that are relatively sheltered from harsh ocean waves and where rivers or creeks deposit a special type of fine sediment. These areas of fine sediment are referred to as mud flats. As the sediment continues to collect, these flats grow in size and elevation. Flooding of the area becomes less intense due to the increase in elevation, which allows plants to move into the area. These plants reduce the speed at which the river or the creek flows into the ocean, allowing more sediment to settle. As the amounts of river sediment and plant species increases, the amount of sediment retained from high tide also increases. Over time, other plant species colonize the area.

Ecological Importance of Salt Marshes

The salt marsh habitat is considered one of the most diverse and productive ecosystems in the world. At high tide, the ocean water brings nutrients into the salt marsh and takes plant materials out of the area at low tide. These plant materials provide nutrients to marine wildlife in the ocean. Microorganisms and tiny insects help break down the organic matter within salt marshes, which is then consumed by larger species living within the habitat. As the saltwater comes in with the high tide, it brings large predatory species with the extra nutrients. These larger species take the opportunity to feed on the smaller species that permanently inhabit the salt marsh. When the tide moves out, it takes the larger species back to the ocean, where they often play an important role in the human fishing industry.

Salt marshes are also characterized by microhabitats within the same tidal marsh. At higher elevations, the level of salt in the water is less concentrated than at lower elevations where the ocean tidewater is able to reach. This difference in saline levels results in diverse types of plants, which are organized by salt tolerance levels with the most salt tolerant plants found at lower elevations.

Threats to Salt Marshes

The delicate balance of life within salt marshes is currently facing a number of threats, the vast majority of which are caused by humans. Two of the biggest threats are urban development and agricultural practices.

Effects of Urban Development on Salt Marshes

Given that most of the global population is concentrated along coastlines throughout the world, urban development is a significant threat to the ecological health of salt marshes. These habitats are seen as profitable seaside real estate and, as a result, are often converted into buildable land. If not used to host homes and businesses, marshlands have often been viewed as natural wastelands and utilized as such. Additionally, pollution in the form of urban runoff (which may contain industrial chemicals as well as human sewage) makes its way into salt marshes, where it contaminates the flora. This contaminated flora is then consumed by animal species and can even make its way back into the human diet due to bioaccumulation. As the nutrient and nitrogen levels of these habitats changes in response to human activity, the plants within salt marshes are also beginning to change. Plants that are typically located in the areas of lower elevation are beginning to encroach on those found in the higher elevation, resulting in a loss of biodiversity. This loss goes on to affect the animal species that rely on these habitats for food and shelter.

Effects of Agricultural Practices on Salt Marshes

Agricultural practices are also seen as a threat to salt marshes. This damage is primarily caused by the practice of converting marshland into a drier land that can then be used to sustain agricultural crops and livestock. This practice has been going on over hundreds of years and reduces the salt content of the water and soil, increases the level of sedimentation in the area, and decreases the speed and volume of water flowing into and out of the habitat. These changes go on to affect the types of plants that can thrive in salt marsh habitats, resulting in biodiversity loss. As seen in urban development, agricultural practices near salt marshes also result in increased nitrogen levels. This change in natural environment also works to upset the balance of flora and fauna found in these unique ecological habitats.

Destruction of Salt Marshes

As human activities around the world contribute to global climate change, global sea levels are on the rise. In salt marsh areas that have not yet been affected by urban development and agriculture, the rising sea levels are changing the salinity of the habitat. Additionally, the plants found here cannot withstand the flooding and resulting erosion caused by the change in sea elevation. The result is a completely destroyed salt marsh.


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