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Brackish Water Plants

Instructor: Amanda Robb
In this lesson, we'll be exploring brackish water plants. We'll look at the challenges these plants face living in brackish water and how different examples of brackish water plants are adapted to survive there.

What Is Brackish Water?

When it comes to vacations, there are some people that are die-hard ocean lovers. The salt, big waves, and sway of the tide can be the ultimate form of relaxation. Other people, however, grew up swimming in lakes, with their muddy banks, calm waters, and vegetation all around. The ocean is a saltwater body whereas lakes and rivers are freshwater, meaning they have a low salt content. Although we usually think of these two environments as the black and white options of the aquatic world, there's actually an intermediary body of water called brackish water.

Brackish water is water that contains a concentration of salinity between freshwater and the ocean. Freshwater generally contains zero parts per thousand (ppt) of salt, whereas saltwater is considered anything with over 35 ppt of salt. So, brackish water lies in the middle with a concentration of between 0.5 ppt and 35 ppt.

Brackish Water Plants

Making a home in brackish water is difficult. The ecosystems are bound to the tides with the environment being flooded and drained twice daily, which results in low oxygen levels and changing levels of acidity for plants. Harsh winds and water currents batter plants as well. But, perhaps the high salt concentrations can be the most challenging.

When you water plants at home, you want to use pure tap water. This ensures that water flows into the plant cells, making them stand up straight. Watering plants with salt water will have just the opposite effect. Due to osmosis, water will actually flow out of the plant cells, making it more dehydrated than before you applied the salt water. Plants living in brackish water all have special adaptations for dealing with the salt. Let's look at some examples next.

Smooth Cordgrass

Along the shores of the East Coast of the United States lie many estuaries, areas where freshwater rivers and streams empty into saltwater oceans creating brackish water ecosystems. One of the most prominent features in these ecosystems are the tall grasses lining the shore. One of these grasses is smooth cordgrass.


Smooth cordgrass grows in estuaries on the Atlantic coast
cordgrass


Growing anywhere from six inches to seven feet tall, this versatile grass has several adaptations to help it grow in the challenging brackish water ecosystem. First, it has a complex root system that helps it take hold in the sandy soil that is attacked daily by tides. This helps it stay put in a shoreline that is eroded by the current and tides. Smooth cordgrass can absorb water through its roots like other plant species, but it also has the ability to extract freshwater from the salt water that floods its habitat if necessary.

Black Needlerush

At first glance, this plant may seem as though it lacks leaves and simply contains shoots extending out of the ground. But, upon closer examination, one can see the black needlerush is aptly named as it is covered in tiny gray leaves pointed like needles.

This plant makes a home in salt marshes where its growth depends on the salinity of the brackish water. It grows tall, up to seven feet high in low salinity, but higher salt concentrations restrict its growth to only one foot and can be found along the south Atlantic and Gulf coast of the United States.

Like the smooth cordgrass, the black neeedlerush has adaptations to help it survive in the salt marshes. The small needlelike leaves prevent water loss, helping the needlerush avoid desiccation in the salty environment of the marsh.

It also has adaptations to help it survive in hypoxic conditions. Like many other species that live in tidal zones, needlerush has a special tissue called aerenchyma that acts like a straw, transporting oxygen from the leaves to the roots so they can make energy. They also have strategies that allow them to be resistant to the changes in pH that occur in salt marshes.

Mangrove Tree

The most iconic of all brackish water plants might be the mangrove tree. Mangrove trees are a family of over 80 different species living in coastal intertidal zones. These amazing plants have developed their characteristic aerial root systems to cope with the changing tides where they live. Mangrove species live in tropical and sub-tropical regions, such as Florida, the Caribbean, South America, Africa, Southeast Asia, the South Pacific Islands, and Australia.

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