Native aquatic plants could help clean coastal waters

In a newly funded three-year project – called Managing Urban Runoff – a team of researchers led by the University of Houston (UH) will examine the ability of several species of aquatic grasses and rice that can thrive in murky coastal waters to provide a fast and efficient way of clearing harmful chemicals along the Gulf of Mexico coastline. According to the experts, these water-loving flora can uptake concentrations of chemicals and heavy metals which end up in places where they should not be.

The pollution of coastal waters is caused by heavy rainstorms washing chemical fertilizers and soil amendments away from farmlands, household gardens, and lawns, leading to runoff accumulation along the Gulf Coast. 

“In the process called eutrophication, the chemical fertilizers and soil amendments feed the algae in watersheds. 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,” said project leader Venkatesh Balan, an associate professor of Biotechnology at UH.

Thus, to maintain ecological balance and keep coastal communities healthy, removing these substances from stormwater is necessary. While other methods of cleaning the water have already been identified – including aeration, sprayable clay suspensions, ultrasonic technology, and chemical and biological additives – they are rarely used due to their high costs.

However, several species of aquatic plants are known to reduce nitrogen, phosphorous, heavy metals, and fine suspended particles within stormwater runoff, significantly improving the quality of water in the process. To maximize these natural benefits, selected species are usually nurtured by implanting hydroponically grown native grasses or wetland plants on durable synthetic mats. While the plant tissues located above these mats store excess nutrients, the roots beneath release oxygen and support the growth of beneficial microorganisms.

“Gasses 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. 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,” Balan explained.

However, to maximize these plants’ benefits, the system requires upkeep, including the regular harvesting of the plants and the securing of the synthetic mats so that heavy winds cannot topple and sink the plants. The scientists are currently working on a system of grouping the plants and mats by wire, so the clusters can be moved in the middle of the watershed to maximize their efficiency, and then pulled back to the shore for easy harvesting. 

Although these floating aquatic plants have no commercial value when harvested, the researchers are looking for ways to transform them into biochar, which could potentially increase organic carbon concentrations in soil and other agricultural amendments.

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By Andrei Ionescu, Earth.com Staff Writer

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