Researchers turn to native aquatic plants to clean coastal waters

April 18, 2023
A research team is exploring the use of native aquatic grasses and rice to develop an efficient, cost effective method for removing excess nutrients and metal salts along the Gulf Coast.

To find a fast, efficient way to clear harmful chemicals along the Gulf of Mexico coastline, researchers are turning to something already familiar with the task – several species of native aquatic grasses and rice, according to a press release from the University of Houston.

The research team is studying the abilities of these flora to uptake concentrations of chemicals and heavy metals. Eventually, the researchers also hope to find helpful uses of the system’s by-products.

University of Houston’s Venkatesh Balan, associate professor of biotechnology in the Cullen College of Engineering’s Division of Technology

“But first, we must identify which species are best at removing what we don’t want – the chemicals and metals in our coastal water,” said Venkatesh Balan, a University of Houston associate professor of biotechnology.

The Managing Urban Runoff project is funded over three years with a $1.5 million grant from the U.S. EPA.

“In the process called eutrophication, the chemical fertilizers and soil amendments feed the algae in watersheds,” said Balan. “The result is heavy concentrations of excess nutrients such as nitrogen and phosphorus and metal salts such as copper sulfate. That combination feeds cyanobacteria, which produces algal bloom that yields toxins harmful to humans, fish, marine mammals and birds.”

Removing these substances from stormwater is necessary for maintaining ecological balance and keeping communities healthy.

Other methods of cleaning the water have been proven, including aeration, sprayable clay suspensions, chemical and biological additives, and ultrasonic technology. But they come with high costs.

Around the world, aquatic plants have long been on the job of reducing nitrogen, phosphorus, heavy metals and fine suspended particles within stormwater runoff, vastly improving the quality of water in the process.

To maximize the natural benefits, selected species of floating aquatic plants typically are nurtured by implanting hydroponically grown native grasses or wetland plants on durable synthetic mats. The plant tissue above the synthetic mat stores excess nutrients. The roots beneath release oxygen and provide a surface to support microorganism growth.

Even in deep or fluctuating waters, this configuration can treat a wide range of water quality and help restore a healthy population of fish and other wildlife inhabitants. The first key step in the challenge is to select the best species for the task.

“Grasses such as miscanthus, khus and cattail have excellent nutrient removal potential due to their long rooting systems. Rice plants have similar structures and are cultivated as floating aquatic plants in South Asia to remove excess nutrients in ponds and lakes,” Balan said. “Once the plants are growing, we can stabilize the water’s pH levels by adding artificial aeration to the system, which facilitates the reduction of algae growth.”

To get its many benefits, the system requires upkeep, including the regular harvesting of the plants. The synthetic mats also need to remain properly secured so that heavy winds cannot topple and sink the plants. Balan and the research team are refining a system of grouping the plants and mats by wire, so the clusters can be moved to the middle of the watershed to maximize efficiency then pulled back to the shoreline for easy harvesting.

While the floating aquatic plants currently have no commercial value once harvested, the team is seeking ways to transform the harvested plants into biochar, which has potential to increase organic carbon in soil and other agricultural amendments.

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